Fatty acid status and dietary intake of
children and their caregivers from
three distinct communities
R.C. Ford
22989919
Dissertation submitted in fulfillment of the requirements for
the degree Magister Scientiae in Nutrition at the
Potchefstroom Campus of the North-West University
Supervisor:
Prof C.M. Smuts
Co-supervisor:
Prof M. Faber
December 2013
ABSTRACT
Background: Dietary fat intake particularly of omega-3 and omega-6 fatty acids play an
important role in growth and development and influence the risk of nutrition related non communicable diseases. These dietary intakes are reflected in the red blood cell (RBC) fatty acid profile.
Aim: The aim of this study was to assess the fatty acid profile (%) of red blood cell
membrane phospholipids in relation to the dietary intake of South African children aged 2 to 5 years, and of their mothers/caregivers from three communities, each with distinct dietary patterns.
Method: In this cross-sectional observational study, approximately 105 children, aged: 2-5
years and their mother/caregivers were selected from three different geographical areas. These included; the urban community of De Aar (n=105), the urban coastal community Ocean View (n=93) and the rural community of Sekhukhune District (n=104). The red blood cell membrane total phospholipid fatty acid profile was determined by gas chromatography. A 24-hour dietary recall was done for each child and mother/caregiver as well as a socio-demographic questionnaire answered by each mother/caregiver. The mean and standard deviations of the RBC fatty acids were determined and compared through an analysis of variance (ANOVA) test followed by a Bonferroni post hoc test. Age and gender were controlled for in the children and age was controlled for in the mothers/caregivers. The median dietary intake (quartile range) was compared between communities by a Kruskal-Wallis test. The relationship between RBC membrane total phospholipid fatty acid profile and dietary fatty acid intake was done by stratifying the data for the three groups combined into tertiles according to RBC fatty acid profile and comparing the median (quartile range) of the dietary fatty acid intake in the different strata.
Results: In the children, the total dietary fat, SFA and PUFA and omega-3 intake of De Aar
(34.2%, 11.9%, 5.9% and 0.2% of energy, respectively) and Ocean View (33.0%, 11.2%, 7.4% and 0.2% of energy, respectively) was significantly different to Sekhukhune (19.9%, 6.5%, 3.0% and 0.1% of energy, respectively). Eicosaipentanoic (EPA) and docosahexaenoic (DHA) and α-linolenic acid (ALA) mean intake in children in all three sites was lower than recommended. In children from De Aar the RBC membrane total phospholipids contained significantly higher SFA and trans-fat percentages, while children in Sekhukhune District had significantly higher PUFA, omega-6 and omega-3 percentages. The linoleic acid (LA) profile in children from Ocean View was significantly higher than in those
from De Aar and Sekhukhune District. The mother/caregivers’ dietary fat intake of total fat, SFA, PUFA and trans-fat was significantly higher in De Aar (31.7%, 10.5%, 6.3% and 0.2% of energy respectively) and Ocean View (37.4%, 12.1%, 8.5% and 0.59% of energy respectively) in comparison to Sekhukhune District (15.7%, 3.0%, 3.2% and 0.02% energy respectively). PUFA intakes were significantly higher in Ocean View (8.5% of energy). EPA, DHA and ALA dietary intakes were lower than recommended. The mother/caregiver’s RBC membrane total phospholipid SFA percentage was significantly higher in mothers/caregivers from De Aar and Ocean View whereas those from Sekhukhune District had significantly higher PUFA and omega-3 percentage.
Conclusion: Differences particularly between the urban areas of De Aar and Ocean View
and the rural area of Sekhukhune District were observed in dietary fat intake which was reflected in the red blood cell membrane total phospholipid fatty acid profile for children and mother/caregivers. Dietary omega-3 fatty acid intake was low in both children and mother/caregivers from all three study sites and is of concern.
Key words: Diet, fatty acids, red blood cell, phospholipid
OPSOMMING
Agtergrond: Dieetinname van vet en in die besonder van omega-3 en omega-6 vetsure,
speel 'n belangrike rol in groei en ontwikkeling en die risiko van voeding-verwante nie-oordraagbare siektes. Hierdie dieetinname word in die rooibloedsel (RBS) vetsuurprofiel weerspieël.
Doel: Om die vetsuurstatus in RBS tot verhouding van dieetinname van Suid-Afrikaanse
kinders tussen die ouderdomme van 2-5 jaar en hul moeders/versorgers van drie gemeenskappe, elk met verskillende dieetpatrone, te bepaal.
Metode: In hierdie dwarsdeursnee-waarnemingsstudie is ongeveer 105 kinders tussen die
ouderdomme 2-5 jaar en hul moeder/versorgers uit drie verskillende geografiese gebiede gekies. Dit sluit in: die stedelike gemeenskap van De Aar (n=105), die stedelike kusgemeenskap Ocean View (n=93) en die landelike gemeenskap van die Sekhukhune-distrik (n=104). Rooibloedselmembraan totale fosfolipiedvetsuurprofiel is deur gaschromatografie bepaal. 'n 24-uur dieetherroep is gedoen vir elke kind en moeder/versorger, sowel as 'n sosio-demografiese vraelys vir elke moeder/versorger. Die gemiddelde en standaardafwykings van die RBS-vetsure is bepaal en vergelyk deur middel van 'n analise van variansie (ANOVA)-toets gevolg deur 'n Bonferroni post hoc-toets. Daar is vir ouderdom en geslag beheer in die kinders en vir ouderdom in die moeders/versorgers. Die gemiddelde dieetinname (variasiewydte) tussen gemeenskappe is vergelyk deur 'n Kruskal-Wallis-toets. Die verhouding tussen RBS-vetsuurprofiel en dieetvetsuurinname is gedoen deur die data vir die drie groepe te kombineer en in tertiele te stratifiseer volgens RBS-vetsuurprofiel, en dan die mediaan (variasiewydte) van die dieetvetsuurinname in die verskillende strata te vergelyk.
Resultate: In die kinders, het die totale dieetvet, versadigde vetsure (VVS) en
poli-onversadigde vetsure (POVS) en omega-3 inname van De Aar (34.2%, 11.9%, 5.9% en 0.2% van die energie, onderskeidelik) en Ocean View (33.0%, 11.2%, 7.4% en 0.2% van die energie, onderskeidelik) aansienlik verskil van Sekhukhune (19.9%, 6.5%, 3.0% en 0.1% van die energie, onderskeidelik). Gemiddelde inname van eikosapentanoësuur (EPS), dokosaheksaenoësuur (DHS) en α-linoleensuur (ALS) in die kinders was laer as die aanbeveling in al drie areas. In kinders van De Aar was die RBS-membraan totale fosfolipiedvetsure aansienlik hoër in VVS en transvet persentasies, terwyl kinders in Sekhukhunedistrik beduidend hoër POVS, omega-6 en omega-3 persentasies gehad het. Die linoleïensuur-(LO) status in kinders van Ocean View was aansienlik hoër as in die van
De Aar en Sekhukhune-distrik. Die moeders/versorgers se dieetinname van totale vet, VVS, POVS en transvet was aansienlik hoër in De Aar (31.7%, 10.5%, 6.3% en 0.2% van die energie onderskeidelik) en Ocean View (37.4%, 12.1%, 8.5% en 0.59% van die energie onderskeidelik) in vergelyking met Sekhukhune-distrik (15.7%, 3.0%, 3.2% en 0.02% energie onderskeidelik). POVS inname was aansienlik hoër in Ocean View (8.5% van energie). EPS, DHS en ALS-dieetinname was almal laer as die dieetaanbeveling . Die moeders/versorgers se RBS membraan totale fosfolipied VVS persentasie was aansienlik hoër in moeders/versorgers van De Aar en Ocean View, terwyl die van Sekhukhune-distrik beduidend hoër POVS en omega-3 persentasie gehad het.
Gevolgtrekking: Groot verskille, veral tussen die stedelike gebiede van De Aar en Ocean
View en die landelike gebied van Sekhukhune-distrik, is in die kinders en moeder/ versorgers se dieetinname van vet, wat weerspieël is in die rooibloedselvetsuurstatus, waargeneem. Dieet-omega-3 vetsuurinname is laag in beide kinders en moeders/versorgers van al drie gemeenskappe, wat kommerwekkend is.
Sleutelwoorde: Dieet, vetsure, rooibloedselle, fosfolipied
Acknowledgements
I would firstly like to thank Sight and Life for funding this project and making it
possible and secondly to the Medical Research Council for parenting the
study. Thank you to all the children and mothers/caregivers from De Aar,
Ocean View and Sekhukhune District who participated in the study.
My personal gratitude goes to many people who have contributed towards the completion of this thesis:
Prof Marius Smuts, thank you for your time, expertise and calm guidance.
Prof Mieke Faber, thank you for your expertise, encouraging ways and attention to detail. My family and friends who supported me in whatever ways they could, which was in more ways than they realise.
The ladies at JB Consultancy, for your encouragement and support through the process and in particular, Jane Badham who set me on my path of furthering my studies.
Finally to my faithful friend Jesus, thank you.
Table of Contents Page
Abstract i
Acknowledgements v
List of tables ix
List of figures xi
List of acronyms xii
1. CHAPTER ONE: INTRODUCTION AND AIM 1
1.1 Background and problem statement 1
1.2 Purpose and importance of the study 3
1.3 Study contribution 3
1.4 Overall aim 5
1.5 Specific objectives 5
1.6 Structure of dissertation 7
2. CHAPTER TWO: LITERATURE REVIEW 8
2.1 Introduction 8
2.2 Fatty acids; general structure and function 8
2.2.1 Fatty acids; influence and role in cell membranes 9 2.2.2 Fatty acids influence and role in eicosanoids 11 2.3 Fat and fatty acid requirements and recommendations
2.3.1 Fat and fatty acid requirements and recommendations for adults 14 2.3.2 Fat and fatty acid requirements and recommendations for children 16
2.4 The role of dietary fatty acids in health 17
2.4.1 The role of total dietary fat intake in health 17 2.4.2 Dietary saturated fatty acids and their role in health 18 2.4.3 Dietary monounsaturated fatty acid and its role in health 20
2.4.4 Dietary polyunsaturated fatty acids and their role in health 21 2.4.4.1 Dietary omega-6 fatty acids and their role in health 23 2.4.4.2 Dietary omega-3 fatty acids and their role in health and
development 25
2.4.5 Dietary trans fatty acids and its role in health 27
2.5 The conversion of ALA to EPA and DHA. 28
2.5.1 Effect of dietary LA and ALA levels on the conversion of ALA to
EPA and DHA. 29
2.5.2 Effect of a fish based diet on the conversion of ALA to EPA and DHA 30
2.5.3 Influence of gender on LCPUFA metabolism 31
2.6 The dietary fat intake and dietary patterns of South Africans 31
2.7 Conclusion 35
3. CHAPTER THREE: METHODS 36
3.1 Study design 36
3.2 Study population 36
3.3 Measurements 38
3.3.1 Biochemical analysis, blood sampling 38
3.3.2 Dietary intake 41
3.3.3 Socio-demographic questionnaire 42
3.4 Statistical analysis 42
3.5 Ethical aspects 43
4. CHAPTER FOUR: RESULTS 44
4.1 Subjects 44
4.2 Dietary intake 45
4.3 Red blood cell membrane total phospholipid fatty acid profiles 50 4.4 Dietary fat intake according to RBC membrane fatty acid tertiles 54
5. CHAPTER FIVE: DISCUSSION 60
5.1 Introduction 60
5.2 Dietary fat intake 60
5.3 Red blood cell membrane phospholipid fatty acid profile 65 5.4 The relationships between red blood cell fatty acids and dietary fat intake 67
5.5 Strengths and limitations of the study 68
6. CHAPTER SIX: CONCLUSIONS AND RECOMMENDATIONS 69
6.1 Main findings 69
6.2 Conclusions and recommendations 69
REFERENCES 71
ADDENDUM A 85
List of tables Page
Table 1.1: Team / co-workers. 6
Table 2.1: Red blood cell fatty acids composition reported in studies. 11
Table 2.2: The physiological actions of eicosanoids derived from
arachidonic acid. 13
Table 2.3: The physiological actions of eicosanoids and docosanoids derived from docosahexaenoic acid and eicosapentaenoic acid. 13
Table 2.4: Adequate intake values of linoleic acid and α- linolenic acid for
adults. 16
Table 2.5: Adequate intake values of linoleic acid and α- linolenic acid for
children. 17
Table 2.6: The physiological roles and potential clinical benefits of very
long chain omega-3 fatty acids. 25
Table 2.7: South African studies which reported dietary fat intake. 34
Table 3.1: Anthropometry for children and non-pregnant caregivers per study site (personal communication with M. Faber). 38
Table 4.1: Socio-demographic information for the participants from De Aar,
Ocean View and Sekhukhune District. 44
Table 4.2: Median reported energy, macronutrient, cholesterol and fatty acid daily intake in children from De Aar, Ocean View
and Sekhukhune District. 46
Table 4.3: Median reported daily energy, macronutrient, cholesterol and fatty acid intake in mothers/caregivers from De Aar,
Ocean View and Sekhukhune District. 48
Table 4.4: Fish consumption as reported in the 24-hr dietary recall
for children and mothers/caregivers. 48
Table 4.5: Types and brands and percentage of spreads, oils and fish frequently used or consumed by children and mothers/caregivers from De Aar, Ocean View and Sekhukhune District. 49
Table 4.6: Mean percentage and ratios of red blood cell membrane total phospholipid fatty acid profile of the children from
De Aar, Ocean View and Sekhukhune district. 51
Table 4.7: Mean percentage of red blood cell membrane total
phospholipid fatty acid profile of mothers/caregivers from De Aar, Ocean View and Sekhukhune district. 52
Table 4.8: The dietary fatty acid daily intake of children according to red blood cell membrane omega-6 fatty acid profile tertiles which are expressed as a percentage of total fatty acids. 54
Table 4.9: The dietary fatty acid intake of children divided into red blood cell membrane omega-3 fatty acid profile tertiles which are
expressed as a percentage of total fatty acids. 55
Table 4.10: The dietary fatty acid intake of children divided into red blood
cell membrane docosahexaenoic acid profile tertiles which are expressed as a percentage of total fatty acids. 56
Table 4.11: The dietary fatty acid intake of motherscaregivers divided into
red blood cell membrane omega-6 fatty acid profile tertiles which are expressed as a percentage of total fatty acids. 57
Table 4.12: The dietary fatty acid intake of mothers/caregivers divided into
red blood cell membrane omega-3 fatty acid profile tertiles which are expressed as a percentage of total fatty acids. 58
Table 4.13: The dietary fatty acid intake of mothers/caregivers divided
into red blood cell membrane docosahexaenoic acid fatty acid profile tertiles which are expressed as a percentage
of total fatty acids. 59
List of figures Page
Figure 1.1 Outline of the parent and nested sub-study. 4
Figure 2.1 Overview of the mechanism by which fatty acid
exposure affects health outcomes. 10
Figure 2.2 Schematic pathway of the elongation and desaturation
pathway in the conversion of α- linolenic acid & linoleic acid to docosahexaenoic acid, eicosapentaenoic acid and
arachadonic acid. 29
Figure 2.3 Macronutrient distribution of total energy intake of
South African adult females by area. 32
Figure 3.1 Map of South African provinces displaying geographical areas
included in the study. 37
Figure 4.1 Mean percentages (±SD) of red blood cell membrane total phospholipid fatty acid profiles of children from De Aar,
Ocean View and Sekhukhune district. 53
Figure 4.2 Mean percentages (±SD) of red blood cell membrane total
phospholipid fatty acid profiles of the mothers/caregivers from
De Aar, Ocean View and Sekhukhune district. 53
List of acronyms
AI Adequate intake
ALA α-Linolenic acid
AMDR Acceptable macronutrient distribution range ARA Arachidonic acid
BMI Body Mass Index
CHD Coronary heart disease CVD Cardiovascular disease COX Cyclooxygenase DHA Docosahexaenoic acid DRI Dietary Reference Intakes EAR Estimated average requirement EFA Essential fatty acid
EPA Eicosapentaenoic acid FAME Fatty acid methyl esters FBDG Food based dietary guidelines
GC Gas chromatography
HDL High density lipoproteins HETE Hydroxyeicosatetraenoic
LA Linoleic acid
LCPUFA Long chain polyunsaturated fatty acids LDL Low density lipoprotein
LOX Lipooxygenase
LT Leukotrienes
MRC Medical Research Council MUFA Monounsaturated fatty acids
NFCS National Food Consumption Survey
NIRU Nutritional Intervention Research Unit NCD Non-communicable disease
NWU North-West University
PG Prostaglandins
PUFA Polyunsaturated fatty acids RBC Red blood cell
RDA Recommended daily allowance SFA Saturated fatty acids
TC Total cholesterol
TLC Thin layer chromatography
TXA Thromboxanes
UWC University of Western Cape
Chapter 1
Introduction and aim
1.1. Background and problem statement
South Africa is a widely diverse country with many varied living conditions and resources. In addition, South Africa has diverse ethnic groups with different traditional eating patterns (Steyn et al., 2006). The fatty acid composition of human red blood cells and plasma is greatly influenced by these different dietary patterns and the quality (type) of lipids consumed. This ultimately affects the individual’s health, contributing towards disease prevention or promotion, and a child’s development (Hulbert et al., 2005; Feunekes et al., 1993). Red blood cell (RBC) fatty acid profiles in particular, has been shown to be influenced by fatty acid intake, and this measure is used as a good indicator of a longer term (4 to 6 weeks) fatty acid intake (Baur et al., 2000).
General dietary fat intake recommendations throughout the human life cycle are based on the requirements to meet essential fatty acid (EFA) needs, to support neurodevelopment and cardiovascular health, and to prevent degenerative diseases (Uauy, 2009). During pregnancy, maternal EFA intake is of great important as the foetus and placenta are completely dependent on this supply (Cetin & Alvino, 2009). Arachidonic acid (ARA) and docosahexaenoic acid (DHA) are particularly vital in retinal and brain development of the foetus and are continually required from birth into childhood (Helland et al., 2003; Innis, 2007).
Recently, the importance and supply of DHA and eicosapentaenoic acid (EPA) through the diet has increasingly gained more interest. Evidence relates health benefits to fish intake and research suggests that this is due to the consumption of pre-formed EPA and DHA (Ruxton
et al., 2007, Hu et al., 2002). These play vital roles in cell membrane functioning, brain and
nervous system development and functioning, and in the manufacture of eicosanoids (Davis & Kris-Etherton, 2003). DHA could be considered a conditionally essential fatty acid, especially during the early developmental years (Gibson et al., 2011). A meta-analysis found that an increased fish consumption of 20 g per day could reduce coronary heart disease (CHD) mortality in adults by 7% (He et al., 2004). Improved verbal learning ability and memory were observed in South African children who were supplemented with a fish flour spread for six months (Dalton et al., 2009).
There is, however, a concern for low income communities that do not consume fish regularly, such as those situated inland (Briend et al., 2011). Alpha linolenic acid (ALA),
found in rapeseed oil, soybean oil, green leafy vegetables and certain nuts, is a precursor of EPA and DHA; however, it is questionable if the conversion is sufficient (Arterburn et al., 2006; Davis & Kris-Etherton, 2003). Approximately 5% to 10% and 2% to 5% of ALA has been found to be converted in a healthy human to EPA and DHA respectively (Emken et al., 1994; Gerster, 1998). A diet high in LA (>10% energy) reduces the conversion of ALA to EPA and DHA as it requires the same rate-limiting enzyme, ∆6 desaturase, also necessary in the conversion of LA to ARA (Briend et al., 2011; Burdge & Calder, 2005). Diets high in ALA have also been shown to inhibit the conversion of ALA to DHA. Rats fed diets with varying amounts of ALA developed increased plasma and liver tissue DHA levels up to the point at which ALA contributed 1% of their energy intake. Beyond that, the DHA plasma and liver tissue levels declined (Tu et al., 2010). Several human studies have, however, observed no increases in plasma DHA levels after increased dietary ALA intakes (Hussein et
al., 2004) whereas other studies have observed such an increase (Harper et al., 2005). The
background diet and balance between LA and ALA consumption is thus an important factor in determining the long chain polyunsaturated fatty acid (LCPUFA) profile, particularly in non-fish eaters. Further research is required on the quantities of LA and ALA consumed, and their effect on conversion rates (Briend et al., 2011; Gibson et al., 2011).
The more industrialised lifestyle and current ‘Western diet’ that many South Africans already follow or are transitioning towards, has resulted in an increased consumption of saturated, omega-6 PUFA and trans fatty acids, and a decrease in omega-3 fatty acid consumption (Steyn et al., 2006; Voster et al., 2011). A disproportionate omega-6:omega-3 fatty acid ratio has been associated with changes in the vascular membrane lipid composition, an increased prevalence of atherosclerosis, inflammatory disorders, cancers, osteoporosis and autoimmune diseases (Simopoulos, 2006). In 2010, non-communicable diseases accounted for around 29% of deaths in South Africa; 14% of these were caused by cardiovascular disease and diabetes (WHO, 2011). The quantity and quality of dietary fat consumed has been shown to have an influential role in these diseases (FAO, 2010). In moving forward with public health recommendations for dietary fat consumption, care needs to be taken, with the quality and quantity of fats being of importance (Briend et al., 2011).
1.2. Purpose and importance of the study
Omega-3 FA intake in low-income communities is possibly low, with possible increased intakes of omega-6 FA; this is evidently important and can affect child development and health maintenance throughout adulthood (Gibson et al., 2011; Prentice & Paul, 2000). However, limited literature is available from developing countries on the fatty acid status, intake and composition, particularly regarding omega-3 and omega-6 fatty acids (Briend et
al., 2011). Results from this study contribute specifically to the knowledge of the fatty acid
status, particularly the red blood cell membrane phospholipid profile, and the intake of essential fatty acids required for good health in South African children and women. The study also contributes towards questions remaining on the effectiveness and influences of habitual diets on the conversion of ALA to EPA and DHA.
1.3. Study contribution
This particular study forms part of a sub-study nested within a parent study conducted by the Nutritional Intervention Research Unit (NIRU) of the Medical Research Council (MRC), (see Figure 1.1). The aim of the parent study was to determine the vitamin A intake and status of 2- to 5-year-old South African children and that of their caregivers, located in four geographical sites, and over a wide range of dietary patterns. Three of the four geographical areas were selected for the nested study as they were assumed to be the most dietary diverse areas.
Secondary aims of the MRC study were to determine (i) the iron, zinc, anthropometric status and fatty acid profile of the children and their caregivers; (ii) the vitamin A, iron and zinc content of maize meal and bread collected from a randomly selected sub-sample of 25% of households, and (iii) the breast milk and serum retinol of a convenience sample of 50 breastfeeding mothers per their geographical site.
Geographical areas: - Rural area in
KwaZulu-Natal
- Urban area in the Northern Cape - Urban area in the Western Cape
- Rural area in Limpopo
Study population: 200 Randomly selected children aged 2-5 years per geographical area as well as the mother or caregiver. Measurements: 1. Blood Samples - Haemoglobin - Serum retinol - Serum ferritin - Serum zinc
- Red blood cell fatty acid profiles
- C-reactive protein & α 1-acid glycoprotein (infection indicator)
2. Dietary data
- 24-hr Dietary recall - Shortened quantified food frequency questionnaire - Short questionnaire on consumption of foods rich in fatty acids
3. Anthropometry
- Children’s height, weight, mid-upper arm circumference, triceps and subscapular skinfolds.
- Mother/caregiver’s height, weight and waist circumference
4. Socio-demographics & child morbidity questionnaires 5. Breast milk samples for retinol.
6. Collection & testing of maize meal and bread.
Study population:
105 out of the 200 randomly selected children aged 2-5 years per geographical area as well as the mother or caregiver was tested Geographical area:
- Urban area in the Northern Cape - Urban area in the Western Cape
- Rural area in Limpopo Province
Methods:
1. Blood samples
- Fatty acid profile of the RBC membrane
phospholipids
2. Dietary data
- 24-hr dietary recall - Fatty acids questionnaire
3. Socio-demographic N es ted s tudy Pare nt s tu dy
Figure 1.1 Outline of the parent and nested sub-study.
1.4. Overall aim
The aim of this study was to assess the fatty acid profile (%) of red blood cell membrane phospholipids in relation to the dietary intake of South African children aged 2 to 5 years, and of their mothers/caregivers from three communities, each with known distinct dietary patterns.
1.5. Specific objectives
1. To determine and compare the red blood cell membrane phospholipid fatty acid profile (%) of children aged 2 to 5 years and of their mothers/caregivers from an urban area in the Northern Cape, an urban area in the Western Cape and a rural area in Limpopo Province.
2.
To determine and compare the dietary fat intake of children aged 2 to 5 years and of their mothers/caregivers from an urban area in the Northern Cape, an urban area in the Western Cape, and a rural area in Limpopo Province; and to assess fat intake in reference to the recommended adequate intakes for linoleic acid (LA: C18:2 n-6) and alpha-linolenic acid (ALA: C18:3 n-3), as well as recommended EPA and DHA intakes.3.
To assess the relationships between red blood cell fatty acid levels and the dietary fat intake in children aged 2 to 5 years and of their mothers/caregivers4.
To determine the basic socio-demographic status of the children and of their mothers/caregivers in order to describe the context in which the study was done.Table 1.1 Team / co-workers.
Name
Affiliation
Responsibility
Prof Mieke Faber Chief Specialist Scientist, MRC
- Overall management of the parent project
- Negotiations
- Development of protocol, questionnaire and consent forms
- Recruitment and training of fieldworkers - Collection of information
- Analysis, interpretation and reporting of the data of the parent project
Dr Lize van Stuijvenberg Senior Specialist Scientist, MRC
- Blood sampling equipment
- Biochemical analysis of the blood and interpretation thereof
- Negotiations (Northern Cape province) Dr Paul Van Jaarsveld Senior Specialist Scientist,
MRC
- Blood sampling equipment
- Biochemical analysis of the blood and interpretation thereof
Prof Marius Smuts Senior lecturer,- Centre of Excellence for Nutrition, NWU
- Study supervisor
- Preparation of blood samples for fatty acid analysis
- Fatty acid lipid analysis Mrs Serene Schoeman Senior Scientist & professional
nurse, MRC
- Training and overseeing blood collection procedures
Dr Ernie Kunneke Senior lecturer, Division Dietetics, UWC
- Development of dietary intake tools - Checking of coded dietary data for 24hr
recall
- Analysis and interpretation of dietary data and validity analysis for the parent study
Mrs Katja Rossouw Independent (services rendered)
- Dietary data coding Mr Walter Dreyer Senior lab technician, Centre
of Excellence for Nutrition, NWU
- Fatty acid analysis Ms Rosalyn Ford MSc. Nutrition student, Centre
of Excellence for Nutrition, NWU
- Preparation of blood samples for fatty acid analysis
- Fatty acid lipid analysis
- Data entry of short questionnaire on use of FA-rich foods
- Statistical analysis of fatty acid composition
Fieldworkers Locally recruited - Recruiting of participants - Administering 24hr recalls and
questionnaires
Mrs Lee-Ann Human Research Technician - MRC - Data capturing, cleaning and tabulation for parent study
NWU– North West University, MRC – Medical Research Council, UWC – University of Western Cape
1.6. Structure of dissertation
This dissertation is made up of six chapters that include the following: Chapter 1: General introduction and aim of the study
Chapter 2: Literature review
Chapter 3: Study design and methodology Chapter 4: Study results
Chapter 5: Discussion of results
Chapter 6: Conclusions and recommendations of the study
Chapter 2
Literature review
2.1. Introduction
In 2003, the World Health Organization (WHO) reported an increased global trend in fat intake; as countries became more developed and industrialised, these increases were observed, reflecting effects of nutrition transition (WHO, 2003). South Africa is also a country experiencing nutrition transition and urbanisation but at the same has the stark contrast of its rural areas (Steyn et al., 2006). Fat intake is greatly influenced by these dietary transitions and habits, and is reflected in the red blood cell fatty acid profile, influencing health outcomes (Calder, 2012). Dietary fat plays a key role in certain chronic diseases such as cardiovascular disease (CVD), from which approximately 17 million people die worldwide per annum. Eleven per cent of deaths in 2010 in South Africa were due to CVD (WHO, 2011). Alternatively, a low fat intake, especially in children, will influence growth and development (Uauy, 2009). This literature review will look at the functions of fatty acids in the body, the current recommendations and requirements of dietary fatty acids and how those recommendations influence health outcomes. Lastly, dietary patterns of South Africans and studies of South African fat intakes will be reviewed.
2.2. Fatty acids; general structure and function
Fatty acids are carboxylic acids comprising of a hydrophobic hydrocarbon chain with a terminal hydrophilic carboxyl group (-COOH). Hydrocarbon chains are commonly even-numbered, with the most prevalent length being 16 to18 carbons in an unbranched form (Berdanier & Zempleni, 2009: 258). Fatty acids are classified according to the number of carbons in the chain, the degree of saturation and the position of the first double bond. Unsaturation refers to the amount of double bonds present in the fatty acid chain. Saturated fatty acids (SFA) do not contain double bonds, while monounsaturated fatty acids (MUFA) contain one and polyunsaturated fatty acids (PUFA) have two or more. Double bonds are predominantly present in cis rather than in trans-configurations, causing the fatty acid to form a bend in the chain (Champe et al., 2008: 696). The carbon chain length and degree of unsaturation also influences the fatty acids’ rate of oxidation in the body. The rate of oxidation is decreased as the fatty acid chain length increases; unsaturated fatty acids are also more susceptible to oxidation than saturated fatty acids (DeLany et al., 2000). This finding could contribute to knowledge on the consumption of different types of dietary fat and its role in obesity (DeLany et al., 2000). The human body mainly stores fatty acids as
palmitic and stearic acids, due to their decreased oxidation rates (Mahan & Escott-Stump, 2004: 54).
Different organisms generally have the ability to synthesise and elongate fatty acids according to their needs, therefore, food from varied plants and animals will provide a variety of fatty acids through the diet (Mahan & Escott-Stump, 2004: 54). The human body also has the ability to synthesise most fatty acids from the metabolic breakdown of sugars, some amino acids and other fatty acids. De novo synthesis of fatty acids is influenced by background diet, exercise, genetics, hormones and other factors (FAO, 2010). Palmitic acid (C16:0), a saturated straight-chain fatty acid is initially synthesised. Through the contribution of carbon atoms from acetyl CoA, palmitic acid can be transformed into different fatty acids with the exception of long-chain fatty acids (LCFA), the omega-3 ALA and omega-6 LA (Devlin, 2002). Animal tissue (including human) is unable to introduce a double bond to a carbon position before the ninth carbon from the carboxyl or delta end (Uauy et al., 1999). These fatty acids, LA and ALA, are thus considered essential fatty acids (EFA) and need to be consumed through the diet (Uauy et al., 1999). Once in the body, fatty acids can be oxidised for energy, stored as energy in the resynthesized form of triacylglycerol, perform a structural role in membranes, or be converted into eicosanoids (Berdanier & Zempleni, 2009: 260).
2.2.1. Fatty acids: influence and role in cell membranes
The unique hydrophobic and hydrophilic (amphiphatic) nature of fatty acids plays a critical role in the biological functioning in the complex structure of cell membranes. An extremely organised lipid bilayer with embedded proteins is formed in each membrane, serving as a barrier between the cell and its environment (Champe et al., 2008: 697). Phosphoglycerides made up of two fatty acids attached to glycerol which is attached to phosphoric acid, both through ester bonds, is the main constituent of the membrane bilayer (Pollard & Earnshaw, 2008). It is aligned with the polar head facing the water and the fatty acid chains facing inwards (Pollard & Earnshaw, 2008). The fluidity and biochemical functioning is greatly influenced by the nature of the fatty acids. ‘Kinks’ found in fatty acids created by double bonds in the cis formation prevent the fatty acids in membranes from packing together tightly, thus increasing fluidity in the membrane (Pollard & Earnshaw, 2008). A membrane with a high PUFA content, particularly omega-3 LCPUFA, can significantly influence the physical properties and functioning of the membrane. Membrane order and raft structure are influenced, which in turn affects cell signaling pathways resulting in the changing of transcription factor activity, gene expression and enzyme activity. Rafts are sub-domains of cell membranes containing proteins involved in cell signaling (Calder, 2012; Harris, 2008).
Omega-6 and omega-3 fatty acids are also made available from the membrane through phospholipase A2 which serve as substrates for eicosanoid and resolvin production. All of
these factors ultimately affect health outcomes (Figure 2.1) (Calder, 2012; Harris, 2008) Fatty acid content
Membrane composition Receptors
Fluidity Raft Assembly
Signals
Cell responses Altered physiology Influences health
Figure 2.1 Overview of the mechanism by which fatty acid exposure affects health outcomes
(Adapted from Calder, 2012).
Fatty acid composition examined through plasma and red blood cell membranes serve as effective biochemical markers and indicators of dietary fat intake, validating food frequency questionnaires (FFQ) and 24-hour dietary recalls. Results from studies where red blood cell fatty acid composition was determined are shown in table 2.1.
As fatty acids are exchangeable between plasma and red blood cells (Reed et al., 1968), plasma is more indicative of a shorter term dietary intake, whereas red blood cell fatty acid composition is a longer term (4-6 weeks) dietary intake indicator (Baur et al., 2000; Katan et
al.,1997). The SFA and MUFA content in cell membranes remains relatively constant with
omega-3 and omega-6 fatty acid content changing more frequently due to changes in the diet. A possible explanation for this is that the body cannot produce EFA de novo (Clamp et
al., 1997; Sun et al., 2007). SFA and MUFA on the other hand, can be produced in the body
from carbohydrates and amino acids and have therefore been found to ineffectively reflect the dietary fat intake (Sun et al., 2007). The evidence of red blood cell fatty acid composition serving as a biomarker validating dietary fat intake also confirms that the fatty acid content in cell membranes can be altered through the diet.
Substrates for eicosanoids, resolvins, etc.
Table 2.1 Red blood cell fatty acid composition reported in studies. Study & RBC Orton et al., 2008 RBC membrane Riśe et al., 2007 RBC total fatty acids Sun et al., 2007 RBC total fatty acids. Knoll et al., 2011 RBC total fatty acids. Study population n=404, M & F aged: 1 – 11 years, American n=10, M & F aged: 24 – 57 years, Italian n=306, F aged: 43 – 69 years, American n=26, M & F aged: 18 – 54 years, Kenyan Maasai SFA (%) (Mean ± SD) - 49.36 ± 3.02 34.37 ± 1.60 44.07 ± 1.18 MUFA (%) (Mean ± SD) - 18.92 ± 1.32 18.64 ± 1.24 19.85 ± 1.37 PUFA (%) (Mean ± SD) - 31.7 ± 3.76 43.48 ± 1.77 36.08 ± 1.52 Omega-6 (%) (Mean ± SD) 24.93 ± 4.39 - 33.91 ± 1.79 29.29 ± 1.93 Omega-3 (%) (Mean ± SD) 3.81 ± 1.32 - 7.06 ±1.90 6.13 ± 0.86 ARA (%) (Mean ± SD) 11.12 ± 2.23 12.88 ± 2.09 14.63 ± 1.29 13.66 ± 1.40 EPA (%) (Mean ± SD) 2.34 0.42 ± 0.12 1.15 ± 0.91 0.84 ± 0.27 DHA (%) (Mean ± SD) 3.24 ± 1.19 3.71 ± 1.09 2.23 ± 0.64
RBC: red blood cells; M: males; F: females; SFA: saturated fatty acids; MUFA: monounsaturated fatty acids; PUFA: polyunsaturated fatty acids; ARA: arachadonic acid; EPA: eicosapentaenoic acid; DHA: docosahexaenoic acid; SD: Standard deviation.
2.2.2. Dietary fatty acids role and influence in eicosanoids
The LCPUFA, particularly ARA, EPA and DHA, play an essential role as precursors of eicosanoids and docosanoids which function in the body as autocrine and paracrine mediators (Uauy et al., 1999). They make up prostaglandins (PG), prostacyclins, thromboxanes, leukotrienes, resolvins and neuroprotectins. The 20 carbon fatty acids, through the addition of oxygen and cyclisation, are formed into eicosanoids and docosanoids
(Berdanier & Zempleni, 2009: 282). The physiological functioning of eicosanoids and docosanoids range from inflammation modulation, platelet aggregation, immune response, cell growth and proliferation, and contraction and dilation of smooth muscle cells (Table 2.2 & 2.3) (FAO, 2010). Cytokines and other stimuli signal for the formation of eicosanoids which are stimulated by mediators produced from LCPUFA (Calder, 2006). ARA and EPA compete for the same enzymes (desaturase and COX); therefore, the concentration of fatty acids in the cell membrane will determine which eicosanoids are formed. ARA is typically more abundant in the cell membrane which results in eicosanoids produced from ARA being more dominant. Often, but not always, these eicosanoids also have a more potent effect (Calder, 2009). However, this production can be altered through an increased dietary intake of EPA and DHA, which occurs in a dose-response manner (FAO, 2010). Intervention studies in humans involving the supplementation of omega-3 rich oils, resulted in a decreased production of prostaglandin E2, leukotriene B4 and interleukin 1 and 6 (Kelley et al., 1999;
Rees et al., 2006; Trebble et al., 2003). The cyclooxygenase reaction can also be halted with the use of anti-inflammatory medication such as aspirin, which blocks the functioning of cyclooxygenase (Berdanier & Zempleni, 2009: 283).
Table 2.2 The physiological actions of eicosanoids derived from arachidonic acid (Sourced
from FAO, 2010).
Eicosanoid Physiological action
PGE2 pro-inflammatory, pro-aggregatory, suppresses immune response, promotes cell growth, proliferation, vasodilation, bronchoconstriction;
mild anti-inflammatory (inhibits 5-LOX and so decreases inflammatory 4-series LT, induces 15-LOX which promotes formation of anti-inflammatory lipoxins)
PGI2 anti-inflammatory, inhibits platelet aggregation, potent vasodilator TXA2 potent platelet aggregation, potent vasoconstrictor
PGD2 inhibits platelet aggregation, vasodilation, promotes sleep PGF2a induces smooth muscle contraction, uterine contraction
LTB4 pro-inflammatory, causes neutrophil aggregation, neutrophil & eosinophil chemotaxis
LTC4 pro-inflammatory, promotes endothelial cell permeability, contracts smooth muscle cells, constricts
peripheral airways
LTD4 contracts smooth muscle cells, constricts peripheral airways 12-HETE neutrophil chemotaxis, stimulates glucose-induced insulin secretion 15-HETE inhibits 5- and 12-lipoxygenase
Lipoxin A superoxide anion generation, chemotaxis Lipoxin B inhibits NK cell activity
PGE2: prostaglandin E2, LOX: lipooxygenase; LT: leukotriene; PGI2: prostacyclins, TXA2: thromboxanes A2, PGD2:
prostaglandin D2, PGF2a: prostaglandin F2 LTB4: leukotriene B4, LTC4: leukotrienes C4, LTD4: leukotrienes,
12-HETE: 12-hydroxyeicosatetraenoic acid, 15-12-HETE: 15- hydroxyeicosatetraenoic, NK: natural killer.
Table 2.3 The physiological actions of eicosanoids and docosanoids derived from
docosahexaenoic acid and eicosapentaenoic acid (Sourced from FAO, 2010).
Eicosanoid/ Docosanoid
Physiological action
PGE3 mild anti-aggregatory, vasodilation PGI3 mild anti-aggregatory
TXA3 mild pro-aggregatory EPA Resolvin E1 potent anti-inflammatory DHA Resolvin D potent anti-inflammatory DHA Protectin D1 potent anti-inflammatory
PGE3: prostaglandin E3, PGI3: prostacyclins3, TXA3: thromboxanes A3, EPA: eicosapentaenoic acid; DHA:
docosahexaenoic acid.
Inflammation is a defense mechanism in the body. This reaction protects the body against infection and injury by promoting the killing of pathogens and repairing of tissues. It aims to restore homeostasis in the affected area and should be a regulated process that doesn’t cause additional damage (Calder, 2009). Imbalances of eicosanoid production and an increased concentration of eicosanoids formed from ARA can result in thrombosis, kidney disease, inflammation, asthma and inflammatory bowel disease, along with other inflammatory diseases (Calder, 2006). It should, however, be noted that new research has discovered that not all ARA-derived eicosanoids can simply be described as pro-inflammatory. PGE2 has been discovered to reduce the inflammatory leukotriene production
as well as promote the production of resolving lipoxin A4 (Calder, 2009). PG D3 are
eicosanoids produced from EPA, through their functionings the action of ARA-derived PG D2
is decreased(Calder, 2012). Traditionally, research around omega-3 fatty acid eicosanoids focused on EPA and its influence on eicosanoid production. The discovery of DHA derived eicosanoids called resolvins, and their powerful anti-inflammatory effects, has now opened a door to new research in the mechanisms and effectiveness of omega-3’s anti-inflammatory actions (Calder, 2009).
2.3. Fatty acid requirements and recommendations
2.3.1. Fat requirements and recommendations for adults
Aside from its functions in the body, fat also improves the taste and acceptability of food. It contributes towards the food’s texture, aroma and flavour and serves as a cooking medium, thus playing an integral part in many meals. It also affects the satiety level of a meal by slowing gastric emptying and intestinal motility (Uauy & Dangour, 2009). Recommendations for fats and fatty acids in humans are set in order to meet essential fatty acid requirements, to support neurodevelopment and cardiovascular health, and prevent degenerative diseases throughout the life cycle (Uauy, 2009). Following an International Meeting on fatty acids held in Barcelona, a South African fatty acids International Expert Meeting was subsequently held in Cape Town in 2009 (Health significance of fat quality in the diet). Recommendations on the quantity and quality of dietary fat intake were made for individuals of two years of age and older. These were adopted from the guidelines given at the International Meeting in Barcelona (Diekman et al., 2009). Total fat should contribute up to 30% of daily energy intake, with SFA providing no more than 10%, essential PUFA 6% to10%, and with omega-6 and omega-3 providing 5% to 8% and 1% to 2%, respectively. The intake of trans-fatty acids should contribute less than 1% of daily energy intake with MUFA making up the remaining fat energy intake (Diekman et al., 2009). For adults, a minimum of 15% of total energy intake
provided by fat is needed to ensure sufficient energy and essential fatty acid intake, and to facilitate fat-soluble vitamin absorption. Women of reproductive age and adults with a BMI of less than 18.5 kg/m² require a minimum fat energy intake of 20% (Jequier, 1999).
No dietary reference intakes (DRI) are set for total fat or SFA and MUFA intake, as there is insufficient information to set a precise amount of intake for inadequacy as well as for preventing chronic disease (National Research Council, 2005). As LA and ALA are essential fatty acids, adequate intake (AI) levels have been determined. Insufficient scientific evidence is available for setting an estimated average requirement (EAR) or a recommended dietary allowance (RDA), and thus AI levels have been determined by the median intake of fatty acids of a group of healthy Americans (National Research Council 2005). Table 2.4 shows the AI requirements determined for different adult age groups. Dietary fat intake recommendations have also been given in terms of acceptable macronutrient distribution range (AMDR). AMDR is the range given as a percentage intake of an energy source which provides for sufficient intake of essential nutrients as well as being associated with a decreased risk of chronic disease. AMDR for fat intake is 20% to 35% of energy; CHD was largely taken into account when determining this (National Research Council 2005). The recommended AMDR for DHA and EPA is between 0.25 g to 2.0 g per day (FAO, 2010). This can be achieved by consuming fish twice a week, preferably fatty fish. One portion (125 g) of fatty fish would provide approximately 2 g/100 g of EPA and DHA, whereas one portion (125 g) of lean fish would provide around 0.2 g/100 g of DHA and EPA (Kris-Etherton & Innis, 2007; Tur et al., 2012). Pregnant and lactating women are advised to consume 0.3 g of EPA and DHA per day; DHA should make up 0.2 g of this. The upper AMDR for DHA is set at 2.0 g/day, however, for those suffering from CHD, an increased intake of 3.0 g per day is advised (FAO, 2010).
Table 2.4 Adequate intake values of linoleic acid and α- linolenic acid for adults (Adapted
from National Research Council, 2005).
Age Category Linoleic Acid AI g/day
α- Linolenic Acid AI g/day
Males Females Males Females
19 – 30 years 17 12 1.6 1.1 31 – 50 years 17 12 1.6 1.1 51 – 70 years 14 11 1.6 1.1 Pregnancy - 13 - 1.4 Lactation - 13 - 1.3 AI – Adequate intake
Public health messages on fat consumption, according to an International Meeting held in Barcelona in 2009, tried to change consumer perceptions from the reduction of quantity of fat in the diet, to rather consuming a better quality of fat (Diekman et al., 2009). Foods containing fat of a lower quality include those with higher SFA content and industrially produced trans-fats. The higher quality fats considered as those high in PUFA and MUFA (Smuts & Wolmarans, 2013). The current South African food-based dietary guidelines (FBDG) recommend South Africans to ‘use fat sparingly and to choose vegetable oils rather than hard fats’ (Smuts & Wolmarans, 2013). SFA consumed through animal and plant sources should be replaced by PUFA and MUFA, and oily fish should also be consumed regularly in the diet (Smuts & Wolmarans, 2013).
2.3.2. Fat and fatty acid requirements and recommendations for children
Fat requirements for children are determined by similar criteria to those for adults – provision of energy and essential fatty acids, and an adequate amount to allow fat-soluble vitamin absorption (Prentice & Paul, 2000). In addition to the provision of energy, children should have a sufficient supply of dietary lipids for fat deposition which can be stored and used at times of low intakes such as food shortages or with infections or diarrhoea, particularly in low-income communities (Koletzko, 1999). Previously mentioned recommendations set by South African experts are given from the age of 2 years (Diekman et al., 2009), thus covering the requirements for children. Table 2.5 shows AI levels of LA and ALA determined for children (National Research Council, 2005). By the age of two years, children should be eating with the family and ideally should be receiving the recommended two servings of fish
a week (Uauy & Dangour, 2009). Fats serve as an important energy source in the human body. One gram of fat provides 37.7 kJ compared to the 16.8 kJ provided by one gram of protein and carbohydrates (Uauy & Dangour, 2009). In growing children, fats provide an important energy source. Uauy and Dangour (2009) even recommend a total dietary fat intake in children (>2 years of age) of between 30–40% of energy, depending on the child’s activity.
Table 2.5 Adequate intake values of linoleic acid and α- linolenic acid for children (Adapted
from National Research Council, 2005).
Age Category Linoleic Acid AI g/day
α- Linolenic Acid AI g/day
Males Females Males Females
1 – 3 years 7 7 0.7 0.7
4 – 8 years 10 10 0.9 0.9
9 – 13 years 12 10 1.2 1.0
14 – 18 years 16 11 1.6 1.1
AI – Adequate intake
2.4 The role of dietary fatty acids in health
Fats are required through the lifespan, for development and growth in the early years and later in life, when they play a significant role in nutrition-related non-communicable disease risks (Smuts & Wolmarans, 2013). As lipid research progresses, the focus is increasingly on individual fatty acids and their role in human health and development, in which it is suggested that the type of fat is of greater importance than the total fat intake (Smuts & Wolmarans, 2013; Uauy, 2009).
2.4.1 The role of total dietary fat intake in health
The risk of certain cancers, diabetes, coronary heart disease (CHD) and stroke is augmented in those who are overweight (BMI 25 – 30) and obese (BMI ≥30), making it a concern for public health authorities (FAO, 2010). In high-income and upper-middle income countries, more than half of the adults were reported to be overweight, with one fifth and one quarter respectively, being obese (WHO, 2011). An increase of 15% to 24% and 10% to 16% of overweight people was seen in lower-middle and low-income countries, and a 3% to 6% and 2% to 4% increase in obesity has been seen within the last three decades (WHO,
2011). South Africa is included in this concern as the prevalence of overweight is estimated to be 65.4%, of which 31.3% are obese (WHO, 2011). It is currently debatable whether or not a high total fat intake contributes to weight gain. Excess body fat accumulation is caused by the intake of excess energy greater than what is required for growth, maintenance and physical activity. The provision of energy could be from either fat or carbohydrates; while the fat and water content of food largely determine the energy density of the diet (Uauy, 2009). A meta-analysis done on 33 randomised controlled trials and 10 cohort studies, investigated the relationship between total fat intake and body weight in both adults and children (Hooper
et al., 2012). All the randomised control trial results were consistent in that the majority who
were placed on a lower fat diet had a small but significant and sustained weight loss. In accordance with the evidence, weight loss should also be seen in children decreasing their total fat intake (Hooper et al., 2012). On the other hand, studies involving low fat diets had no influence in decreasing obesity (Marantz et al., 2008). Little or no association between fat intake and weight gain and obesity has been found in other observational studies (Field et
al., 2007; Howard et al., 2006).
8
2.4.2 Dietary saturated fatty acids and their role in health
Epidemiological interventions and animal studies have led public health authorities to advise the lowering of dietary SFAs in an attempt to decrease the prevalence of CHD (Siri-Tarino et
al., 2010; Baum et al., 2012). Dietary SFAs, consumed by humans mainly through animal
and dairy products, have been shown to increase total blood cholesterol levels and low density lipoprotein (LDL) in a dose-related manner (Hegsted et al., 1965; Mensink & Katan, 1992). An increase of LDL cholesterol of 1 mg/dl (0.026 mmol/L) is predicted to increase coronary risk by 1% (Mensink & Katan, 1992). In South Africa, 11% of deaths are caused by CVD (WHO, 2011). Mensink and Katan’s (1992) meta-analysis of 27 intervention studies on the effect of dietary fatty acids on serum lipoproteins in humans, found an increase of 1.28 mg/dl of LDL per percent of energy intake, provided by SFAs. However, SFAs do not uniformly affect cholesterol levels. Lauric (C12:0), myristic (C14:0), and palmitic (C16:0), fatty acids lead to increased LDL cholesterol levels, while stearic acid has not been shown to affect total blood cholesterol levels (Hegsted et al., 1965; Grande et al., 1970). A possible explanation for this lack of effect may be due to stearic acid’s rapid conversion to oleic acid, a monounsaturated fatty acid which neither lowers nor increases total cholesterol (Grundy & Denke, 1990). LDL cholesterol levels studied in animal models indicated that LDL levels were raised by lauric, myristic and palmitic acid through the inhibition of the expression of LDL-receptors in the liver. This leads to a decreased removal of circulating LDL (Nicolosi et
al., 1990). Lauric and myristic acids are recommended to contribute less than 10% of total
fat intake (Uauy & Dangour, 2009). Palmitic acid is the most common SFA found in the human diet, followed by stearic, myristic and then lauric acids (Schaefer, 2000). Animal fats are mainly composed of palmitic and stearic acids, while lauric and myristic acids are found in palm kernel and coconut oils (Kris-Etherton & Innis, 2007).
Strategies to decrease the effect of SFA on LDL cholesterol levels have led to studies involving the replacement of SFA with carbohydrates, MUFA or PUFA in the diet (Jakobsen
et al., 2009; Siri-Tarino et al., 2010). Replacement of SFA intake with carbohydrates was
seen to decrease plasma LDL and HDL levels but raise triglyceride levels, without having an effect on weight loss (Siri-Tarino et al., 2010). The use of dietary PUFA in replacing SFA has been found to be the most effective option. It lowers plasma LDL and TC levels through decreasing LDL production rates and/or increasing LDL clearance rates. The HDL:LDL ratio is increased while the TC:HDL ratio decreases (Katan et al., 1994; Siri-Tarino et al., 2010). Dietary MUFA substitution of SFA has been observed to have a similar cholesterol lowering effect as PUFA, however, it does not appear to be as effective (Hodson et al., 2001; Mensink & Katan, 1992). At a recent symposium of the National Lipid Association in 2011, experts reviewed the science on the influence of different fatty acids on CVD during a scientific session. It was reaffirmed that dietary SFA does have an unfavourable influence on LDL levels. New studies, however, on the effects of the replacement of dietary SFA with MUFA and PUFA (LA and EPA/DHA) have some questionable results which will require further research (Baum et al., 2012). The point was made that as food is incredibly complex, it would be incorrect to look only at the outcomes of randomised controlled trials on the replacement of SFA in the diet with other fatty acids, and their influence on CVD. More epidemiological studies also need to be taken into account when making future recommendations (Baum et al., 2012).
Few studies have been done on the effects of dietary fatty acids on cholesterol levels in children. One study by Nicklas et al., (2002) found that dietary fat influences serum lipids in children in a similar way to that of adults. Dietary SFA intake in these children was also shown to be positively associated with total serum cholesterol. Dietary habits in childhood have shown to influence the CVD risk profile in adulthood (Niinikoski et al., 2007). Niinikoski and co-workers (2007) found continuous dietary counselling to be effective in reducing SFA and cholesterol intake in children up to the age of 14 years.
2.4.3 Dietary monounsaturated fatty acid and its role in health
Oleic acid (18:1n9) is the most nutritionally relevant MUFA, with olive and canola oil, avocados, peanuts, pistachios and almonds being dietary sources of oleic acid (Shahidi & Senanayake, 2008). Palmitoleic acid, another MUFA, can be found in certain fish oils and beef fats (Kris-Etherton & Innis, 2007). MUFA is generally liquid at room temperature and solidifies when refrigerated (Kris-Etherton & Innis, 2007). The Mediterranean diet, eaten traditionally by the Greeks, Spanish, French and Italians from the south of Italy, includes a high intake of olives and olive oil. The life expectancy in these areas is higher and the risk of chronic disease, lower (Fung et al., 2009). As olive oil is the main fat consumed in these diets, it has been proposed that MUFA could have a protective effect towards heart disease, diabetes and certain cancers (Bessaoud et al., 2008; Bos et al., 2009; Shahidi & Senanayake, 2008). As previously mentioned, when SFA in the diet is replaced by MUFA, total and LDL plasma cholesterol and total/HDL plasma cholesterol ratio levels are decreased (Bos et al., 2009; Mensink & Katan, 1992; Pérez-Jiménez et al., 2001). In comparing a high carbohydrate diet and a high MUFA diet, plasma triglyceride and LDL levels are decreased and plasma HDL levels are increased in the high MUFA diet (Garg, 2001). Conversely, when MUFA replaces PUFA in the diet, the plasma total and LDL cholesterol are increased (Katan et al., 1994; Kris-Etherton & Yu, 1997). Although evidence of replacing SFA in the diet with MUFA decreases LDL cholesterol is compelling, the associations between MUFA and the end point of CHD is still not as convincing and conclusive (FAO, 2010). In Jakobsen et al., (2009) analysis of 11 cohort studies on the effects of dietary fat on CHD, no associations were found between dietary MUFA and CHD. Epidemiology studies by Posner and co-workers (1991) and Esrey and co-workers (1996), found significant positive associations between CHD and MUFA dietary fat intake in their cohort studies, while the results of the US Nurse’s Health Study showed a significantly negative association (Hu et al., 1997).
Along with the cardiovascular protecting factor observed through the Mediterranean diet, it has also been suggested that MUFA could possibly be associated with a decreased risk of cancer, and breast cancer in particular. Associations between olive oil consumption and reduced breast cancer risk in a dose-response relationship have been observed in many case-controlled studies (Bessaoud et al., 2008; Binukumar & Mathew, 2005). However, it is suggested that the phenolic compound oleuropein found in olive oil is responsible for this reduced risk, its antioxidant properties possibly affecting the initial stage of carcinogenesis (Gerber, 1997). The other characteristics of the Mediterranean diet such as a large intake of fruits and vegetables and a lower intake of animal fats could also possibly influence the cancer risk, confounding the effect of the olive oil (Gerber, 1997). Other studies have,
however, not found any significant associations between MUFA consumption and breast cancer (Binukumar & Mathew, 2005). The relationship between MUFA consumption and cancer is thus inconsistent and inconclusive. Additionally, the source of the MUFA consumed would need to be taken into consideration (FAO, 2010; Gerber, 1997).
Thirdly, there is possible evidence that MUFA could improve insulin sensitivity. Insulin resistance is a significant risk factor in CHD and type two diabetes (FAO, 2010, Pérez-Jiménez et al., 2001). In South Africa, diabetes accounts for 3% of all deaths (WHO, 2011). The insulin sensitivity in 59 healthy subjects was significantly improved after 28 days on an increased MUFA diet (22% of total energy) after an initial SFA enriched diet (Pérez-Jiménez
et al., 2001). Due and co-workers (2008) also observed a significant increase in insulin
sensitivity in non-diabetic obese subjects, after consumption of a high MUFA diet (>20% of energy) compared to a low fat diet for six months. Lovejoy et al. (2002), did not, however, observe any changes in insulin sensitivity in 25 healthy adults on an increased MUFA diet (15% of energy). Results from a similar study by Bos et al. (2009), showed dietary MUFA contributing 20% of the total energy, and supported Lovejoy’s findings. Garg’s (2001) meta-analysis on the affects of a high MUFA diet in type two diabetics in comparison to high carbohydrate diets, also found inconclusive results on dietary MUFA’s effect on insulin sensitivity. More research would need to be done on MUFA’s role in type 2 diabetes and certain cancers, however, there is convincing evidence that the replacement of dietary SFA with MUFA results in a decrease in LDL levels (FAO, 2010).
2.4.4 Dietary polyunsaturated fatty acids and their role in health and development The importance of the EFA, LA and ALA in the diet was first discovered in 1963 when a deficiency was seen in infants fed a skimmed milk-based formula (Hansen et al., 1963). This resulted in the infants’ skin becoming dry, thickened and desquamated. Studies in adults on dietary PUFA, and particularly LA, then focused on its role in CHD and its reduction of plasma risk factors (Kris-Etherton & Innis, 2007). In recent years, studies on the importance of dietary omega-3 fatty acids and their functioning in neurology, their reduction of CHD, inflammation and immune disorders, has gained more attention (Kris-Etherton & Innis, 2007). Omega-6 fatty acids are made up of LA (18:2n-6) derived from sunflower, corn, soybean and safflower oil and ARA (20:4n-6), that are mainly consumed through meat, poultry and eggs. Omega-3 fatty acids are divided into ALA (18:3n-3), EPA (20:5n-3) and DHA (22:6n-3). ALA is obtained through a diet from plant sources: namely flaxseed, canola and soybean oils as well as walnuts. EPA and DHA are mainly obtained from marine sources including fish and crustaceans, particularly fatty fish such as mackerel, herring,
salmon, fresh tuna, trout and oysters as well as algae and omega-3 enriched eggs (Kris-Etherton & Innis, 2007; Tur et al., 2012). LA and ALA are considered parent fatty acids to omega-6 and omega-3 PUFA, as they can be converted to ARA and EPA or DHA, respectively (Hulbert et al., 2005). Inter-conversion of omega-3 and omega-6 PUFA is not possible, making LA and ALA individually essential (Uauy & Dangour, 2009).
Increased PUFA diets are noted as having cardio-protecting effects (Elmadfa & Kornsteiner, 2009). The replacement of SFA with PUFA as previously mentioned has shown to be the most effective way of reducing total and LDL cholesterol, and increasing HDL levels (Mensink & Katan, 1992). TC and LDL cholesterol levels are also decreased when carbohydrates are replaced by PUFA in the diet (Clarke et al., 1997). A nurses’ health study which included 78,778 women, found a significant inverse association between PUFA intake and the risk of CHD (Oh et al., 2005). Findings from Jakobsen and co-workers’ (2009) meta-analysis on cohort studies were in agreement with these findings. Convincing evidence has also been found in clinical controlled studies on the cholesterol lowering effect of dietary PUFA, particularly in comparison to a high SFA diet (Kris-Etherton & Yu, 1997; Mensink & Katan, 1992).
PUFA have also been found to positively influence insulin sensitivity. The exact mechanism of dietary fatty acids’ effects on insulin sensitivity is not fully understood. However, some possibilities may involve the influences of the quality of dietary fatty acids on cell membrane fluidity and functioning. This in turn would influence translocation of glucose, secondary messengers and insulin binding or affinity, ultimately affecting insulin sensitivity throughout the body (Ginsberg et al., 1981). Other possible mechanisms are the direct influence of fatty acids on gene expression and enzyme activity (Clarke, 2004) or the direct effects of fatty acids on insulin-sensitive tissue. In vitro studies have also demonstrated PUFA’s ability to suppress lipogenic gene expression and improve oxidative metabolism (Clarke, 2004). A decrease in insulin sensitivity in the skeletal muscle of 27 patients undergoing coronary artery surgery and 13 healthy adults were both associated with decreased PUFA in skeletal muscle phospholipids; ARA in particular (Borkman et al., 1993). Summers and co-workers (2002) demonstrated that switching from a high SFA diet to a high PUFA diet improved insulin sensitivity which could reduce the risk of developing type 2 diabetes. A cohort study on 43,176 Singaporean Chinese men and women between the ages of 45 to 74 years, reported inverse associations between type 2 diabetes and an increased omega-3 fatty acid intake. The intake of omega-6 and omega-6:omega-3 ratio had no associations with type 2 diabetes (Brostow et al., 2011).
In pregnant and breastfeeding women, the supply of LCPUFA, DHA and ARA from the mother to a developing foetus and infant, particularly during the third trimester and the first postnatal months, is critical (Cetin & Alvino, 2009). During this period the majority of the foetus’s brain, central nervous system and retinoids are developed and DHA and ARA accretion is at a peak. Fifty to sixty per cent of the dry weight of a mammal’s brain is made up of different lipids, of which DHA, ARA and EPA are the majority (De Souza et al., 2011). Inadequate LCPUFA status in a mother, possibly due to malnourishment, multiple pregnancies or a vegetarian diet, could result in an infant being born with a low birth weight and smaller head circumference. Future growth and development could also be affected (Innis, 2007; Ruxton et al., 2007; Schuchardt et al., 2010). The infant’s brain continues to grow rapidly after the first year and a continuing supply of EFA and DHA through the diet or breast milk is necessary. Complementary foods after weaning could, however, be low in DHA, especially in developing countries (Lauritzen & Carlson, 2011). Pregnant women whose diets were supplemented with LCPUFA have shown increases in IQ in their young children; however, this was not seen in infants supplemented with LCPUFA (Protzko et al., 2013).
LCPUFA also influence many of the complex mechanisms involved in the human immune system. Within immune cells, they provide energy as well as physical and functional properties to the cell membrane and influence cellular location and function of proteins. Gene expression is also regulated by LCPUFA and they give rise to eicosanoids such as prostaglandins (PGs), leukotrienes (LTs), lipoxins and resolvins (Calder, 2008). These factors could influence immune cells by affecting membrane order, cell signalling pathways and eicosanoids produced with different biological activities (Calder, 2008). A large quantity of ARA is found in human immune cells but can be altered through an increased intake of dietary EPA and DHA. Phagocytosis, T-cell signalling and antigen presentation capability are all influenced by altering the fatty acid composition of immune cells, which can be done through the diet (Calder, 2008). A correct balance of ARA, EPA and DHA is thus necessary to support immune function (Innis, 2007).
2.4.4.1 Dietary omega-6 fatty acids and their role in health
A shift from the use of saturated fat to plant-based PUFA mainly containing LA was seen in the food industry, which stemmed from previous health recommendations to decrease saturated fat intake (Gibson et al., 2011). It is now, however, a concern of public health officials that high amounts of omega-6 fatty acids are being consumed, particularly in the Western diet, and what effects this may have on human heath (Gibson et al., 2011). Alternatively, it is believed that it is not the increased intake of omega-6 fatty acids that is a
