Dietary and plasma fatty acids in association with obesity in black South Africans
Background South Africa is currently experiencing rapid nutritional, economic, demographic and epidemiological transitions with grave consequences for lifestyle and health. Obesity has escalated to epidemic levels and is a significant risk factor for metabolic syndrome (MetS) and cardiovascular disease. The increasing prevalence of obesity and related risk factors is compounded by the increased fat intake observed in many countries in Africa. Research reports and findings indicate that specific dietary and circulating fatty acids (FAs) as well as subsequent FA patterns may be beneficial or detrimental to human health. Despite the extensive use of circulating FAs in research in Asia, Europe and the USA, there is limited epidemiological research on the association of dietary FAs and circulating FA with obesity and MetS in black populations in Africa. Aim The PhD study aimed to investigate the association of dietary FAs and plasma phospholipid FAs and FA patterns with obesity and MetS, as well as comparison of dietary FAs and plasma phospholipid FAs in metabolically healthy and unhealthy phenotypes in a selected group of black South Africans. This study forms part of the South African arm of the international Prospective Urban and Rural Epidemiological (PURE) study. Subjects and methods The study sample consisted of 711 (273 men and 438 women) adults; a sub-cohort of apparently healthy black men and women aged 30 to 93 years, from the rural and urban areas of the North West Province, South Africa. A random sample was selected from the original 2010 volunteers with both dietary and plasma phospholipid FAs after exclusion of 305 participants with human immunodeficiency virus and 305 matched controls due to previous use of plasma for analysis. The number of participants was randomly selected from stratified groups (rural male, rural female, urban male, and urban female. The sample included 125 rural men, 148 urban men, 218 rural women and 220 urban women. All the participants gave written and informed consent at each follow-up. The Ethics Committee of the North-West University approved the South African PURE study (Ethics number 04M10) and additional ethical clearance for this affiliated PhD study (NWU-00346-16-S1). This PhD study include two cross-sectional studies and one longitudinal study of the 711 participants. The first cross-sectional study compared the levels of dietary and plasma phospholipid FAs of metabolically healthy and unhealthy phenotypes. The second study cross-sectionally investigated the association of dietary and plasma phospholipid FAs patterns with measures of adiposity including, body mass index (BMI), waist circumference (WC), and waist: height ratio (WHTR) and MetS. The third study prospectively investigated the association of baseline plasma phospholipid FA patterns with 10-year changes in anthropometric indices (weight, BMI, WC, and WHtR), as well as the reproducibility of plasma FA patterns at the 10-year time point. This study included 412 (173 men and 275 women) of 711 participants, followed up for 10 years and with complete anthropometric and plasma phospholipid FA data at baseline and follow-up. Results Study I: Adults from the South African arm of the Prospective Urban and Rural Epidemiology study (n=711) were categorised into four groups, namely normal weight without metabolic syndrome (MetS) (MHNW), normal weight with MetS (MUNW), metabolically healthy overweight/obese (MHO) and metabolically unhealthy overweight/obese (MUO). Dietary and plasma phospholipid FAs were measured by a quantitative food frequency questionnaire and gas chromatography-tandem mass spectrometry respectively. MetS was present in 35% of the participants. Compared to the MHNW reference group, dietary saturated FAs (C14:0 to C18:0) and alpha-linoleic acid intakes were higher in both overweight/obese groups (MHO and MUO), while most mono-unsaturated FAs (MUFAs), linoleic and arachidonic acid intakes were higher in the MUO group only. Plasma levels of most very long chain saturated FAs (C18:0 to C22:0) and PUFAs were higher, whereas selected MUFAs, palmitic acid and estimated desaturase activities were lower in the overweight/obese groups after adjustment for age and total energy intake. Study II: Two patterns were derived from dietary FAs and six patterns from plasma phospholipid FAs, which explained the cumulative variance of 89% and 73%, respectively. The association between FA patterns with adiposity and MetS, respectively, was weaker for dietary FA patterns than for plasma phospholipid FA patterns. The plasma phospholipid FA pattern with high loadings of saturated FAs (SFAs) (high-Satfat) and another with high loadings of n—3 very long chain PUFAs (n—3 VLC-PUFA) were positively associated with measures of adiposity and MetS, while patterns with positive loadings of n—9 long chain monounsaturated fatty acids (n—9 LC-MUFA) and positive loading of n—3 essential FA (n—3 EFA) showed inverse associations with MetS and some measures of adiposity. Study III: Six plasma phospholipid FAs patterns were identified at baseline and four similar FA patterns were identified at follow-up. A comparison of quartiles of factor scores at baseline and follow-up showed good reproducibility for four of the six FA patterns identified at baseline. The high-Satfat pattern presented with high positive loadings of saturated FAs (stearic, arachidic, behenic and lignoceric acids) both at baseline and 10-year follow-up, and was positively associated with 10-year changes in all anthropometric outcomes. This pattern that was maintained over 10 years may indicate unique FA metabolism associated with weight gain over time in this group of black South African adults. At 10-year follow-up plasma phospholipid levels of SFAs, stearic, arachidic and behenic acids were higher in overweight/obese participants of both sexes, confirming the association between plasma VLC-SFAs and adiposity. The baseline n—9 LC-MUFA pattern, with positive loadings of MUFAs (nervonic and gondoic acid), was positively associated with 10-year increases in all anthropometric outcomes, but this pattern was not maintained over 10 years. Most of the plasma MUFAs, notably nervonic and gondoic acid decreased significantly over ten years, while BMI, waist circumference and WHtR increased. Therefore, a sustained positive association between n-9 LC-MUFAs and adiposity could not be confirmed. Conclusion The results from this study show that overweight groups generally had higher fat intakes than normal weight (MHNW and MUNW) groups. The lower plasma levels of de novo lipogenesis pathway FAs and estimated desaturase activities may be biomarkers of abnormal metabolic health in overweight/obese study participants. In dimension reduction analysis, the n–9 LC-MUFA and n—3 EFA patterns seem to provide possible protective associations with adiposity and MetS, whereas the high-Satfat and n—3 VLC-PUFA patterns were associated with adiposity and MetS in our study participants in the cross-sectional study. In the longitudinal study, both the baseline n-9 LC-MUFA pattern and the high-Satfat pattern were associated with adiposity gain over 10 years. The high-Satfat pattern may be indicative of dietary intake and de novo lipogenesis involving elongation of FAs and was associated with adiposity gain over 10 years. This pattern derived at baseline was reproducible in the study participants after 10 years and may indicate a unique FA metabolism. On the other hand, the n-9 LC-MUFA pattern was not sustained over 10 years, thus a conclusion of an association between this FA pattern and adiposity gain cannot be made. This publication adds to the understanding of plasma phospholipid FA patterns and their prospective associations, as well as the reproducibility of some of these patterns. Further work is required to improve the interpretation and application of circulating FA patterns in health and disease globally, but especially in Africa, where data are lacking.
- Health Sciences