Determinants of body composition changes over 5.5 years and the associated cardio-metabolic risk factors in free-living black South African women

Master Thesis


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University of Cape Town

Research from both developed and developing countries, including South Africa (SA), has shown that black women experience a disproportionately high burden of obesity and associated non-communicable diseases compared to their white counterparts. To our knowledge, there are no longitudinal studies that have examined the determinants of obesity and the associated cardio-metabolic risk factors in black SA women. The overall aim of this thesis was to examine the determinants of the changes in body composition and the associations with cardio-metabolic risk factors over a 5.5-year follow-up period in a cohort of free-living black SA women. These aims were addressed in two separate chapters with the following specific aims: Chapter 1: To examine changes in body weight, body composition and body fat distribution over 5.5-years in relation to changes in cardio-metabolic risk factors; Chapter 2: To examine the modifiable and non-modifiable determinants of the changes in body weight and body fat distribution over the follow-up period. A convenience sample of 64 apparently healthy black SA women (26±7 years) were tested at baseline and again after approximately 5.5-years. Testing included measuresof body composition and body fat distribution (dual-energy x-ray absorptiometry and computerised tomography), blood pressure, fasting glucose, insulin and lipid concentrations.An oral glucose tolerance test was performed at follow-up only, from which insulin sensitivity(Matsuda index) and secretion (insulinogenic index) were calculated. In addition, participants completed questionnaires to assess socio-economic status (SES) and lifestyle factors including reproductive health at baseline and follow-up. Physical activity (Global Physical Activity Questionnaire) and dietary intake (Quantified Food Frequency questionnaire) were reported at baseline only. Chapter 1: There was a significant increase in body weight (8.8±12.5%) and total fat mass (16.4±26.9%), and all other measures of body fat distribution (range: 1.4–35.1%). When expressed relative to total fat mass (%FM), there was an increase in trunk fat mass with a concomitant decrease in peripheral fat mass, which was associated with increased fasting glucose concentrations and reduced insulin sensitivity, and a compensatory increase in insulin secretion at follow-up. Chapter 2: The increase in body weight was associated with a lower baseline body mass index (BMI), being nulliparous at baseline, and not having children over the follow-up period. Sanitation at baseline and change in sanitation over time had opposing effects on body weight, with smaller increases in weight in those women who had access to sanitation at baseline and larger increases in weight seen in those who improved sanitation over the follow-up period. Centralisation of body fat was associated with a lower BMI and being nulliparous at baseline only. Being younger at baseline was also associated with larger increases in body weight and centralisation of fat mass, but was not independent of the other variables. In a sample of free-living black SA women, body weight (~9%) and fat mass (~17%) increased significantly over a 5.5-year follow-up period. These increases, and specifically the increase in central fat mass, were associated with increased fasting glucose concentrations and reduced insulin sensitivity. When examining the determinants of weight gain and increasing centralisation of fat mass, younger women without children, with a lower BMI, were at greatest risk of increased weight gain, and should be the target of future interventions in this population. The risk of weight gain was further mediated by changes in SES, which should be examined further.

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