Insulin resistance and the metabolic syndrome in obese black South African women : a focus on risk factors

Thesis (Ph.D. (Dietetics))--North-West University, Potchefstroom Campus, 2005.Introduction: High rates of obesity occur in black South African women, up to double the rate in whites. Concern about the potential health burden of obesity in these women as well as a lack of understanding of the underlying mechanisms of obesity, motivated the POWIRS study (Profiles of Women with the Insulin Resistance Syndrome). Subjects and methods: The study population consisted of 100 urbanised black women of the North-West Province, South Africa. These women were recruited as apparently healthy, non-pregnant selected volunteers, with ages of 19 to 50 years. Using a cross-sectional comparative study design, the women were divided into a normal-weight, overweight and obese group. Relevant demographic, anthropometric, dietary intake, and serum and plasma variables associated with the metabolic syndrome were compared in these three groups. Descriptive statistics, partial Spearman correlations, odds ratios and effect sizes were calculated. A medium effect size (d ≥ 0.5) indicated possible practical significance, while a large effect size (d ≥ 0.8) indicated practical significance. Results: The acute-phase proteins serum (s)- C-reactive protein, plasma (p)-fibrinogen and possibly p-plasminogen activator inhibitor-I (PAI-1) had practical significantly higher levels in the obese than the normal-weight women. High-risk levels of s- C-reactive protein (≥ 3 mglL) occurred in 68% of the obese women compared to 16% of the normal-weight women. Increased p-PAI-1 levels (> 7 U/ml) occurred in 46% of the obese compared to 24% of the normal-weight women. Of the metabolic syndrome components, s-C-reactive protein showed the strongest correlation with body mass index (r = 0.60, p < 0.0001). Metabolic syndrome components s-uric acid, s-fasting glucose, s-2h-post-load glucose, s-fasting insulin and the HOMA-insulin-resistance index had practical significantly higher levels in the obese than the normal-weight women, while systolic and diastolic blood pressure, s-gamma-glutamyl-transferase (GGT) and s-triglycerides had higher levels indicative of practical significance (d ≥ 0.5). The metabolic syndrome was diagnosed in 38% of the obese women, 8% of the overweight women and in none of the normal-weight women. The acute-phase protein s-C-reactive protein, but not p-fibrinogen and p-PAI-1, had higher levels indicative of practical significance in women with compared to those without the metabolic syndrome. Serum-C-reactive protein and p-PAI-1 were positively associated with the HOMA-insulin-resistance index (r = 0.25, p < 0.05 and r = 0.22, p < 0.05, respectively). After exclusion of dietary under-reporters, the obese women compared to the normal-weight women had practical significantly higher daily intakes of the following: total energy (10 591 versus 8 419 kJ), total carbohydrates (311 g versus 257 g), total protein (97 g versus 69 g), animal protein (62 g versus 40 g), total fat (86 g versus 66 g), saturated fat (28 g versus 21 g) and dietary fibre (22 g versus 17 g). A high frequency of overeating incidents (38 - 59%) and emotion-induced eating (48%) occurred in women of all body-weight groups, probably representing barriers to successful weight control. Therefore, emotion-induced eating may be a possible risk factor for the development of obesity and a factor in the maintenance thereof in this population group. Attitudes towards weight control and thinness did not differ practical significantly between the three groups of women. However, with increasing body mass index more women had a positive attitude towards thin people. None of the women had a negative attitude towards thin people and weight control. Obese women had better knowledge (d ≥ 0.5) of the relationship between obesity, nutrition and health than the normal-weight women. The majority of the obese women (87%), 81% of the overweight and 12% of the normal-weight women indicated that they should lose weight. Forty-five percent of the obese women, 44% of the overweight women and 16% of the normalv weight women had been on weight reducing diets before. At the time of the study, 71% of the obese, 60% of the overweight and 11% of the normal-weight women indicated that they were currently trying to lose weight. Conclusions: In a group of 100 urbanised black women of the North-West Province, South Africa, levels of the acute-phase proteins C-reactive protein, fibrinogen and possibly PAI-1, were practical significantly higher in obese than normal-weight women. C-reactive protein, but not fibrinogen and PAI-1 may be part of the metabolic syndrome in these women. Since prospective studies have shown that C-reactive protein, PAI-1 and fibrinogen are predictors of myocardial infarction, stroke and non-insulin-dependent diabetes mellitus (NIDDM), this study indicates that obesity may lead to an increased health risk in this population. The women in this study had a more Westernised attitude towards body size and weight control, which could improve compliance with weight control programmes. However, the barriers to successful weight control in these women should be addressed, for example emotion-induced eating. Since the obese women had better knowledge of the relationship between obesity, nutrition and health than the normal-weight women, lack of knowledge may not represent a barrier to successful weight control in these women. Recommendations: It is recommended that the dietary analysis should be repeated in a larger sample of women. These results should motivate urgent development of culturally-sensitive weight control programmes for obese African women. Such programmes could prevent an enormous burden due to obesity and its health consequences on public health resources of this country in the decades to come. Further research of the underlying mechanisms leading to obesity in this population group is strongly recommended, especially the role of emotion-induced eating.Doctora