Weight-related differences in glucose metabolism and free fatty acid production in two South African population groups

OBJECTIVE: The effects of free fatty acids (FFA), leptin, tumour necrosis f actor (TNF) alpha and body fat distribution on in vivo oxidation of a gluco se load were studied in two South African ethnic groups. DESIGN AND MEASUREMENTS: Anthropometric and various metabolic indices were measured at fasting and during a 7h oral glucose tolerance test (OGTT). Bod y composition was measured using bioelectrical impedance analysis and subcu taneous and visceral fat mass was assessed using a five- and two-level CT-s can respectively. Glucose oxidation was evaluated by measuring the ratio of (CO2)-C-13 to (CO2)-C-12 in breath following ingestion of 1-C-13-labelled glucose. SUBJECTS: Ten lean black women (LBW), ten obese black women (OBW), nine lea n white women (LWW) and nine obese white women (OWW) were investigated afte r an overnight fast. RESULTS: Visceral fat levels were significantly higher (P < 0.01) in obese white than black women, despite similar body mass indexes (BMIs). There wer e no ethnic differences in glucose oxidation however; in the lean subjects of both ethnic groups the area under the curve (AUC) was higher than in obe se subjects (P < 0.05 for both) and was found to correlate negatively with weight (r = -0.69, P < 0.01) after correcting for age. Basal TNF alpha conc entrations were similar in all groups. Percentage suppression of FFAs at 30 min of the OCTT was 24 +/- 12% in OWW and - 38 +/- 23% (P < 0.05) in OBW, ie the 30 min FFA level was higher than the fasting level in the latter gro up. AUC for FFAs during the late postprandial period (120 - 420 min) was si gnificantly higher in OWW than OBW (P < 0.01) and LWW (P < 0.01) and correl ated positively with visceral fat mass independent of age (r = 0.78, P < 0. 05) in the OWW only. Leptin levels were higher (P < 0.01) both at fasting a nd during the course of the OCTT in obese women from both ethnic groups com pared to the lean women. CONCLUSIONS: Glucose oxidation is reduced in obese subjects of both ethnic groups; inter- and intra-ethnic differences were observed in visceral fat m ass and FFA production and it is possible that such differences may play a role in the differing prevalences of obesity-related disorders that have be en reported in these two populations.