Visceral adipose tissue (VAT) is associated with adverse health effects including cardiovascular disease and type 2 diabetes. We developed a dual‐energy X‐ray absorptiometry (DXA) measurement of visceral adipose tissue (DXA‐VAT) as a low cost and low radiation alternative to computed tomography (CT). DXA‐VAT was compared to VAT assessed using CT by an expert reader (E‐VAT). In addition, the same CT slice was also read by a clinical radiographer (C‐VAT) and a best‐fit anthropomorphic and demographic VAT model (A‐VAT) was developed. Whole body DXA, CT at L4–L5, and anthropometry were measured on 272 black and white South African women (age 29 ± 8 years, BMI 28 ± 7 kg/m², waist circumference (WC) 89 ± 16 cm). Approximately one‐half of the dataset (n = 141) was randomly selected and used as a training set for the development of DXA‐VAT and A‐VAT, which were then used to estimate VAT on the remaining 131 women in a blinded fashion. DXA‐VAT (r = 0.93, standard error of the estimate (SEE) = 16 cm²) and C‐VAT (r = 0.93, SEE = 16 cm²) were strongly correlated to E‐VAT. These correlations with E‐VAT were significantly stronger (P < 0.001) than the correlations of individual anthropometry measurements and the A‐VAT model (WC + age, r = 0.79, SEE = 27 cm²). The inclusion of anthropometric and demographic measurements did not substantially improve the correlation between DXA‐VAT and E‐VAT. DXA‐VAT performed as well as a clinical read of VAT from a CT scan and better than anthropomorphic and demographic models.

Objective: To investigate body composition differences, especially the relationship between body mass index (BMI) and percent body fat (%BF), among five ethnic groups. Design: Cross-sectional. Subjects: Seven hundred and twenty-one apparently healthy women aged 18–60 years (BMI: 17.4–54.0 kg/m²) from South Africa (SA, 201 black, 94 European) and New Zealand (NZ, 173 European, 76 Maori, 84 Pacific, 93 Asian Indian). Measurements: Anthropometry, including waist circumference, and total, central and peripheral body fat, bone mineral content and total appendicular skeletal muscle mass (ASMM) derived from dual X-ray absorptiometry. Results: Regression analysis determined that at a BMI of 30 kg/m², SA European women had a %BF of 39%, which corresponded to a BMI of 29 for SA black women. For a BMI of 30 kg/m² in NZ Europeans, equivalent to 43% body fat, the corresponding BMIs for NZ Maori, Pacific and Asian Indian women were 34, 36 and 26 kg/m², respectively. Central fat mass was lower in black SA than in European SA women (P<0.001). In NZ, Pacific women had the lowest central fat mass and highest ASMM, whereas Asian Indian women had the highest central fat mass, but lowest ASMM and bone mineral content. Conclusions: The relationship between %BF and BMI varies with ethnicity and may be due, in part, to differences in central fatness and muscularity. Use of universal BMI or waist cut-points may not be appropriate for comparison of obesity prevalence among differing ethnic groups, as they do not provide a consistent reflection of adiposity and fat distribution across ethnic groups.

We examined the variability and determinants of the respiratory exchange ratio (RER) at rest and during exercise in 61 trained cyclists. Fasting (10–12 h) RER was measured at rest and during exercise at 25, 50, and 70% of peak power output (W_peak), during which blood samples were drawn for [lactate] and [free fatty acid] ([FFA]). Before these measurements, training volume, dietary intake and muscle fiber composition, [substrate], and enzyme activities were determined. There was large interindividual variability in resting RER (0.718–0.927) that persisted during exercise of increasing intensity. The major determinants of resting RER included muscle glycogen content, training volume, proportion of type 1 fibers, [FFA] and [lactate], and %dietary fat intake (adjusted r²= 0.59, P < 0.001). Except for muscle fiber composition, these variables also predicted RER at 25, 50, and 70% W_peakto different extents. The key determinant at 25% W_peakwas blood-borne [substrate], at 50% was muscle [substrate] and glycolytic enzyme activities, and at 70% was [lactate]. Resting RER was also a significant determinant of RER at 25 ( r = 0.60) and 50% ( r = 0.44) W_peak.

Background:Subjects exercising without fluid ingestion in desert heat terminated exercise when the total loss in body weight exceeded 7%. It is not known if athletes competing in cooler conditions with free access to fluid terminate exercise at similar levels of weight loss.Objectives:To determine any associations between percentage weight losses during a 224 km Ironman triathlon, serum sodium concentrations and rectal temperatures after the race, and prevalence of medical diagnoses.Methods:Athletes competing in the 2000 and 2001 South African Ironman triathlon were weighed on the day of registration and again immediately before and immediately after the race. Blood pressure and serum sodium concentrations were measured at registration and immediately after the race. Rectal temperatures were also measured after the race, at which time all athletes were medically examined. Athletes were assigned to one of three groups according to percentage weight loss during the race.Results:Body weight was significantly (p<0.0001) reduced after the race in all three groups. Serum sodium concentrations were significantly (p<0.001) higher in athletes with the greatest percentage weight loss. Rectal temperatures were the same in all groups, with only a weak inverse association between temperature and percentage weight loss. There were no significant differences in diagnostic indices of high weight loss or incidence of medical diagnoses between groups.Conclusions:Large changes in body weight during a triathlon were not associated with a greater prevalence of medical complications or higher rectal temperatures but were associated with higher serum sodium concentrations.

The aim of this study was to investigate the effect of a high-fat diet (HFD) followed by 1 day of carbohydrate (CHO) loading on substrate utilization, heart rate variability (HRV), effort perception [rating or perceived exertion (RPE)], muscle recruitment [electromyograph (EMG)], and performance during a 100-km cycling time trial. In this randomized single-blind crossover study, eight well-trained cyclists completed two trials, ingesting either a high-CHO diet (HCD) (68% CHO energy) or an isoenergetic HFD (68% fat energy) for 6 days, followed by 1 day of CHO loading (8–10 g CHO/kg). Subjects completed a 100-km time trial on day 1 and a 1-h cycle at 70% of peak oxygen consumption on days 3, 5, and 7, during which resting HRV and resting and exercising respiratory exchange ratio (RER) were measured. On day 8, subjects completed a 100-km performance time trial, during which blood samples were drawn and EMG was recorded. Ingestion of the HFD reduced RER at rest (P < 0.005) and during exercise (P < 0.01) and increased plasma free fatty acid levels (P < 0.01), indicating increased fat utilization. There was a tendency for the low-frequency power component of HRV to be greater for HFD-CHO (P = 0.056), suggestive of increased sympathetic activation. Overall 100-km time-trial performance was not different between diets; however, 1-km sprint power output after HFD-CHO was lower (P < 0.05) compared with HCD-CHO. Despite a reduced power output with HFD-CHO, RPE, heart rate, and EMG were not different between trials. In conclusion, the HFD-CHO dietary strategy increased fat oxidation, but compromised high intensity sprint performance, possibly by increased sympathetic activation or altered contractile function.