Low plasma leptin concentration and low rates of fat oxidation in weight-stable post-obese subjects.

OBJECTIVE: A low resting metabolic rate for a given body size and composition, a low rate of fat oxidation, low levels of physical activity, and low plasma leptin concentrations are all risk factors for body weight gain. The aim of the present investigation was to compare resting metabolic rate (RMR), respiratory quotient (RQ), levels of physical activity, and plasma leptin concentrations in eight post-obese adults (2 males and 6 females; 48.9 +/- 12.2 years; body mass index [BMI]: 24.5 +/- 1.0 kg/m2; body fat 33 +/- 5%; mean +/- SD) who lost 27.1 +/- 21.3 kg (16 to 79 kg) and had maintained this weight loss for > or =2 months (2 to 9 months) to eight age- and BMI-matched control never-obese subjects (1 male and 7 females; 49.1 +/- 5.2 years; BMI 24.4 +/- 1.0 kg/m2; body fat 33 +/- 7%). RESEARCH METHODS AND PROCEDURES: Following 3 days of weight maintenance diet (50% carbohydrate and 30% fat), RMR and RQ were measured after a 10-hour fast using indirect calorimetry and plasma leptin concentrations were measured using radioimmunoassay. Levels of physical activity were estimated using an accelerometer over a 48-hour period in free living conditions. RESULTS: After adjustment for fat mass and fat-free mass, post-obese subjects had, compared with controls, similar levels of physical activity (4185 +/- 205 vs. 4295 +/- 204 counts) and similar RMR (1383 +/- 268 vs. 1430 +/- 104 kcal/day) but higher RQ (0.86 +/- 0.04 vs. 0.81 +/- 0.03, p < 0.05). Leptin concentration correlated positively with percent body fat (r = 0.57, p < 0.05) and, after adjusting for fat mass and fat-free mass, was lower in post-obese than in control subjects (4.5 +/- 2.1 vs. 11.6 +/- 7.9 ng/mL, p < 0.05). DISCUSSION: The low fat oxidation and low plasma leptin concentrations observed in post-obese individuals may, in part, explain their propensity to relapse.

[Heart rate and physical activity to assess energy expenditure in children]. / Medicion del gasto energetico en niños a partir de la frecuencia cardiaca y actividad.

The aim of the present study was to validate assessment of oxygen consumption (VO2) from heart rate (HR) and physical activity (PA) electronically recorded. Every minute, mean VO2 were validated with indirect calorimetry. We studied 25 children (12 girls, 13 boys), 12.1 +/- 0.7 years old. Measurements were made during about 60 minutes while kids were supine, sitting, standing and walking at four intensities. Minute by minute heart rate was converted to VO2 and energy expenditure using 2 different functions for active and inactive situations. A linear function (VO2 = a + beta HR) was used when counts were 7 or higher and HR higher than a prefixed point (intersection between the 2 line functions). A nonlinear equation (VO2 = a + beta HR3) was used in the remaining minutes. Mean predicted VO2 for every minute were similar to measured VO2 (2 ways interaction ANOVA, p = 0.99). Mean VO2 correlated significantly with VO2 predicted by equation (r = 0.99, p < 0.01). High degree of agreement was found (Bland-Altman comparisons). Combined heart rate and physical activity predicted oxygen consumption with a precision similar to the indirect calorimetric method.