Objective: A low-fat, high-carbohydrate diet (</=30% of total energy intake as fat) in conjunction with moderate intensity physical activity is widely recommended for weight maintenance and reduction. The aim of this study was to assess the effect of adding daily exercise to a short-term high-carbohydrate diet on fasting and postprandial leptin levels.
Subjects: Eight healthy, postmenopausal women aged 60+/-4 y (mean+/-s.d.) (body mass index, BMI: 26.4+/-2.3 kg m(-2); predicted maximal oxygen uptake: 29+/-2 ml kg(-1) min(-1)).
Design: Plasma responses were studied after subjects consumed the same high-fat, mixed meal on three occasions: after 3 days on a low-carbohydrate diet (35, 50 and 15% energy from carbohydrate, fat and protein, respectively) (Low-CHO); after 3 days on an isoenergetic high-carbohydrate diet (corresponding values 70, 15 and 15%) (High-CHO); and after 3 days on the same high-carbohydrate diet with 60 min of brisk walking daily (High-CHO-Ex).
Measurements: Fasting and postprandial plasma or serum concentrations of leptin, glucose and insulin.
Results: Fasting leptin was significantly higher (P<0.05) after the High-CHO (18.4+/-2.6 ng ml(-1)) (mean+/-s.e.m.) than after both the Low-CHO and the High-CHO-Ex interventions, which did not differ significantly from each other (16.9+/-2.1 and 15.5+/-2.0 ng ml(-1), respectively; P=0.08). Overall (fasted and postprandial states), plasma leptin concentrations were significantly higher after the High-CHO than after the High-CHO-Ex intervention. There was a strong, positive, linear relation between postprandial insulin responses and postprandial leptin concentrations at 6 h. In addition, there was a strong, negative, linear relation between whole-body insulin sensitivity (based on postprandial responses of glucose and insulin) and postprandial leptin concentrations at 6 h.
Conclusion: Daily moderate intensity exercise, without concomitant changes in body fat mass, suppressed fasting and postprandial circulating leptin concentrations after consumption of a short-term high-carbohydrate diet. As shown in previous studies, insulin appears to be an important modulator of leptinaemia.