METABOLIC RESPONSES TO ISOENERGETIC MEALS CONTAINING DIFFERENT PROPORTIONS OF CARBOHYDRATE AND FAT

The purpose of the present study was to investigate the interrelations hip between carbohydrate and fat metabolism at rest after isoenergetic meals of varying proportions of carbohydrate and fat, Eight physicall y-active subjects (BMI 18.1-23.4 kg/m(2)) were studied at rest on thre e occasions after an overnight fast. In a balanced design they were gi ven meals containing carbohydrate, protein and fat in the following am ounts respectively (g/70 kg body weight): meal 1 121, 16, 48; meal 2 7 0, 16, 70; meal 3 50, 14, 80. All meals were isoenergetic, containing 4.0 MJ/70 kg body weight, and were of similar appearance. In addition, on a fourth occasion five of the eight subjects consumed meal 4 (g/70 kg body weight): carbohydrate 0, protein 0, fat 108. Blood samples we re taken before eating the meal and at intervals following the meal to determine metabolic and hormonal responses. Energy expenditure and su bstrate oxidation were measured by indirect calorimetry and balance wa s calculated over the 5 h postprandial period. The incremental areas u nder the time curves for fat oxidation were greatest after meals 3 and 4 (P < 0.05), whereas incremental areas under the carbohydrate oxidat ion v. time curves were relatively reduced after these two meals (P < 0.05). This was accompanied by lesser suppression of plasma non-esteri fied fatty acid concentrations (P < 0.001) and reduced plasma insulin concentrations (P < 0.001) following these meals. Energy balance was a lmost identical after the three isoenergetic meals. In contrast, there was an inverse relationship between carbohydrate and fat balance foll owing these meals, with carbohydrate balance decreasing as carbohydrat e intake decreased and fat balance increasing as fat intake increased. We conclude that there is a close interrelationship between carbohydr ate and fat metabolism following isoenergetic meals in resting subject s.