Substrate oxidation during exercise: impact of time interval from the last meal in obese women.

OBJECTIVE

To investigate whether time interval between meal and exercise alters the balance of substrate oxidation during an exercise bout.

HYPOTHESIS

Exercise performed 3-h after meal induces a higher rate of lipid oxidation than when performed only 1-h after meal.

RESEARCH METHODS AND PROCEDURES

Eight overweight and obese postmenopausal women (age: 57.4+/-2.4 y; BMI: 31.8+/-2.1 kg m(-2); %FAT: 42.7+/-1.2%, mean+/-s.e.m.) performed two sessions of exercise training at an intensity corresponding to their ' crossover' point of substrate oxidation (COP(ox)). One session was held 1 h after a standardized meal and the other, 3 h after an identical meal on another day. Substrate oxidation was evaluated by indirect calorimetry. Hormonal responses were investigated during exercise.

RESULTS

Respiratory exchange ratio values were lower in the 3-h condition, showing higher lipid oxidation during exercise (average difference+38.9+/-2.7 mg min(-1); P<0.001), while mean energy expenditure did not differ. Basal heart rate was reduced in the 3 h compared with the 1-h condition (78+/-5 vs 87+/-5 bpm; P<0.05). Glycemia, lactatemia and insulinemia were reduced when exercise was performed 3 h after meal (P<0.05).

DISCUSSION

When exercise is performed 3 h after meal at an intensity corresponding to the COP(ox), metabolic and hormonal responses are similar to those targeted during the submaximal exercise test performed at fast that we previously proposed to individualize exercise training in the obese.