Energy expenditure mechanisms in obesity : a comparison of subjects who gain weight easily and with difficulty

The purpose of this study wes to make a systematic evaluation and comparison of two groups of subjects: a group who claimed to gain weight readily without consuming excessive calories and a group who claimed to be able to eat freely and have no problem with weight gain. Each subject completed a dietary and weight history, a physical activity history, and seven-day food and physical activity records.

A decreased efficiency for coupling energy production to muscular contraction could be responsible for the imbalance in the energy equation for some subjects. To investigate this possibility, mechanical efficiency was measured in the two groups of subjects. Each subject completed a series of submaximal work rates on a cycle ergometer and treadmill. For the bicycle tests, the beginning work rate was 29.4 watts for 10 minutes, followed by work rate increments of 29.4 watts for each subsequent test. For the treadmill tests, subjects walked at 100 meters per minute at zero percent grade for ten minutes, followed by subsequent two percent increases in grade. Expired gas samples, collected during the last four minutes of each ten minute test, were used to calculate oxygen uptake.

There were no significant differences in gross efficiency between the two groups of subjects for either bicycle or treadmill exercise. For both forms of exercise, efficiency increased significantly with increases in work rate. These results can be explained as an artifact of the calculation since with increasing work, the resting caloric expenditure becomes a smaller fraction of the total caloric expenditure.

The purposes of the second part of this study were to determine if differences existed in the resting metabolic rates of the two groups and to investigate the role of the sympathetic nervous system in these differences. Resting metabolic rates were measured 30 minutes prior to and 30 minutes following ingestion of 80 mg of propranolol. Oxygen consumption was measured and expressed per kg body weight. There were no significant differences between the two groups for resting metabolic prior to taking the drug. Ingesting 80 mg propranolol had no significant effect on resting metabolic rate in either group.