1. Nitrogen balance, weight loss and resting metabolic rate were measured in thirty-eight obese inpatients on 3.4 MJ (800 kcal)/d diets over 3 weeks.
2. All subjects were fed on 13% protein-energy in three rneals/d for the first week.
3. In weeks 2 or 3, using a cross-over design, ten subjects were fed on 15 or 10% protein-energy as three meals/d; fourteen subjects were fed on five or one meal/d with 13%protein energy; and fourteen subjects were fed on 15% protein-energy as five meals/d or 10% protein-energy as one meal/d.
4. N loss was least on the high-protein week and frequent-meal week: the largest difference was found when these effects were combined (P < 0.001).
5. When protein-energy was held constant at 13% N loss decreased significantly (P < 0.01) between week 2 and 3, but when the protein-energy was manipulated there was no significant N conservation in the third week. This suggests that the protein:energy value is more important than meal frequency in the preservation of lean tissue.
6. Weight loss was also least on the ‘high-protein’ week and ‘frequent-meal’ week, but this result reached significance only when the effects were combined (P < 0.05).
7. Resting metabolic rate decreased with time but was not significantly altered by the dietary regimens.
8. Therefore, during the first 3 weeks at an intake of 3.4 MJ/d, a diet with a high-protein concentration, fed as frequent small meals, is associated with better preservation of lean tissue than an isoenergetic diet with lower-protein concentration fed as fewer meals. There was no evidence that meal frequency or protein concentration affect the rate of fat loss.
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