Maintenance requirement and energetic efficiency of lean and obese Zucker rats.

The body balance technique was used to determine the maintenance requirement and the energetic efficiency of 6-week-old male lean and obese Zucker rats. Fifteen lean and 15 obese rats were assigned to three groups of five each and fed three levels of food intake: ad libitum, 75% of ad libitum, and 50% of ad libitum, for a 4-week period. The obese rats consumed more food and gained significantly more weight than the lean rats. Obese rats utilized dietary energy more efficiently than lean rats but the opposite was true for dietary protein. The efficiency with which obese rats utilized metabolizable energy for gain was 36% compared with efficiency of utilization of metabolizable energy above maintenance for obese and lean were 51.4% and 21.4%, respectively. The maintenance requirement on the basis of metabolic body size for the obese and lean was calculated to be 122 and 130.5 kcal ME per day per kg.75 for the 4-week period. These results indicate that the energetic efficiency is higher in obese than in lean Zucker rats and suggest that the higher energetic efficiency is not the result of a significantly lower maintenance requirement.