Evidence for a long time course adaptation of glucose metabolism to high protein feeding in rats without changes in resting energy expenditure

Abstract

High protein (HP) diet decreases spontaneous energy intake in rat. This effect has been suspected to be associated to an increased thermic effect of feeding (TEF). We evaluate the changes of energy expenditure and nutrient oxidation occurring during the adaptation to a HP diet. For that purpose 48 Wistar rats were fed a normal protein (NP) diet for 1 week and then a HP diet. Energy metabolism was measured in an open circuit indirect calorimetry after 1, 3, 6 or 15 d. After fasting overnight, they received a calibrated meal of 4 g. The postprandial metabolism was followed for 4 h. During the fasting state, total but not resting energy expenditure (REE) tended to increase in HP groups (p=0.06). Activity differed among groups with a trend to increase from 1 to 6 d of HP diet. Compared to NP, TEF increased as soon as the second day of HP diet and was the highest after 6 d. During fasting, there was a trend to a lower fat oxidation after 3 d of HP diet, at the expense of protein oxidation. In the fed state, fat oxidation increased after 1 d of HP diet but then decreased after 3 d. Interestingly, CHO oxidation was twice lower after 1 d of HP diet and then progressively increased until 15 d but remained lower than in NP rats. We showed that TEF and activity but not REE were enhanced by the HP diet. This also led to dramatic changes in postprandial nutrient oxidation and suggested a slow adaptation of CHO metabolism from 3 to 15 d.