Meal palatability, substrate oxidation and blood glucose in young and older men

We investigated the effects of food palatability on the thermic effect of feeding (TEF), substrate oxidation and circulating glucose and insulin. Healthy young men (23.4+/-1.0, SD, years, n=10) and older men (69.4+/-1.3, years, n=9) were resident in a metabolic unit for two 2-day study periods. On the second day of each period, they consumed in random order either a palatable test meal containing 2.93 MJ or a nonpalatable control meal containing the same foods in identical amounts but blended and freeze-dried into biscuit form. TEF and respiratory quotient (RQ) were measured over 6 h and blood samples were taken for measurement of glucose and insulin. Age group had no effect on TEF, RQ or circulating glucose other than to delay the time of peak TEF (P<0.002 for both meals). There was no significant effect of meal type on TEF, but RQ and circulating glucose were higher following consumption of the palatable meal (P<0.001 for both parameters). These results suggest that over 6 h postprandial, consumption of palatable foods does not increase TEF, but is instead associated with increased glycemic response and increased carbohydrate oxidation. These changes, combined with previous work on the glycemic index, predict an accelerated return of hunger and increased energy intake at subsequent meals following consumption of palatable vs. control foods. Further studies are needed to examine the possible mechanism for this previously suggested "second meal" effect of diet palatability on energy intake.