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

We investigated the effects of food palatability on the thermic effect of f eeding (TEF), substrate oxidation and circulating glucose and insulin. Heal thy 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 perio ds. 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 con taining the same foods in identical amounts but blended and freeze-dried in to biscuit form. TEF and respiratory quotient (RQ) were measured over 6 h a nd blood samples were taken for measurement of glucose and insulin. Age gro up 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 effec t 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 r esults suggest that over 6 h postprandial, consumption of palatable foods d oes not increase TEF, but is instead associated with increased glycemic res ponse and increased carbohydrate oxidation. These changes, combined with pr evious work on the glycemic index, predict an accelerated return of hunger and increased energy intake at subsequent meals following consumption of pa latable vs. control foods. Further studies are needed to examine the possib le mechanism for this previously suggested "second meal" effect of diet pal atability on energy intake. (C) 2001 Elsevier Science Inc. All rights reser ved.