Acute effects of pre-exercise high and low glycaemic index meals and exercise timings on substrate metabolism and appetite in postmenopausal women.

backgroundPostmenopausal women are often reported to exhibit increased susceptibility to metabolic disorders. Although the consumption of low glycaemic index (LGI) foods before exercise are known to enhance fat oxidation during exercise, the optimal exercise timing has not been evaluated. We investigated the effects of pre-exercise meals with different GI values and exercise timings on substrate metabolism and appetite in postmenopausal women.

methodsFifteen postmenopausal women completed four trials in a random manner. Participants consumed energy-matched high GI (HGI) or LGI meal at 0900 and rested until 1000 (60 min-HGI and -LGI trials) or 1100 (120 min-HGI and -LGI trials). Then, participants performed a 30-min walk at 50% of estimated maximum oxygen uptake and rested until 1300. Expired air, blood samples, ratings of food reward and subjective appetite were collected.

resultsNo differences in fat oxidation during exercise were observed among trials (P = 0.66). The area under the curve of 3-hydroxybutyrate was higher in the 120 min-LGI trial compared to the 60 min-LGI trial (P = 0.01) after exercise. Relative preference for high-fat foods after exercise and subjective appetite during post-exercise for 1-hour were not different between the 60 min-LGI and 120 min-LGI trials.

conclusionsThese findings indicate that a different timing of pre-exercise LGI meal did not influence fat oxidation during exercise, post-exercise food reward or subjective appetite in postmenopausal women. However, a longer interval between meal consumption and subsequent exercise may be effective in enhancing post-exercise hepatic fatty acid oxidation.