Investigation into gender differences in the effects of feeding around exercise on energy expenditure and substrate utilization

Abstract

Nutritional advice to optimise athletic performance is often not applicable for the majority of people who exercise for health or weight maintenance. A common perception by laypersons is that exercising on an empty stomach (fasted) increases fat oxidation, hence aids fat loss (1) . However research on feeding around exercise mainly focuses on performance in trained or semi-trained individuals (2) . Furthermore, research is most commonly undertaken on males, despite accepted gender difference in substrate metabolism and energy expenditure (EE) (3) . This study aimed to investigate the impact of CHO consumption before and after treadmill exercise on substrate utilization and total EE in untrained men and women.Fifteen healthy, untrained subjects (7 male, 8 female) aged 21-33 years undertook a randomised crossover study. Subjects completed 2 treatments, separated by a washout period ( ‡ 3 days), following an overnight fast. At each treatment subjects exercised for £ 30 min on a treadmill at approximately 70 % VO2 max, with 30 g of maltodextrin or placebo ingested either before or after exercise. EE (kJ/min), and Fat and CHO utilization (g/hr) during and over 3 hours post exercise were estimated by indirect calorimetry. This study was approved by the University of Surrey Faculty of Health and Medical Sciences Ethics Committee.Fat oxidation rates between CHO and placebo were only significantly different during exercise for males (placebo > CHO), and during recovery for females (placebo > CHO). Over the whole study a significant difference in total fat oxidation (g) between the two feeding regimes was observed in females (P = 0.034) but not males (see Table 1). Males had a significantly greater difference in total fat oxidation (g) (P = 0.018) and % EE from fat oxidation (P = 0.037) compared with females between treatments. Significant gender differences in EE (kcal/d/kg) were observed during recovery following CHO intake only with males expended 160 kcal/d/kg more than females (P = 0.05).

The effect of food timing on fat oxidation during exercise and resting recovery

“…Our findings failed to show a significant effect of the timing of carbohydrate around exercise training on fat oxidation either at rest, during, or post-exercise, possibly attributable to a small sample size. However, trends observed supprt the findings of Fuchs and Young ( 2 ) suggesting that, in women, consuming carbohydrate before exercise may potentially be more beneficial for fat oxidation than consuming carbohydrate post-exercise. Larger placebo-controlled trials may have better potential to fully elucidate optimal eating strategies around exercise.…”