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Impact of Exercise in the Fasted State on Prospective Food Consumption

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Abstract

INTRODUCTION: Exercise is recommended for weight management, yet weight loss from exercise is often less than expected based on measured energy expenditure. This is primarily due to compensatory energy intake, which occurs in most exercisers and overrides the appetite-suppressing effects of acute exercise. Exercising in a fasted state seems to be a promising way to decrease overall energy intake, as it has been reported that ad libitum 24h energy intake following fasting exercise is significantly lower than after non-fasting exercise. Acute effects of fasted exercise on post-exercise energy intake and particularly on post-exercise decision-making about food remain poorly understood. Therefore, the present study aimed to investigate whether fasting exercise and exercise after a standardized breakfast have different effects on hypothetical post-exercise food intake. METHODS: In this crossover study, ten healthy participants (29.7 [SD=2.2] years, 22.8 [SD=2.1] kg/m2, 50% women, regular habitual exercise, regular breakfast consumption) completed two identical 30-min exercise sessions on either a treadmill or bike ergometer (as preferred). The exercise sessions occurred following (1) an overnight (12h) fast (FE) or (2) a standardized breakfast (BE; oatmeal, low-fat milk, and apple; ~10-15% of individual daily energy requirements) after an overnight fast. Before (pre), immediately after (post), and 30 minutes after (post30) the exercise session, participants completed electronic questionnaires with visual food cues to determine hypothetical food amount preferences and intertemporal food preferences (immediate vs. delayed consumption after 4 hours). RESULTS: The preferred food amount for immediate consumption was significantly decreased compared to pre immediately after FE (161 [SD=85] kcal vs 236 [SD=81] kcal, p=0.006) but not after BE (p=0.26). For both exercise conditions, the amount of food selected for immediate consumption at post30 was significantly greater compared to pre (FE: 309 [SD=93] vs 236 [SD=81], p<0.001; BE: 201 [SD=103] vs 124 [SD=67], p=0.009). The preferred food amount for immediate consumption was significantly greater for FE compared to the BE, both for pre (difference: 113 [SD=57] kcal, p<0.001) and post30 (difference: 109 [SD=87] kcal, p=0.004) but not post (p=0.47). There were no significant differences between time points for delayed consumption in either exercise condition. CONCLUSION: The results of the present study suggest that fasting exercise may contribute to an overall daily energy deficit despite higher post-exercise energy intake (at post30) compared to exercise after a small breakfast. Importantly, hypothetical food intake did not differ between the two conditions immediately after exercise, suggesting that consumption of a meal at that time might maximize the calorie deficit-related benefits of fasting exercise. More (longitudinal) research in larger samples is needed to determine whether fasting exercise is an adequate method for weight loss.

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Stress, and Nausea did not differ between Fasting and Breakfast at any time point (all P≥0.06)
  • Thirst Fullness
Fullness, Thirst, Stress, and Nausea did not differ between Fasting and Breakfast at any time point (all P≥0.06)