Overview
This trial's aim is to investigate the time-of-day effects (morning vs. evening) of fasted exercise on acute and 24h post-exercise energy intake. Specifically, we will compare the effects of fasted morning exercise (12h overnight fast) vs. fasted (6h and 12h) evening exercise on total energy intake during a post-exercise ad libitum test meal as well as on 24h (free-living) energy intake. The secondary aim is to assess subjective appetite ratings before, immediately after, and 30 min post-exercise (visual analog scale). Healthy men and women aged 18-30 years will be included.
Description
In a four-way crossover design, participants will complete three fasted and one non-fasted exercise sessions on a treadmill in randomized order on weekdays with one week in between sessions: once in the morning (~1h after participants' habitual wake-up time) following a 12h overnight fast (12h AMEx), once in the evening (exactly 12h after the 12h AMEx condition) after a 6h fast (6h PMEx), and once in the evening (identical to the 6h PMEx condition) following a 12h fast (12h PMEx). As a control condition, participants will also complete a morning exercise session in a fed state (i.e., after consuming a small pre-exercise snack 30 min before exercise; 12h AMEx-Fed). The last meal before each fasting period will be standardized, providing 25% (meal occurring 12h before exercise) and 30% (meal occurring 6h before exercise, 6h PMEx only) of individual daily energy requirements.
Eligibility
Inclusion Criteria:
- BMI of 18.5.0-30.0 kg/m2
- weight stability (≤2.5 kg weight change during the past 3 months)
- ability to exercise at a vigorous intensity for 30 minutes
Exclusion Criteria:
- pregnancy or breastfeeding
- smoking
- history of or current eating disorders
- medical condition or use of medication that could affect appetite or pose any contraindications to exercise
As the menstrual cycle can cause fluctuations in food cravings and appetite, women of childbearing age were only eligible if they used hormonal contraceptives. To ensure constant exposure to exogenous estrogen and progestin throughout the study phase, participating women were further asked to use active hormone pills throughout the study period in both studies, a practice that is considered both safe and efficacious.
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