Abstract
<title>Abstract</title> <p> Background Alterations in food intake have been reported during spaceflight and may be influenced by exercise countermeasures. We examined whether supine aerobic cycling, with/without artificial gravity (AG), modified energy intake, food choices, and food reward during 60 days of head-down bed rest (HDBR). Methods Twenty-four healthy men (29.5 ± 5.7 years; BMI: 23.8 ± 1.8 kg/m <sup>2</sup> ) underwent 60 days of HDBR and were allocated to control (CNT), cycling (EX), or cycling plus AG (EX + AG). EI and food choices were assessed during an <italic>ad libitum</italic> multi-choice buffet, and food reward was assessed using the Leeds Food Preference Questionnaire before and after HDBR. Linear mixed-effects models tested time-by-group interactions as the primary effects and overall time effects across groups. Results No statistically significant time-by-group interactions were detected for any of the outcomes (all: <italic>p</italic> ≥ 0.10). Across groups, EI from the buffet decreased by 264 kcal (LSmean; 95%CI: -476 to -52; <italic>p</italic> = 0.017), whereas meal energy density increased (+ 0.34 kcal/g; 95%CI: 0.18 to 0.49; <italic>p</italic> < 0.001). Compositional analysis showed reduced protein intake relative to carbohydrate and fat (estimate: -0.117; 95%CI: -0.201 to -0.033; <italic>p</italic> = 0.007). <italic>Explicit liking</italic> bias decreased for high-protein (-6.2 a.u.; 95%CI: -11.1 to -1.4]; <italic>p</italic> = 0.015) and foods with color (-7.2 a.u.; 95%CI: -14.1 to -0.3; <italic>p</italic> = 0.043). <italic>Implicit wanting</italic> bias for high-fiber foods decreased (-13.4 a.u.; 95%CI: -22.6 to -4.1; <italic>p</italic> = 0.007). Conclusion Across groups, prolonged HDBR was associated with lower spontaneous EI, reduced relative contribution of protein to buffet intake, and selective changes in food reward. Neither EX nor EX + AG modified these responses, although the small group sizes limit firm conclusions regarding countermeasure effects. </p>