Energy deficit is common during prolonged periods of strenuous physical activity and limited sleep, but the extent to which appetite suppression contributes is unclear. The aim of this randomized crossover study was to determine the effects of energy balance on appetite and physiologic mediators of appetite during a 72-hr period of high physical activity energy expenditure (PAEE, ˜2300kcal/d) and limited sleep designed to simulate military operations (SUSOPS). Ten men consumed an

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... diet while sedentary for 1d (REST) followed by energy balanced (BAL) and energy deficient (DEF) controlled diets during SUSOPS. Appetite ratings, gastric emptying time (GET), and appetite-mediating hormone concentrations were measured. Energy balance was positive during BAL (18±20%) and negative during DEF (-43±9%). Relative to REST, hunger, desire to eat and prospective consumption ratings were all higher during DEF (26±40%, 56±71%, 28±34%, respectively), and lower during BAL (-55±25%, -52±27%, -54±21%, respectively; Pcondition<0.05). Fullness ratings did not differ from REST during DEF, but were 65±61% higher during BAL (Pcondition<0.05). Regression analyses predicted hunger and prospective consumption would be reduced and fullness increased if energy balance were maintained during SUSOPS, and energy deficits of ≥25% would be required to elicit increases in appetite. Between-condition differences in GET and appetite-mediating hormones identified slowed gastric emptying, increased anorexigenic hormone concentrations, and decreased fasting acylated ghrelin concentrations as potential mechanisms of appetite suppression. Findings suggest that physiologic responses that suppress appetite may deter energy balance from being achieved during prolonged periods of strenuous activity and limited sleep.