Metabolic state and energy reserves jointly regulate adaptive behavioural control

Abstract

Animals continuously adapt their behaviour to changing physiological needs through flexible regulation of behavioural control. However, how the energetic state shapes the distinct components of this adaptive control in humans remains poorly understood. Here, we tested how fasting-induced energy deficits and stored energy reserves jointly regulate inhibitory control and incentive motivation in healthy participants. Fasting selectively increased impulsivity for food rewards, an effect attenuated by body fat percentage. In contrast, fasting increased effort expenditure across both food and monetary rewards, revealing a domain-general increase in motivation best explained by relative energy deficit--the ratio of energy expended during fasting to stored energy reserves. Neither effect was explained by changes in subjective reward valuation. Although self-report questionnaires captured stable behavioural tendencies, they failed to account for state-dependent behavioural variation. Together, these findings show that inhibitory control and motivation are governed by distinct metabolic principles operating across different timescales, revealing that adaptive behavioural control depends on the energetic significance of metabolic state rather than on fasting alone.