Metabolic state and energy reserve dynamically shape human decision-making

Behaviour is adaptive: To survive, organisms must continuously adjust their actions to their physiological needs. Yet, core behavioural dimensions such as impulse control and motivation are often treated as enduring traits, overlooking their dynamical regulation by physiological states. Here, we investigated how short-term energy deficits induced by fasting interact with longer-term energy reserves to shape human behavioural control. In healthy participants, fasting increased impulsivity selectively for food rewards, an effect attenuated by body fat percentage. Fasting also robustly increased effort expenditure across reward domains, indicating a domain-general motivational effect best predicted by relative energy deficit. Neither effect was explained by changes in subjective valuation. While self-report questionnaires of motivational, impulsivity, and eating-related traits captured stable behavioural tendencies and their association with body composition, they failed to account for state-dependent fluctuations. Together, these findings demonstrate that impulse control and motivation are flexibly regulated by the interaction of transient with sustained energy states, challenging trait-based accounts of human decision-making and highlighting its adaptive, state-dependent nature.