Ability to predict irregular periods of food deprivation improves body-weight regulation and reduces weight gain in food-insecure starlings

1.Food insecurity is associated with higher body weight in humans and other species, but the causal effect of unpredictable food availability on weight gain is unknown. We measured food intake and weight in starlings (Sturnus vulgaris) exposed to repeated irregular periods of food deprivation. We manipulated the predictability of deprivation between subjects with a 1-hour visual cue that either reliably preceded deprivation (Predictable), or was uncorrelated with deprivation (Unpredictable). During the cue, Predictable birds reduced their food intake and spent less time inactive, indicating that they had learnt the contingency. Despite these responses, they lost less weight during subsequent deprivation. They also ate less and gained less weight when food was returned. Birds with the largest behavioural response to the cue had the lowest overall variance in body weight. Consistent with the insurance hypothesis, food intake and body weight increased over time in both groups and body weight was higher in the Unpredictable group. Our results suggest that when food deprivation was predictable, birds were less reliant on stored fat and instead used conditioned hypometabolism to mitigate the effects of food deprivation. We discuss the implications of our findings for the differential health impacts of food insecurity and intermittent fasting.