Project Summary It is often assumed that animals rapidly adapt behaviorally and physiologically to nutritional challenges and that adaptations to such challenges carry implications for human health. Very little work has been conducted to directly test this assumption and our preliminary data indicate that dietary protein restriction exerts effects on protein motivation that continue once protein intake is normalized. The proposed project will assess the persistence of the effects of dietary protein restriction on two measures of protein motivation – preference and economic “demand” – and on the physiological correlates of protein motivation – FGF21 production and mesolimbic dopamine system activity in response to protein ingestion. The work proposed in this application will be the first to address the question of how animals adapt behaviorally and physiologically when dietary protein is normalized following a period of dietary protein restriction. This work will be significant because it will directly test the assumption, implicit in most work in the field, that animals dynamically respond to nutritional needs.