A balanced intake of different classes of nutrients is a key determinant of health, wellbeing, and aging. To ensure nutrient homeostasis animals adapt their foraging strategies according to their current and future needs. We want to understand how animals decide what to eat, how these decisions are shaped by brain-body interactions, and how these decisions affect the fitness of the animal. To achieve a mechanistic, integrated, whole-animal understanding of nutritional decision-making we work at the interface of behavior, metabolism, microbiome, and physiology in the adult Drosophila melanogaster. I will discuss how the powerful combination of activity imaging approaches, neurogenetics, connectomics, automated, quantitative behavioral analyses, and nutritional and microbial manipulations is allowing us to achieve a mechanistic understanding of how internal states shape neuronal circuits to optimize complex foraging decisions.