You're not craving sugar, you're hunting protein
A theory borrowed from ecology, not nutrition, explains why a bag of chips never quite feels finished.
Ecologists Stephen Simpson and David Raubenheimer noticed something odd studying insects, then found it across dozens of species: animals regulate protein intake far more tightly than fat or carbohydrate intake. Push protein down in the diet and an animal doesn't eat less — it eats more of everything else, chasing the protein target it still needs.
Applied to humans, they call this protein leverage. Most modern diets run around 15 percent protein by calories. When ultra-processed foods dilute that further with cheap fat and refined carbohydrate, the theory predicts people will keep eating past fullness because their protein appetite hasn't been satisfied yet, even as their stomach fills with everything around it.
A 2017 analysis of US dietary survey data found exactly this pattern: as ultra-processed food made up a larger share of people's diets, protein's share fell and total calories climbed, while absolute protein intake barely moved.
It reframes overeating as a body running an old, sensible instinct — find the protein — against a food supply that quietly stopped supplying it.