Dietary protein density is inversely associated with energy intake in free-living adults

Abstract Dietary protein density has been proposed as a factor influencing energy intake through mechanisms described by the protein leverage hypothesis. We examined the association between dietary protein density, expressed as percentage of total energy intake from protein, and total daily energy intake in 179 free-living adults using seven-day food records. In multivariable linear regression adjusted for age and sex, each 1%-point higher protein contribution was associated with 52.1 kcal/day lower energy intake (95% CI − 84.9 to − 19.3; p = 0.002). A theory-driven power-function analysis yielded a leverage coefficient of L = − 0.456 (95% CI − 0.684 to − 0.229; p < 0.001), consistent with partial protein leverage. Secondary analyses provided modest evidence of non-linearity and possible age-related effect modification, whereas no significant effect modification by sex was observed. The inverse association remained evident in sensitivity analyses including adjustment for estimated basal metabolic rate and exclusion of potentially influential observations. These findings provide cross-sectional evidence consistent with the protein leverage framework under free-living conditions. However, the observational design and potential residual confounding preclude causal inference.