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In this pre-registered study, we aimed to explore the protein leverage hypothesis in a general population by studying the relationship between habitual dietary protein intake, total energy intake, and body mass index (BMI), and whether proportion of ultra-processed food (UPF) was associated with any of these variables. We used regression-based analyses to investigate these phenomena in cross-sectional data from a Norwegian population-based study, the seventh survey of the Tromsø Study 2015-2016, (n = 11,152; 40-99 years). Total energy intake was negatively associated with proportion of dietary protein (L = -0.36, p < .001) and positively associated with dietary fat (L = 0.33, p < .001). Although we planned to test the relationship between BMI and dietary protein, there was no positive association between total energy intake and BMI meaning that these data were not suitable for testing an effect of protein leverage on BMI. Proportion of UPFs was positively associated with total energy intake (b = 554, p < .001), negatively associated with proportion of dietary protein (b = -2.0, p < .001), and positively associated with BMI (b = 0.011, p = .026). In summary, our study of middle-to-older aged Norwegians provides strong support for a protein leverage effect on energy intake.
Eriksen et al. (2026) studied this question.