Evidence for a protein leverage effect on food intake but not on body mass index in a Norwegian population

ObjectiveIn 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. MethodsWe used regression-based analyses to investigate these phenomena in cross-sectional data from a Norwegian population-based study, the seventh survey of Tromso Study 2015-2016, (n = 11,152; 40-99 years). ResultsTotal 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). The relationship between BMI and dietary protein was positive but small (b = 0.01, p < .001). 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). ConclusionsIn summary, our study of middle-to-older aged Norwegians provides strong support for a protein leverage effect on energy intake but no evidence for an effect of protein leverage on BMI. Study Importance QuestionsO_ST_ABSWhat is already known about this subject?C_ST_ABSO_LIThe protein leverage hypothesis proposes that a strong appetite for protein plays a crucial role in the obesity epidemic. C_LIO_LIThough dietary protein is strongly linked to energy intake, in the context of protein leverage, no studies have found the predicted relationship between protein intake and body mass index. C_LI What are the new findings in your manuscript?O_LIIn a population-based study, we find that dietary protein and energy intake are related - in line with an effect of protein leverage - but we find no relationship between protein and body mass index. C_LIO_LIIn our sample of women and men 40-99 years, a higher intake of ultra-processed foods is associated with higher energy intake and lower proportion of dietary protein, highlighting this class of foods as a possible dilutant of protein in the food supply. C_LI How might your results change the direction of research or the focus of clinical practice?O_LIOur results highlight the important association between dietary protein and energy intake and the potential contribution of ultra-processed foods to this relationship. C_LIO_LIWe suggest that further research should be devoted to understanding how the hormone FGF21 - which is increased by low protein diets - might interact both with appetite and energy expenditure to affect body mass index. C_LI