Evidence for a protein leverage effect on food intake but not on body mass index in a Norwegian population
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Objective
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.
Methods
We used regression-based analyses to investigate these phenomena in cross-sectional data from a Norwegian population-based study, the seventh survey of Tromsø Study 2015-2016, ( n = 11,152; 40-99 years).
Results
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). 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).
Conclusions
In 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 Questions
What is already known about this subject?
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The protein leverage hypothesis proposes that a strong appetite for protein plays a crucial role in the obesity epidemic.
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Though 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.
What are the new findings in your manuscript?
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In 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.
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In 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.
How might your results change the direction of research or the focus of clinical practice?
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Our results highlight the important association between dietary protein and energy intake and the potential contribution of ultra-processed foods to this relationship.
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We 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.
