In March 2022, I published a meta-analysis that found ‘high-protein diets’ (>3.4 g/kg of bodyweight/day) (g/kg/day) decreased men’s testosterone . This finding was widely reported in the media, however the term ‘high protein diet’ was often used without qualification and context.
The diets in the meta-analysis classified as ‘high protein’ were >3.4 g/kg/day. This is an extreme amount of protein, and is more accurately described as a very high protein diet. For a 70kg individual, this is ~1.2kg lean meat per day. To put this into context, “the average protein intake is ∼1.3 g/kg/day, conventional ‘high-protein’ diets are ∼1.8–3 g/kg/day and the vast majority of athletes are <3.4 g/kg/day; meaning very few individuals will ever surpass 3.4 g/kg/day” .
Furthermore, protein intake is regulated by a protein specific appetite mechanism, which decreases your appetite for protein-rich foods when you have reached sufficiency (~1.9g/kg/day) . So you really have to pushing the boundaries and making a concerted effort to reach >3.4 g/kg/day.
The finding that very-high protein diets (>3.4g/kg/day) decreased testosterone was based on three studies with a total sample size of 26: thus the small sample size diminishes the quality of evidence. Also, the longest of these studies was 10 days: meaning it is unclear whether the decreased testosterone persists long-term.
The literature shows conventional high protein diets (1.9-3.4g/kg/day) have numerous benefits “including increased satiety, weight loss and greater preservation of lean mass during caloric deficits” [2,3]. They are healthy for the majority of people (besides those with kidney issues), and people should not to be dissuaded from adopting a high-protein diet (1.9-3.4g/kg/day) on the basis of this meta-analysis. However, there is little benefit to a very high protein diet (>3.4g/kg/day) and the safety of protein intakes >3.4g/kg/day is currently unclear .
For more information on this issue, please see the commentary article I have written – High-protein diets and testosterone.
- Whittaker J, Harris M (2022) Low-carbohydrate diets and men’s cortisol and testosterone: Systematic review and meta-analysis. Nutrition and Health, Online ahead of print. https://doi.org/10.1177/02601060221083079
- Whittaker J (2022) High-protein diets and testosterone. Nutrition and Health, Online ahead of print. https://doi.org/10.1177/02601060221132922
- Leidy HJ, et al. (2015) The role of protein in weight loss and maintenance. The American Journal of Clinical Nutrition 101(6):1320S-1329S. https://doi.org/10.3945/ajcn.114.084038