Associations of dietary proteins with serum total testosterone and sex hormone-binding globulin concentrations in middle-aged men.

Evidence linking dietary protein intake with testosterone and sex hormone-binding globulin (SHBG) is limited. We examined these associations in 2,546 Finnish men aged 42-60 years using 4-day food records and multivariable-adjusted models. Higher total and animal protein intakes and a higher animal-to-plant protein ratio were associated with lower total testosterone and SHBG, whereas plant protein intake was positively associated with both. In the highest versus lowest animal protein quartile, total testosterone was 1.2 nmol/L lower (95% CI: 0.37-2.03) and SHBG 3.0 nmol/L lower (95% CI: 1.34-4.66). In the highest versus lowest plant protein quartile, total testosterone was 1.1 nmol/L higher (95% CI: 0.34, 1.93) and SHBG 3.0 nmol/L higher (95% CI: 1.06, 4.94). Free testosterone was inversely associated with the animal-to-plant protein ratio and positively with non-grain plant protein. These cross-sectional findings suggest opposite associations of animal and plant protein intakes with total testosterone and SHBG.