High protein diets do not attenuate decrements in testosterone and IGF-I during energy deficit.
Level 2 - randomized trial
Individual randomized controlled trial
PubMed 24641883 · doi:10.1016/j.metabol.2014.02.007
What was done
Thirty-three adults were assigned to diets providing protein at 0.8 (RDA), 1.6 (2x-RDA), or 2.4 (3x-RDA) g/kg/day for 31 days. Total and free testosterone, sex-hormone binding globulin (SHBG), and IGF-I system components were measured after a 10-day weight-maintenance phase and after a 21-day 40% energy deficit induced by increased energy expenditure and reduced intake. Associations between fat-free mass changes and hormone levels were analyzed.
What was found
Compared to weight-maintenance and across all protein intake groups, total and free testosterone, total IGF-I, and acid-labile subunit decreased (P < 0.05) during energy deficit, whereas SHBG and IGF binding proteins-1, -2, and -3 increased (P < 0.05). No energy-by-protein interactions were found for any hormone or IGF-I component. Changes in fat-free mass were negatively associated with acid-labile subunit only in the 2x-RDA group (r = -0.62, P < 0.05), with no other hormone-FFM relationships reported. Specific numeric hormone levels were not provided in the abstract.
Why it matters
These findings suggest that the muscle-sparing benefits of higher protein diets during calorie restriction occur independently of circulating testosterone and IGF-I preservation.
Limits
Small sample size (33 participants across three arms). The abstract does not disclose baseline characteristics, sex-specific differences, or absolute hormone concentrations, and the energy deficit period was limited to 21 days.
Cited by
- supports Severe caloric restriction causes testosterone levels, libido, and fertility to plummet in both men and women.