Low-carbohydrate diets and men's cortisol and testosterone: Systematic review and meta-analysis.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of dietary intervention trials
PubMed 35254136 · doi:10.1177/02601060221083079
What was done
A systematic review and random-effects meta-analysis (PROSPERO CRD42021255957) searched eight databases through May 2021 to examine the effects of low-carbohydrate (≤35% carbohydrate) versus high-carbohydrate diets on testosterone and cortisol in healthy adult men. Cochrane's risk of bias tool was used for quality assessment. Subgroup analyses were conducted for diet duration (<3 weeks vs. ≥3 weeks), protein intake (<35% vs. ≥35%), and exercise duration.
What was found
Twenty-seven studies with 309 total participants were analyzed: - Short-term (<3 weeks) low-carbohydrate diets increased resting cortisol (SMD 0.41, 95% CI [0.16, 0.66], p < 0.01), whereas long-term (≥3 weeks) diets had no consistent effect on resting cortisol. - Following long-duration exercise (≥20 min), low-carbohydrate diets elevated post-exercise cortisol at 0 h (SMD 0.78 [0.47, 1.1], p < 0.01), 1 h (SMD 0.81 [0.31, 1.31], p < 0.01), and 2 h (SMD 0.82 [0.33, 1.3], p < 0.01). - Moderate-protein (<35%) low-carbohydrate diets had no consistent effect on resting total testosterone. - High-protein (≥35%) low-carbohydrate diets substantially decreased resting total testosterone (SMD -1.08 [-1.67, -0.48], p < 0.01; ~5.23 nmol/L) and post-exercise total testosterone (SMD -1.01 [-2.00, -0.01], p = 0.05).
Why it matters
The findings demonstrate that resting cortisol elevations from low-carbohydrate intake are transient while exercise-induced cortisol increases persist, and that reductions in testosterone are driven by high protein intake rather than carbohydrate restriction alone.
Limits
The total sample size across 27 studies was small (309 participants, averaging ~11 participants per study). The review was restricted to healthy adult males, and the abstract does not report data on free testosterone, blinding, adherence, or clinical health endpoints.
Cited by
- context Switching from a standard macronutrient diet containing starches to a low-carbohydrate diet significantly increases cortisol levels.