Mito
Member
- Joined
- Dec 10, 2016
- Messages
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Abstract
Background: Low-carbohydrate diets may have endocrine effects, although individual studies are conflicting. Therefore, a review was conducted on the effects of low- versus high-carbohydrate diets on men’s testosterone and cortisol. Methods: The review was registered on PROSPERO (CRD42021255957). The inclusion criteria were: intervention study, healthy adult males, and low-carbohydrate diet: ≤35% carbohydrate. Eight databases were searched from concep- tion to May 2021. Cochrane’s risk of bias tool was used for quality assessment. Random-effects, meta-analyses using stan- dardized mean differences and 95% confidence intervals, were performed with Review Manager. Subgroup analyses were conducted for diet duration, protein intake, and exercise duration. Results: Twenty-seven studies were included, with a total of 309 participants. Short-term (<3 weeks), low- versus high-carbohydrate diets moderately increased resting cor- tisol (0.41 [0.16, 0.66], p < 0.01). Whereas, long-term (≥3 weeks), low-carbohydrate diets had no consistent effect on resting cortisol. Low- versus high-carbohydrate diets resulted in much higher post-exercise cortisol, after long-duration exercise (≥20 min): 0 h (0.78 [0.47, 1.1], p < 0.01), 1 h (0.81 [0.31, 1.31], p < 0.01), and 2 h (0.82 [0.33, 1.3], p < 0.01). Moderate-protein (<35%), low-carbohydrate diets had no consistent effect on resting total testosterone, however high- protein (≥35%), low-carbohydrate diets greatly decreased resting (−1.08 [−1.67, −0.48], p < 0.01) and post-exercise total testosterone (−1.01 [−2, −0.01] p = 0.05). Conclusions: Resting and post-exercise cortisol increase during the first 3 weeks of a low-carbohydrate diet. Afterwards, resting cortisol appears to return to baseline, whilst post-exercise cortisol remains elevated. High-protein diets cause a large decrease in resting total testosterone (∼5.23 nmol/L).
Conclusions
This review found an increase in resting and post-exercise cortisol on short-term LC diets (<3 weeks). In addition, the results indicate resting cortisol levels return to baseline after ∼3 weeks on a LC diet, whilst post-exercise cortisol remains elevated. However, due to the low number of studies and unexplained heterogeneity in long-term LC diets, further research is needed to confirm the latter effects. MP-LC diets appear to have no effect on resting TT, although the decrease in resting TT on randomized MP-LC studies, highlights the need for further randomized controlled trials. Finally, HP-LC diets caused a large decrease in resting TT, suggesting individuals consuming such diets may need to be cautious about adverse endocrine effects.
Background: Low-carbohydrate diets may have endocrine effects, although individual studies are conflicting. Therefore, a review was conducted on the effects of low- versus high-carbohydrate diets on men’s testosterone and cortisol. Methods: The review was registered on PROSPERO (CRD42021255957). The inclusion criteria were: intervention study, healthy adult males, and low-carbohydrate diet: ≤35% carbohydrate. Eight databases were searched from concep- tion to May 2021. Cochrane’s risk of bias tool was used for quality assessment. Random-effects, meta-analyses using stan- dardized mean differences and 95% confidence intervals, were performed with Review Manager. Subgroup analyses were conducted for diet duration, protein intake, and exercise duration. Results: Twenty-seven studies were included, with a total of 309 participants. Short-term (<3 weeks), low- versus high-carbohydrate diets moderately increased resting cor- tisol (0.41 [0.16, 0.66], p < 0.01). Whereas, long-term (≥3 weeks), low-carbohydrate diets had no consistent effect on resting cortisol. Low- versus high-carbohydrate diets resulted in much higher post-exercise cortisol, after long-duration exercise (≥20 min): 0 h (0.78 [0.47, 1.1], p < 0.01), 1 h (0.81 [0.31, 1.31], p < 0.01), and 2 h (0.82 [0.33, 1.3], p < 0.01). Moderate-protein (<35%), low-carbohydrate diets had no consistent effect on resting total testosterone, however high- protein (≥35%), low-carbohydrate diets greatly decreased resting (−1.08 [−1.67, −0.48], p < 0.01) and post-exercise total testosterone (−1.01 [−2, −0.01] p = 0.05). Conclusions: Resting and post-exercise cortisol increase during the first 3 weeks of a low-carbohydrate diet. Afterwards, resting cortisol appears to return to baseline, whilst post-exercise cortisol remains elevated. High-protein diets cause a large decrease in resting total testosterone (∼5.23 nmol/L).
Conclusions
This review found an increase in resting and post-exercise cortisol on short-term LC diets (<3 weeks). In addition, the results indicate resting cortisol levels return to baseline after ∼3 weeks on a LC diet, whilst post-exercise cortisol remains elevated. However, due to the low number of studies and unexplained heterogeneity in long-term LC diets, further research is needed to confirm the latter effects. MP-LC diets appear to have no effect on resting TT, although the decrease in resting TT on randomized MP-LC studies, highlights the need for further randomized controlled trials. Finally, HP-LC diets caused a large decrease in resting TT, suggesting individuals consuming such diets may need to be cautious about adverse endocrine effects.
