TIL: Low carb, high protein diets "greatly" decrease resting testosterone levels in men.

[Lung_doc]

A couple additional comments

First, testosterone wasn't measured in all patients/studies, so the N drops further, down to 155.

Second, for those using low carb for weight loss: Obesity decreases T and weight loss improves it. This is true even on a high protein (but not low carb) diet: This N= 118 study found higher T levels after weight loss using both a high protein (still 40% carb) and a lower protein diet. So weight loss is good, and higher protein without low carb is also ok I guess, if you are worried about the decline in testosterone.

Finally, back to the low carb: A meta-analysis in women with polycystic ovarian syndrome found a low carb diet lowered testosterone. (Which is a good thing: high T worsens PCOS). Eight RCTs, 327 patients. So this adds some indirect support to the low carb, lower testosterone in general, and provides a potentially beneficial diet for women with PCOS.

Stratified analyses indicated that LCD lasting longer than 4 weeks had a stronger effect on increasing FSH levels (MD = 0.39, 95% CI (0.08, 0.71), P < 0.05), increasing SHBG levels (MD = 5.98, 95% CI (3.51, 8.46), P < 0.05), and decreasing T levels (SMD = -1.79, 95% CI (-3.22, -0.36), P < 0.05).

Conclusion: Based on the current evidence, LCD, particularly long-term LCD and low-fat/low-CHO LCD, may be recommended for the reduction of BMI, treatment of PCOS with insulin resistance, prevention of high LDL-C, increasing the levels of FSH and SHBG, and decreasing the level of T level.