Some studies find that a high protein intake lowers testosterone levels….There is a positive association was seen with total fat and saturated fat, while a negative association was seen with protein and polyunsaturated fat. However, studies such as this one only look at total testosterone levels. When free testosterone is considered, a somewhat different picture emerges.
For instance: Testosterone concentrations in seven normal men were consistently higher after ten days on a high carbohydrate diet (468 +/- 34 ng/dl, mean +/- S.E.) than during a high protein diet (371 +/- 23 ng/dl, p less than 0.05) and were accompanied by parallel changes in sex hormone binding globulin (32.5 +/- 2.8 nmol/l vs. 23.4 +/- 1.6 nmol/l respectively, p less than 0.01). By contrast, cortisol concentrations were consistently lower during the high carbohydrate diet than during the high protein diet (7.74 +/- 0.71 micrograms/dl vs. 10.6 +/- 0.4 micrograms/dl respectively, p less than 0.05).

So the high carbohydrate diet raised total testosterone levels and lowered cortisol levels. These are both beneficial effects. However, the raising of SHBG is problematic.

So a high protein intake lowers total testosterone levels and raises cortisol levels. These are both detrimental effects. However, protein lowers SHBG and increases GH secretion. These are both beneficial effects. Given these conflicting effects of protein on hormone optimization, the best recommendation is to keep protein intake at a moderate level.

(Taylor, Joshua. Nutrition For A Higher Quality of Life. Testosterone Training 2009.)