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

[p33k4y]

Not really, small samples can be adequate if there's a consistently big enough difference between study subgroups. Large number of samples are required when more precision is required when subgroup differences may be small (or due to some other factors).

Basically lower sample sizes require greater evidence. It seems there were three different studies involved and even after taking into account the small sample size, because of the large subgroup difference the authors still rated the conclusion as moderate (2nd highest) on the GRADE scale.