I don't think it's something intrinsic to the diet. When you drop overall calories too low, the body senses starvation and looks for body functions it can cut back on to make sure other functions considered more necessary receive what energy there is coming in. So if you drop calories too low, you can expect your testosterone levels to drop and in turn your performance in the bedroom or your ability to even get it up. If you're having that problem then you need to gradually increase your daily calories regardless of which Keto expert you read said to take in X amount of calories because androgens play an important role in keeping what you burn while dieting geared towards fat rather than muscle.