Some time ago, I had a talk with one of my colleagues at the University. She was a sophisticated biologist who was commenting on the deficient nutritional status of students. She told me she could see the Vitamin A deficiencies in our students from their enlarged pupils, their myopia, their tall stature, and their poor skin. Many students used retinoic acid, under prescription, to battle acne and other skin issues but this did not address their deficient Vitamin A status. A high protein (and carb) diet induces Vitamin A deficiency. A low fat diet does so as well, she said.
When I looked into it more I found that Vitamin A is essential to the production of testosterone as well. Moreover, the high protein diets of body builders depleted their Vitamin A. And their low fat diets put them further into deficit.
I began taking a teaspoon of cod liver oil daily. My testosterone shot up.