It is known. Carbohydrate restriction improves (lowers) testosterone in women with PCOS. It works for men, too… but by “works” I mean “increases.”
Decrease of serum total and free testosterone during a low-fat high fibre diet (Hamalainen et al., 1982)
Intervention pseudo-crossover study: 30 healthy Finnish men in their 40’s were studied on their habitual high fat diet (40% fat), then put on a low-fat (25%) high fibre diet for 6 weeks, then switched back to high fat. The high fat diet was also higher in saturates, P:S ratio 0.15 vs. 1.25.
Free testosterone levels declined on the low fat diet, but they recovered after 6 weeks of going back to their high [saturated] fat dieting (p < 0.01).
Some observational data: Testosterone and cortisol in relationship to dietary nutrients and resistance exercise (Volek et al., 1997)
…fat, and in particular saturated fat, is associated with increased testosterone levels [in men]: