A study sponsored by the Italian government and published in the International Journal of Endocrinology recently examined the link between sufferers of type-II diabetes and low testosterone levels.
The Italian researchers exposed gonadotropin-releasing hormone, a substance secreted by the hypothalamus that triggers insulin release, to high levels of glucose. The glucose blunted the amount of gonadotropin-releasing hormone that was secreted, thus limiting testosterone production. The level of glucose in the blood used in the test was roughly equal to what someone might experience if they binged on rapidly absorbed carbohydrates. If someone has poor insulin sensitivity and goes overboard on sugary carbs, they can easily reach the range of blood glucose that begins to inhibit testosterone production.