In many men low testosterone is caused by reversible conditions, such as excess body fat and chronic disease (e.g., type-2-diabetes, metabolic-syndrome). Consequently, a hypocaloric diet is very effective for increasing testosterone levels in this population,[1] whereas a hypocaloric diet seems to reduce testosterone levels in lean men.[2][3]
In addition, it’s worth paying attention to dietary fat levels, because limited evidence suggests that low-fat diets (≤25% of energy intake) decrease testosterone levels compared to higher-fat diets (about 40% of energy intake).[4]