The old cliche "You are what you eat" contains a fair amount of truth. A man's body, including his sex organs, is made from the food he eats, the beverages he drinks, and the air he breaths. Eat right, and everything improves--including sexual health. As with most things in life an appropriate guide for eating to promote sexual health is: "All things in moderation, including excess." The idea is to avoid extremes in any direction and yet to preserve the pleasure of eating as well.
For example, much research shows that a high-fat diet and obesity lower testosterone levels and increase the risk of erection problems. That's because excess fat gets converted to estrogen-like compounds which curtail the production of testosterone, and fat in the blood can clog the small arteries feeding the penis. What is bad for the heart is bad for the penis.
On the other hand, studies also show that very lean men--for example marathon runners--also have lower-than-average testosterone levels. That's because the compound used to build testosterone molecules in the body is cholesterol, and extreme exercise lowers cholesterol levels to abnormal levels. A man needs enough cholesterol in his diet to maintain testosterone production, but not so much that it produces body fat or clogged arteries.