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Erectile dysfunction in varying degrees is not uncommon in bodybuilders who consume large amounts of protein in the hopes that it will help them gain muscle. The problems with impotence in this kind of situation are usually not overwhelming, but a man's, well, manhood may not be all that he would like it to be.

The underlying problem isn't protein. It's the way the body regulates uses one of the amino acids found in protein called methionine. The first thing to understand about methionine is that it is an "essential" amino acid. Humans and other animals can't make it. They have to get it from food. We can get it from meat or fish or dairy products, but the animal we get it from had to get it by eating another animal or a plant.

Methionine is constantly being created from and used to make other amino acids. It can be transformed into an anti-inflammatory compound called s-adenosylmethionine (SAMe), which can be transformed into homocysteine, which can be turned back into methionine as the body needs it. Converting homocysteine back into methionine requires enzymes that in turn require an activated form of folic acid called methylfolate and vitamin B12 to work. Alternatively, with the help of enzymes that require vitamin B6, homocysteine can be converted into another amino acid called cysteine.

Problems arise when something goes wrong with the conversion process and lots of homocysteine builds up. Homocysteine irritates blood vessles. Excess homocysteine keeps the linings of blood vessels from generating a compound called nitric oxide or NO, which lets them dilate. And dilation is the process that enables the penis to fill with blood and to become erect. 

If you get (1) too much methionine and (2) not enough of the right forms of folic acid, vitamin B12, and vitamin B6, then (3) the blood vessels in your penis may not generate enough NO for a full erection. There are actually many other serious consequences all over your body, an increased risk of heart attacks and reduced brain function, for example, although most men who are using protein supplements are primarily concerned about loss of erectile function.

What do you do if you have unsatisfactory erections while you are using protein supplements?

  • First of all, start taking a supplement called methylfolate. About 22 percent of men in Europe and North America have a hereditary problem that causes their bodies to fail to process the B vitamin folic acid into its active form. Taking supplemental B vitamins that contain the regular form of folic acid (or folate) actually makes the problem worse. You need methylfolate, not folic acid or folate or a "complete B vitamin." This can take care of part of the problem.
  • Then it also helps to take vitamin B6 and vitamin B12. You don't necessarily need to take a special form of those vitamins, although it won't hurt.
  • Next, consider whether you really need to be consuming large amounts of protein supplements. Your muscles don't just need the amino acids from protein to grow. They can respond to creatine. Creatine, by the way, is found in meat as well as in supplements. It combines with water to create bulk in muscles. You don't take a regular protein supplement to get protein. Your muscles use amino acids when they are stimulated by growth hormone. Your brain makes more growth hormone when you get regular rest, when you give your body a break from eating protein all the time (growth hormone protects you against ill effects of fasting by putting amino acids into your muscles), preferably about 18 hours twice a week without protein meals, and when you have a healthy sex life.

That's right. A healthy sex life helps your muscles grow. So if you're having problems with your sex life when you are taking protein supplements, pull back on the protein supplements for a couple of weeks and see what happens. Then make sure you are taking methylfolate (again, not folic acid), vitamin B6, and vitamin B12 as you restart your protein supplements again gradually.

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