Leucine is one of the three branched-chain amino acids, along with isoleucine and valine, and is considered an essential amino acid in humans. Essential amino acids are those you can obtain only through your diet. Leucine can be found in a variety of foods, including soy, nuts, oats, beans, lentils, corn and rice. Leucine is also available as a nutritional supplement. Ingesting too much leucine may cause some side effects. Talk with your doctor about leucine and the potential health risks of consuming too much.
According to Herbs2000.com, high amounts of leucine supplementation can cause ammonia to accumulate in your body. Too much ammonia circulating in your bloodstream may cause tissue damage and eventually organ failure. The liver and kidneys are especially susceptible to ammonia toxicity because they help the body filter out excess ammonia from the bloodstream. However, the amount of leucine required to cause ammonia toxicity is extremely high, making excessive ammonia buildup resulting from leucine supplementation unlikely.
Pellagra is a vitamin deficiency disease that typically results from a niacin deficiency, although high levels of leucine may also cause it to occur. Pellagra can make people highly sensitive to sunlight and can have many other detrimental effects. According to a 1978 study published in "The American Journal of Clinical Nutrition," excess leucine causes an amino acid imbalance in the body that can lead to the onset of pellagra. The researchers found that taking extra vitamin B-6 helps reduce leucine levels in the body and can counteract the symptoms of pellagra.
Leucine causes hypoglycemia, or low blood sugar levels, in some people, according to Drugs.com. Leucine can reduce blood glucose levels due to its ability to stimulate insulin production by the pancreas. Hypoglycemia can have a wide range of side effects, some of which are serious, according to PubMed Health. Talk to your doctor about leucine if you have diabetes or any other condition that affects your body's ability to produce insulin and regulate blood sugar.
According to the book "Anabolic Primer," high doses of leucine may cause gastrointestinal side effects. When ingested in dosages ranging between 2 and 5 g, leucine is generally considered safe and the potential for side effects is viewed as low. However, supplementation with upward of 15 g of leucine may cause effects such as upset stomach, nausea, diarrhea and vomiting.