Research in mice suggests that an essential nutrient methionine supplement combined with radiation therapy impairs gut function to promote a life-threatening form of radiation toxicity. The study, published in the American Journal of Physiology—Gastrointestinal and Liver Physiology, highlights the importance of food and nutrition professionals as part of a cancer treatment team. 

Methionine is an essential amino acid important for building protein and, in turn, muscles. People get methionine through diet: eggs, dairy products, poultry, fish, pork and sesame seeds are high in the nutrient. Amino acid supplementation—under the supervision of a doctor or registered dietician—with a single amino acid or a combination amino acid supplement has played a role in treating a life-threatening form of muscle wasting that many people with advanced cancer experience. However, past studies in animals have shown that too much methionine can harm the gastrointestinal tract and that controlled restriction of methionine in the diet may be an effective part of cancer treatment.

Radiation therapy is a primary form of cancer treatment for millions of people with the disease. Damage to the digestive system caused by radiation—a condition called gastrointestinal radiation syndrome—affects as many as 2 million cancer survivors who have had radiation. Symptoms of this complication can be life-threatening and may include nausea and vomiting, diarrhea, loss of appetite, dehydration, electrolyte imbalance and the development of body-wide infection (sepsis). To date, there is no approved treatment from the US Food and Drug Administration to prevent or treat gastrointestinal radiation syndrome.

In a new study, researchers looked at the combined effects of methionine and radiation on gastrointestinal radiation syndrome in a mouse model. Mice received either one of three different doses of radiation or no radiation. After treatment, all animals were randomly divided into two new groups. One group ate a diet that provided normal levels of methionine. The other group was given a supplemented diet that delivered 300% of typical methionine levels, as some epidemiological studies indicate that consuming high amounts of dietary methionine is common in Western populations. The researchers found that dietary methionine supplementation resulted in development of gastrointestinal toxicity even at lower doses of radiation that previously had not been associated with radiation syndrome in mice. Alterations in gut microbiota and presence of bacterial DNA in the liver tissue suggest that the combined treatment impaired normal gut physiology, leading to gastrointestinal radiation syndrome.

“This study demonstrates that dietary methionine supplementation, instead of an anticipated health promoting effect, sensitizes mice to [gastrointestinal radiation syndrome],” the researchers wrote. “These findings also speak toward increasing the role of registered dietitians during cancer therapy and the necessity of solid scientific background behind the sales of dietary supplements and claims regarding their beneficial effects.”