The idea of hitting cancer cells where they’re vulnerable is the basis of conventional cancer treatments such as radiation or chemotherapy, which target the DNA of malignant cells. But researchers also have identified other, cancer-specific vulnerabilities.
Cancer cells have unique nutritional needs that differ from the healthy cells around them, and identifying these cancer-specific characteristics opens up potential areas for targeted treatment.
Many types of cancer cells are dependent on the amino acid methionine for their viability and growth. By restricting methionine intake, either through dietary changes, pharmaceutical intervention, or both, recent research offers hope that it may be possible to starve cancer cells, slowing their growth or even stopping it altogether.
Methionine is a sulfur-containing amino acid that is a building block of proteins in the body. It’s essential, meaning that the body can’t synthesize it on its own, and must be consumed through diet. According to the National Cancer Institute (NCI), aside from its role in protein synthesis, methionine is also directly or indirectly involved in many other important processes, including cellular metabolism and DNA repair. A certain amount of methionine is essential for human life.
Methionine is found in most protein-containing foods, but animal-derived foods contain much more than most plant-based foods. According to MyFoodData.com, using data from USDA Food Data Central, eggs, fish, chicken, and turkey are some of the highest methionine-containing foods, followed by beef, pork, and other animal products such as milk and cheese.
Even though methionine plays several important roles in the body, some people may benefit from a low-methionine diet.
NCI research in recent decades has uncovered an important fact about methionine—cancer cells have an abnormally large appetite for it and are dependent upon this particular amino acid for their growth. In experiments done on mice, researchers found that feeding mice a methionine-restricted diet resulted in lower amounts of methionine being available for use by cells after just two days. The methionine-restricted mice also experienced slowed growth of their cancerous tumors.
Researchers then tested to determine the effect of combining a methionine-restricted diet along with chemotherapy or radiation treatments. They found that the combination of dietary changes plus conventional treatments slowed tumor growth, or shrank the tumors, significantly more than the conventional treatments alone.
Another study, published in the May 2019 edition of the journal Cells, demonstrated that administering a lab-developed methionine-restricting enzyme, recombinant methioninase, was highly effective in inhibiting tumor growth in mice.
While studies on humans are sparse, one small study involving six healthy adults who ate a low-methionine diet for three weeks, showed effects on cell metabolism similar to that observed in the mice, with significantly lower levels of methionine available to cells after a short time. These and many other related studies offer hope that restricting methionine, either through diet alone or in conjunction with a pharmaceutical methionine inhibitor, could lead to positive outcomes in cancer treatment.
Interestingly, several other studies on mice also show that restricting methionine consumption could offer additional benefits including slower cellular aging, improved health, and even extended lifespan.
The recommended daily allowance (RDA) of methionine, outlined in the November 2007 issue of the journal Nutrition and Metabolism, is low—just 1.1 grams per day for a 154-pound (70-kg) person, although some experts recommend double that amount. However, the study finds most people are eating far more than that. Looking at different subgroups or eaters, ranging from high-protein eaters to vegans, the study found nearly everyone eats above the RDA, with an average balanced diet containing nearly four times the RDA. Even vegans ate more than double the RDA.
Mark Simon, director of the Nutritional Oncology Research Institute, stresses that optimal protein requirements for humans are actually significantly less than what is normally provided through the standard American diet.
“Actual daily protein requirement is between 10-15 grams for an average adult. Excess protein is toxic resulting in the elevation of ammonia and uric acid. In addition, excess protein and especially animal protein disturbs the gut microbiome favoring pathogenic bacteria. A low methionine diet is sustainable and health-promoting, [and] greatly slows aging.”
The majority of research exploring the benefits of a methionine-restricted diet has been done on mice, and it is unclear how easily the results translate to humans. One major obstacle to conducting low-methionine studies on humans is the difficulty of getting participants to actually follow a largely vegan diet for an extended period of time.
Still, knowing that most cancer cells require excessive methionine intake to grow presents a potential Achilles’ heel, and as research into nutritional therapies for cancer treatments continue, this will be an area that shows great promise.
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