The idea of hitting cancer cells where they are vulnerable is the basis of conventional cancer treatments such as radiotherapy or chemotherapy, which target the DNA of malignant cells. But the researchers also 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 therapy.
Many types of cancer cells depend on the amino acid methionine for their viability and growth. By limiting methionine intake, either through dietary changes or pharmaceutical intervention, or both, recent research offers hope that it may be possible to starve cancer cells, slow their growth or even stop it altogether.
Methionine is a sulfur amino acid that is a building block of protein in the body. It is essential, that is, the body cannot synthesize it on its own and must be consumed through food. According to the National Cancer Institute (NCI), besides 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 foods contain much more of it than most plant-based foods. According to MyFoodData.com, using data from USDA Food Data Central, eggs, fish, chicken, and turkey are among the foods highest in methionine, followed by beef, pork, and other meat products. of animal origin such as milk and cheese.
Even though methionine plays several important roles in the body, some people may benefit from a diet low in methionine.
NCI research over the past few decades has revealed an important fact about methionine: cancer cells have an abnormally high appetite for it and depend on this particular amino acid for growth. In experiments performed on mice, researchers found that feeding mice a methionine-restricted diet resulted in a decrease in the amount of methionine available to cells after just two days. Methionine-restricted mice also experienced slower growth of their cancerous tumors.
The researchers then tested to determine the effect of combining a methionine-restricted diet with chemotherapy or radiation treatments. They found that the combination of dietary changes and conventional treatments slowed tumor growth or shrunk tumors much more than conventional treatments alone.
Another study, published in the May 2019 issue of the journal Cells, demonstrated that administration of a laboratory-developed methionine restriction enzyme, recombinant methionine, was highly effective in inhibiting tumor growth in the mouse.
While human studies are sparse, a small study in six healthy adults who followed a low-methionine diet for three weeks showed effects on cellular metabolism similar to those seen in mice, with significantly lower levels of methionine available to cells after a short time. time. These studies and many other related studies offer hope that methionine restriction, either through diet alone or in conjunction with a pharmaceutical methionine inhibitor, could lead to positive results in the treatment of cancer.
Interestingly, several other mouse studies also show that restricting methionine intake may provide additional benefits, including slower cell aging, better health, and even longer lifespan.
The recommended daily allowance (RDA) of methionine, described 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 reveals that most people eat much more than that. Looking at different subgroups or consumers, ranging from high-protein eaters to vegans, the study found that almost everyone eats above the RDA, with the average balanced diet containing almost four times the RDA . Even vegans ate more than double the RDA.
Mark Simon, director of the Nutritional Oncology Research Institute, points out that the optimal protein requirements for humans are actually significantly lower than what is normally provided by the standard American diet.
“The actual daily protein requirement is between 10 and 15 grams for an average adult. Excess protein is toxic and leads to elevated ammonia and uric acid. In addition, excess protein and especially animal protein disrupts the intestinal microbiome favoring pathogenic bacteria. A diet low in methionine is sustainable and favorable to health, [and] significantly slows down aging.
The majority of research exploring the benefits of a methionine-restricted diet has been done on mice, and it’s unclear how easily the results translate to humans. One of the major barriers to conducting low-methionine studies in humans is the difficulty of getting participants to follow a largely vegan diet for an extended period of time.
Yet knowing that most cancer cells require an excessive intake of methionine to grow presents a potential Achilles heel, and as research into nutritional therapies for cancer treatments continues, this will be a very hot field. promising.
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