their T-cell activity. The fiber-rich diet made no difference, however, in mice with no gut bacteria. According to Wargo, that suggests the diet exerted its effects via the gut microbiome.
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How safe are supplements?
After a cancer diagnosis, Wargo says, people often want to do something to take control and help support their treatment.
Sometimes they turn to supplements. But based on the current findings, Wargo says, caution may be in order.
“People undergoing cancer treatment should discuss probiotic use with their care team,” she suggests.
As for fiber, Mayer says more study is needed. He notes that there is “a lot of basic science” to support the notion that fiber could benefit cancer patients via the gut microbiome.
But to prove that, Mayer says, clinical trials will have to test the effects of adding fiber to patients’ diets. He notes that plant foods, the main source of dietary fiber, also have other nutrients, including polyphenols, that could be part of the story as well.
A trial putting fiber to the test is underway, according to Wargo. The researchers are enrolling melanoma patients receiving immunotherapy and will randomly assign them to varying amounts of dietary fiber, added to a healthy diet recommended by the American Cancer Society.
“It’s early days in this research,” Wargo shares. But ultimately, she adds, studies of diet, gut microbes and immune function could have broad implications — not only for people with various types of cancer, but everyone.
Could, for example, certain diets help people fight infections or respond better to vaccines, like those for the flu and COVID-19?
How to support a healthy gut microbiome
For anyone looking to support a healthy gut microbiome, Mayer says people should aim for a range of plant foods, as well as fermented foods like yogurt, fermented cottage cheese, kimchi and sauerkraut — which research has linked to greater diversity in gut bacteria.