Eating a lot of fiber could improve some cancer treatments

ALWAYS GOOD ADVICE Eating more foods high in fiber has been recommended to prevent cancer. Now researchers say high-fiber diets may also help a type of immune therapy work better against tumors.
The same can’t be said for taking probiotics, researchers suggest

By Tina Hesman Saey | ScienceNews

What you eat can affect how well immune therapies work against cancer. High-fiber diets may change gut microbes and make these therapies more effective, but taking probiotics could do the opposite.

Researchers looked at people with melanoma skin cancer who were getting a kind of immune therapy called PD-1 blockade or checkpoint inhibition (SN: 10/27/18, p. 16). Those who ate a high-fiber diet were five times as likely to have the therapy halt the growth of or shrink tumors as those on diets low in fiber, researchers reported February 27 in a news conference held by the American Association for Cancer Research.

High-fiber diets seem to foster a more diverse collection of gut microbes, which is associated with better outcomes from PD-1 blockade therapy, said Christine Spencer, a research scientist at the Parker Institute for Cancer Immunotherapy in San Francisco. But probiotic supplements — pills or food supplements that are supposed to contain helpful bacteria — actually reduced the diversity of microbes in cancer patients’ guts, the researchers found.

Only about 20 to 30 percent of cancer patients see their tumors stop growing or shrink with PD-1 blockade immunotherapy. Spencer and colleagues had previously determined that bacteria in the Ruminococcaceae family seem to improve responses to the treatment, but the researchers didn’t know why some people have more of those helpful bacteria than others.

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