Patients with melanoma who consume a high-fiber diet during treatment with immune checkpoint inhibitors (ICIs) or anti-PD-1 therapy experience longer progression-free survival than those who don’t, researchers reported in Science. And probiotic supplementation, often considered a healthy behavior, reduces immunotherapy response.

Researchers analyzed the reported fiber and probiotics intake from 128 patients with advanced melanoma and compared it to their response to ICIs; they ran a simultaneous study in mouse models using anti-PD-1. They found that patients consuming at least 20 grams of fiber daily had longer progression-free survival than those consuming less and for every 5 gram increase in daily fiber intake, patients’ progression risk lowered by 30%.

In contrast, they found that patients or mice who used probiotics had lower levels of immune cells, less immunotherapy response, and larger tumors. The highest benefit across both studies occurred in patients who had high-fiber diets and did not use probiotics.

The researchers theorized that the response may be linked to proliferation of certain types of bacteria, such as Ruminococcaceae, that fiber encourages. Ruminococcaceae produces short-chain fatty acids that are associated with antitumor activity.

Additional studies are needed to confirm the findings. “Many factors can affect the ability of a patient with melanoma to respond to immunotherapy,” the researchers said. “However, from these data, the microbiota seems to be one of the dominant factors. The data also suggest that it’s probably better for people with cancer receiving immunotherapy not to use commercially available probiotics.”

Oncology nurses must educate patients about the importance of a healthy diet during treatment and into survivorship. Get tools for those conversations in ONS’s Nutrition Learning Library.