Food can affect the effectiveness of immunotherapy against cancer, and a high-fiber diet can alter the gut microbiome and increase the effectiveness of such therapies, while taking probiotics can do the opposite.
A high-fiber diet promotes a greater variety of gut microbes, which in turn is associated with better outcomes with PD-1 therapy, according to research scientist Christine Spencer of the Parker Institute for Cancer Immunotherapy in San Francisco. At the same time, probiotic supplements or tablets that are supposed to contain beneficial bacteria actually reduce microbial diversity in the gut of cancer patients. The results were announced at a press conference held by the American Association for Cancer Research.
Tumors in only 20-30% of cancer patients stop growing or shrink with PD-1 therapy. Spencer and her colleagues had previously determined that bacteria from the Ruminococcaceae family improved the body's response to treatment, but the researchers did not know at the time why some people had more of these beneficial bacteria than others.
Diet is one way to change the human microbiome - the collection of bacteria, fungi, and other microbes living outside and inside the body. Spencer and colleagues surveyed 113 people with melanoma about what they eat, including probiotic use, and collected stool samples from each of those interviewed.
46 percent of patients who ate a high fiber diet, including fruits, vegetables, and whole grains, had more bacteria associated with responses to immunotherapy. Moreover, these same patients were more likely to have a positive response to therapy. Participants who ate more processed meat and too much sugar had fewer of these bacteria, and their tumors continued to grow despite treatment.
More than 40% of patients said they were taking probiotics. These individuals had less gut microbial diversity than those who did not take the supplements.
The new study is yet another in a growing body of recent research indicating probiotics are probably not as beneficial as doctors and patients thought.
While the evidence is preliminary, research suggests there are ways to improve the outcome of immunotherapy for cancer patients. Numerous studies have already pointed out the link between high-fiber diets and a lower risk of cancer, as well as other beneficial effects.