MONDAY, December 27, 2021 (HealthDay News) – People on immune-boosting treatment for advanced melanoma may respond better if they follow a high-fiber diet, according to a new study.

The researchers said many more studies were needed, but their first results – in melanoma patients and lab mice – suggest that foods high in fiber may help via their effects on gut bacteria.

In contrast, there were signs that probiotic supplements might decrease this benefit.

The study – published on December 24 in Science – examined how diet and the gut microbiome might affect the response of cancer patients to immunotherapy – treatments that call on the immune system to help kill tumors.

The microbiome refers to the trillions of bacteria and other microbes that live naturally in the human body, much of it in the gut. These microbes are an integral part of the body’s normal processes – from metabolism and nutrient synthesis to brain function and immune defense.

In fact, cells of the immune system and gut bacteria are continually interacting, said Dr. Emeran Mayer, professor at the University of California, Los Angeles and author of The Gut-Immune Connection.

Gut bacteria play a key role in “educating and training” the immune system, said Mayer, who was not involved in the new study.

Fiber, on the other hand, is a factor in the makeup of the gut microbiome. It “feeds” certain types of bacteria, including those that produce short-chain fatty acids with anti-inflammatory and anti-tumor activity.

Previous research has suggested that the gut microbiome may influence the responses of cancer patients to immune checkpoint inhibitors. These drugs, such as Keytruda and Opdivo, are used to treat many types of cancer and work by releasing a particular “brake” on the immune system’s T cells, freeing them to find and attack cancer cells.

An intriguing question, then, is whether diet, including fiber, can alter patients’ responses to these treatments, said study author Dr Jennifer Wargo of the MD Anderson Cancer Center. University of Texas at Houston.

To investigate, his team studied 128 patients with advanced melanoma, the deadliest form of skin cancer.

Food questionnaires showed that 37 of these patients had “adequate” fiber intake – at least 20 grams per day from foods such as vegetables, fruits, beans and whole grains. The others received too little dietary fiber.

On average, according to the study, patients consuming enough fiber fare better: 76% responded to immunotherapy, compared to 60% of those on a low-fiber diet. This meant that their tumors had at least partially regressed or their cancer had remained stable for at least six months.

However, no such benefit was found among the 49 patients who reported using probiotic supplements. And the best response rate was seen in patients who ate a lot of fiber but didn’t take probiotics – at 82%.

None of this proves that the fiber was the reason.

The researchers then studied laboratory mice with melanoma. They found that giving the animals commercially available probiotic supplements interfered with their response to immune checkpoint inhibitors.

In contrast, a high-fiber diet slowed tumor growth in mice treated with the drugs and appeared to increase their T-cell activity. However, the high-fiber diet made no difference in mice without gut bacteria. According to Wargo, this suggests that the diet exerted its effects via the gut microbiome.

After being diagnosed with cancer, Wargo said, people often want to do something to take control and help support their treatment.

Sometimes they turn to supplements. But based on the current results, Wargo said, caution may be in order.

“People undergoing cancer treatment should discuss the use of probiotics with their healthcare team,” she said.

As for fiber, Mayer said more study is needed. He noted that there is “a lot of basic science” to support the idea that fiber could benefit cancer patients via the gut microbiome.

But to prove that, Mayer said, clinical trials will need to test the effects of adding fiber to patients’ diets. He noted that plant foods, the main source of dietary fiber, also contain other nutrients, including polyphenols, which could also be part of the story.

A trial testing the fiber is underway, Wargo said. Researchers are recruiting melanoma patients receiving immunotherapy and will randomly assign them to different amounts of dietary fiber, added to a healthy diet recommended by the American Cancer Society.

“This is the start of this research,” Wargo said. But ultimately, she added, studies on diet, gut microbes and immune function could have broad implications – not just for people with various types of cancer, but for everyone. .

For example, could some diets help people fight infections or respond better to vaccines, like those for the flu and COVID-19?

For anyone looking to support a healthy gut microbiome, Mayer said people should aim for a range of plant foods, as well as fermented foods like yogurt, fermented cottage cheese, kimchi and sauerkraut – which the research a linked to a greater diversity of intestinal bacteria.

Mayer noted, however, that it’s easier said than done for people who can’t afford or don’t have easy access to healthy, whole foods.

The Harvard School of Public Health has more information on nutrition and the microbiome.

SOURCES: Jennifer Wargo, MD, professor, genomic medicine and surgical oncology, University of Texas MD Anderson Cancer Center, Houston; Emeran Mayer, MD, PhD, professor of medicine and director, Oppenheimer Center for Neurobiology of Stress and Resilience, University of California, Los Angeles School of Medicine; Science, December 24, 2021