In a new study from the National Cancer Institute, researchers found a diet rich in fiber may help some people being treated for melanoma respond to immunotherapy treatment by influencing the gut microbiome.
They found among patients with melanoma who underwent immunotherapy with immune checkpoint blockers, those who consumed at least 20 grams a day of dietary fiber survived the longest without their disease progressing.
In contrast, use of probiotic supplements appeared to lessen somewhat the effectiveness of immune checkpoint blocker regimens.
Probiotics are live microorganisms typically consumed as a supplement to improve gut health.
Immunotherapy with immune checkpoint blockers helps restore the immune system’s natural ability to recognize and kill tumor cells.
These drugs have been transformative in melanoma, improving how long some people with advanced disease live, sometimes by years.
Several studies have suggested that the composition of the bacteria in the gut may influence the response to immunotherapy.
In a previous study, the team showed that people with melanoma who initially did not respond to treatment with an immune checkpoint blocker did respond after receiving a fecal transplant from a patient who had responded to the drug.
The fecal transplant, they concluded, had introduced different gut bacteria that helped make it easier for immune cells to invade and kill their tumors.
In the study, the team looked at the composition of fecal microorganisms (the gut microbiota), dietary habits, and probiotic supplement use among patients who were being treated for advanced melanoma with immune checkpoint blockers.
Among the 128 patients whose dietary fiber intake was known, those who reported consuming at least 20 grams of dietary fiber per day lived longer without their cancer progressing than those who consumed less dietary fiber.
Every 5-gram increase in daily dietary fiber intake corresponded to a 30% lower risk of progression of the disease.
The researchers also looked at the impact of dietary fiber on the response to treatment with anti-PD-1 drugs, a category of immune checkpoint blockers, in mouse models of melanoma.
They found that the diet is affecting the response to immune checkpoint therapy by changing the composition of the gut microbiota.
The team says that one possible mechanism through which dietary fiber exerts its beneficial effect is by increasing the types of bacteria in the gut, such as Ruminococcaceae, that produce high levels of certain short-chain fatty acids that have an antitumor effect.
The researchers also looked at the impact of probiotics on gut bacteria in the mouse model of melanoma.
Mice fed probiotics had a reduced response to treatment with anti-PD-L1 drugs and developed larger tumors than control mice.
Further analysis showed that mice fed probiotics had lower levels of tumor-killing immune cells, suggesting a weakened immune response.
In the human study, the team found that patients who consumed the highest levels of dietary fiber with no probiotic use survived the longest.
These results suggest that one can target the composition of the gut microbiota and affect the ability of the patient to respond to immunotherapy.
The team says consuming a diet rich in fiber, like fruits, vegetables, and legumes, could improve your ability to respond to immunotherapy.
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The study is published in Science. One author of the study is Giorgio Trinchieri, M.D.
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