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We know that eating a balanced diet of whole foods rich in plants and high in nutrients, vitamins and fiber is good for us generally. While undergoing cancer treatments, healthy eating can also help patients feel their best and manage treatment side effects.

But could diet impact how well you respond to your cancer treatment?

A growing body of research suggests that nutrition could be another piece of the treatment puzzle. This is the field of nutrivention: nutrition as an intervention.

Researchers at MD Anderson are leading the way with studies like the Diet and Immune Effects Trial (DIET), led by physician-scientist ¡°Nutrivention is about not just using diet to improve quality of life but actually synergizing diet with cancer therapy to improve treatment outcomes,¡± says McQuade.

Designing the DIET study

The DIET study looked at patients with melanoma who were receiving immune checkpoint blockade (ICB) therapy, a type of immunotherapy.

¡°We had previously found that patients regularly consuming insufficient dietary fiber were less likely to respond to immunotherapy,¡± McQuade says. ¡°But we didn¡¯t know whether a dietary intervention could favorably impact cancer patients¡¯ immunotherapy responses.¡±

Patients were randomly assigned to either a control or experimental group. Both groups started at 20 grams of fiber per day ¡ª the average fiber intake of the US population. The control group stayed at that amount of fiber, as a healthy control diet, while the experimental group ramped up to 50 grams of fiber per day over 10 weeks.

The study provided participants in both groups with all of their food for the length of the study from MD Anderson¡¯s metabolic kitchen in the Bionutrition Research Core, directed by ¡°This is what¡¯s called a ¡®fully controlled feeding¡¯ study, and it¡¯s the gold standard of dietary intervention studies because it¡¯s not dependent on behavioral changes,¡± says McQuade. Otherwise, it might not be clear if results ¡ª or lack of results ¡ª from the study are because a high fiber diet isn¡¯t impactful, or because participants weren¡¯t able to fully adhere to the diet.

Study results show increased fiber intake improves immunotherapy response

After the 10-week intervention, McQuade¡¯s team measured immunotherapy response rates of patients in the two groups.

¡°We saw marked improvement in response to immunotherapy in patients in the high fiber group,¡± says Yufan (Simon) Qiu, M.D., Ph.D., a postdoctoral research fellow in the McQuade Lab presenting results from the DIET study at the 2025 American Society of Clinical Oncology (ASCO) Annual Meeting.

The high fiber group had a 77% objective response rate ¡ª the proportion of patients who had either a partial or complete response to the therapy ¡ª compared to just 29% in the control group. ¡°Removing the behavioral component of the study by providing patients with all of the food allowed us to really rigorously test dietary fiber as an intervention,¡± says McQuade.

Why is fiber important?

You might be wondering how eating more fiber can lead to an impact on your response to immunotherapy. To understand why, we turn to the gut microbiome.

Your gut microbiome is made up of all the microorganisms living in your intestines. Researchers study what kinds of microorganisms are in each person¡¯s gut microbiome and in what proportions. Jennifer Wargo, M.D., director of the Platform for Innovative Microbiome and Translational Research (PRIME-TR) at MD Anderson, previously found that patients who are more likely to respond to immunotherapy have different gut microbiome ¡®signatures¡¯ than those who are less likely to respond.

¡°Patients who were more likely to respond to immunotherapy had more of a particular type of bacteria that helps us digest fiber that is otherwise undigestible to us,¡± McQuade explains. By increasing the fiber in our diets, we essentially feed those beneficial bacteria. The bacteria make metabolites, which are products of their breakdown of the fiber, and those metabolites can impact immune response.