Scientists have uncovered an unexpected connection between diet and cancer treatment. In a surprising finding, certain diets typically considered “unhealthy” or “fattening” actually improved responses to a common form of cancer immunotherapy in mice.
The discovery suggests that the success of cancer treatment may depend not only on which bacteria live in the gut, but also on the foods that help those bacteria thrive.
“There is a synergistic relationship between the bacteria that reside in our GI tract, and the food we eat,” said Daniela Quail, Associate Professor in the Department of Physiology and Principal Investigator at the Rosalind & Morris Goodman Cancer Institute.
“Even with the right composition of bacteria in your gut, the foods you eat to nourish those populations can determine whether or not you respond to treatment,” said Quail.
Quail co-led the research, which examined how diet influences the effectiveness of immune checkpoint inhibitors. These widely used immunotherapy drugs help the immune system recognize and attack cancer cells. Other senior researchers involved in the study included McGill scientist Logan Walsh and CR-CHUM collaborators Bertrand Routy and Arielle Elkrief. The findings were published in Nature.
Why Unhealthy Diets Produced Surprising Results
One of the most unexpected discoveries was that some diets associated with weight gain appeared to make immunotherapy more effective, challenging assumptions about the relationship between nutrition and cancer treatment.
“Our findings were surprising because they highlighted a benefit of some obesogenic diets,” she said. “That tells us the relationship between diet and cancer treatment is more complex than a simple message to eat healthy and exercise.”
However, the researchers emphasize that these results should not encourage cancer patients to consume diets that promote obesity. Excess weight carries established health risks, and the findings do not demonstrate that adopting such diets would improve cancer treatment in humans.
Instead, the scientists want to understand how different foods influence the gut microbiome, the enormous community of trillions of bacteria that inhabit the digestive system. Identifying the mechanisms responsible for the improved treatment responses could eventually help researchers develop safer ways to make cancer immunotherapy more effective.
A New Explanation for Cancer’s Obesity Paradox
The investigation grew out of a longstanding puzzle in cancer research known as the “obesity paradox.”
Obesity is generally linked to a greater risk of developing cancer and dying from the disease. Yet several studies have found that cancer patients with a higher body mass index (BMI) sometimes respond more favorably to immune checkpoint inhibitors.
To investigate this apparent contradiction, the research team tested 12 different diets in mice. Surprisingly, some diets associated with obesity improved the animals’ responses to immunotherapy, even when they were consumed for relatively short periods.
These results suggest that the apparent treatment advantage associated with obesity may not be primarily caused by excess body weight. Instead, the explanation could involve the combined influence of diet and gut bacteria on the immune system.
By uncovering how these interactions affect cancer treatment, researchers hope to identify new approaches that reproduce the beneficial effects without exposing patients to the health risks associated with obesity.
About the Study
The study, “Diet-microbiome synergy underlies obesity-associated immunotherapy efficacy,” was published in Nature by McGill PhD graduate Lysanne Desharnais, Daniela Quail, and their collaborators.
Funding was provided by the Canadian Institutes of Health Research, the Canadian Cancer Society, the Terry Fox Research Institute, the Canada Foundation for Innovation, and philanthropic supporters including La Vie en Rose and the Bachynski Family Foundation.
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