What Our Gut Bacteria Eat May Influence How Well Cancer Immunotherapy Works

The composition of gut bacteria could play a role in how effective cancer immunotherapy treatments are, according to a study published in Nature. Researchers found that certain diets usually associated with obesity may actually boost the effectiveness of these treatments in mice. This "obesity paradox" puzzled scientists until they discovered a possible link between the food we eat and the microbes living in our digestive tracts.

Obesity is linked to an increased risk of various cancers and poorer outcomes overall. However, some studies have shown that patients with a higher body mass index often respond better to immune checkpoint inhibitors, a type of cancer drug that helps unleash the immune system against tumors. This phenomenon, known as the "obesity paradox," has been difficult to explain.

To investigate, the researchers examined 12 different diets in mice, assessing how they affected metabolism, immune activity, gut microbiome, and responses to checkpoint inhibitors. Some obesity-promoting diets seemed to improve immunotherapy responses, even after a relatively short exposure. The benefits were not correlated with metabolic dysfunction, suggesting a more complex relationship between diet, bacteria, and treatment.

Further experiments in germ-free mice revealed that pairing a bacterium called Lactobacillus johnsonii with an obesity-promoting diet helped drive tumor regression. This combination increased bacterial metabolites derived from aromatic amino acids, which seemed to enhance treatment efficacy. The findings suggest that specific bacteria and the food they consume can work together to influence the effectiveness of cancer immunotherapy.

The team also transferred gut microbes from human donors into mice. Donors with a higher BMI produced microbes that improved treatment efficacy compared to those from donors with a normal BMI. This indicates that the composition of gut bacteria itself, rather than just body size, may be important.

While the results are promising, researchers caution that these findings are in the early stages. They plan to identify the specific biological effects of this bacterial-food pairing and determine if these effects can be reproduced safely. Until then, cancer patients should still consult with their healthcare team before making any significant changes to their diet.

The study offers new insight into the complex relationship between diet, gut bacteria, and cancer immunotherapy, but it should not replace professional medical advice.