People who consume the artificial sweetener sucralose are less likely to respond to cancer immunotherapy, suggesting the sweetener may blunt the treatment’s effects.

Immunotherapy helps the immune system detect and destroy cancer cells, making it a crucial treatment for numerous cancers. “When it works, it works very well. Patients can be disease free and go about their lives and live for years and years,” says Abigail Overacre-Delgoffe at the University of Pittsburgh in Pennsylvania. “Unfortunately, immunotherapy doesn’t work for all patients, and in many cancer types, it only works for the minority of patients.”

It isn’t clear why that is, though numerous studies indicate the gut microbiome plays a role, as it helps regulate immune responses. Previous research has also shown that artificial sweeteners can change the composition of gut microbes in humans.