Eating certain types of fiber may help lower blood sugar in people with type 2 diabetes by feeding good gut bacteria, but it doesn’t work the same for everyone, especially if they’re already taking metformin.

This study looks at multiple human trials and says that eating certain fibers (like inulin) may slightly lower blood sugar in diabetics and change gut bacteria in helpful ways — but the results aren’t the same for everyone, and medicines like metformin might affect the outcome.