The gut microbiome composition of individuals with prediabetes shows a stronger statistical association with metabolic clusters defined by age, BMI, HbA1c, insulin resistance, and beta-cell function than with traditional diagnostic categories based solely on glucose levels.

The types of bacteria in the gut form a network that can be either stable or fragile. In people with prediabetes, a fragile network allows fiber to trigger a chain reaction: bacteria break down fiber into chemicals that signal the gut to release a hormone, which tells the pancreas to release more insulin. This improves blood sugar control and reshapes the metabolic profile. People with a stable bacterial network don’t respond to fiber, so their metabolic profile stays unchanged. The specific mix of bacteria present before eating fiber predicts whether this whole process will happen.