Reading labels reveals that many foods and beverages—even so-called healthy ones—contain fructose, often in the form of high-fructose corn syrup, as a sweetener. Health experts have long suspected that fructose is a factor in the nationwide obesity and diabetes epidemic, and new research from the Oregon Health & Science University supports the connection.

Researchers gave nine normal-weight study participants separate infusions of fructose and glucose (simple sugars) and then used magnetic resonance imaging to observe brain reactions. Glucose activated areas of the brain associated with regulating food intake and satiety—its “reward circuitry”—while fructose inhibited brain response in those areas.

The study concludes that this important difference may explain why fructose consumption, which deactivates the brain’s normal satiation response, appears to increase obesity and diabetes.