Rresearchers at the University of California at Davis have found that fructose, but not glucose, causes alarming changes in increased intra-abdominal fat (belly fat), triglyceride levels, and insulin sensitivity.

The researchers suggest that people with metabolic syndrome (a blend of conditions including belly fat and insulin resistance) should avoid fructose-containing beverages. Fructose is found in fresh fruit, fruit juice, and preserves. But much of it sneaks into our diets though high-fructose corn syrup (HFCS) in soft drinks.

Both sucrose (table sugar) and high-fructose corn syrup (HFCS) are broken down into fructose and glucose when eaten, and both have been under suspicion as contributing to obesity and insulin resistance. (This study looked only at pure fructose, not HFCS or sucrose.)

In the study, overweight and obese volunteers ate identical balanced diets for two weeks and then spent ten weeks with 25% of their calories coming from either fructose or glucose. While both groups gained an average of 3.3 pounds, only the fructose group had increased intra-abdominal fat (internal fat linked to disease risk).

The fructose group also had raised levels of fatty triglycerides (which gets deposited as intra-abdominal fat) and cholesterol, and they had 20% less insulin sensitivity. The glucose group showed none of these negative results.

In a separate study, the researchers tested blood triglyceride levels after people consumed a meal with 25% of the calories from HFCS, sucrose, fructose or glucose. All sugars except for glucose caused elevated levels 24 hours after the meal.