Is fructose（果糖） being unfairly blamed for the obesity epidemic? Or do we just eat and drink too many calories? Researchers from St. Michael's Hospital reviewed more than 40 published studies on whether the fructose molecule itself causes weight gain.

In 31 "isocaloric" trials they reviewed, participants ate a similar number of calories, but one group ate pure fructose and the other ate non-fructose carbohydrates（碳水化物） . The fructose group did not gain weight.

In 10 "hypercaloric" trials, one group consumed their usual diet and the other added excess calories in the form of pure fructose to their usual diet or a control diet. Those who consumed the extra calories as fructose did gain weight.

However, all that could mean is that one calorie is simply the same as another, and when we consume too many calories we gain weight, said the lead author, Dr. John Sievenpiper.

His research was recently published in the Annals of Internal Medicine.

"Fructose may not be to blame for obesity," he said. "It may just be calories from any food source. Overconsumption is the issue."

Fructose is naturally found in fruits, vegetables and honey. Participants in the studies examined by Dr. Sievenpiper ate fructose in the form of free crystalline（透明的） fructose, which was either baked into food or sprinkled on cereals or beverages.

The studies did not look at high-fructose corn syrup, which has been singled out as the main culprit for weight gain. It is only 55 per cent fructose, along with water and glucose.

Dr. Sievenpiper said the majority of studies they examined were small, of short-duration and of poor quality, so there is a need for larger, longer and better quality studies.