All sugars are not created equal when it comes to how our bodies metabolize the sweeteners, a new study suggests.

People who drank beverages sweetened with fructose, but not glucose, showed an increase in intra-abdominal fat and blood lipid levels and decreased sensitivity to the hormone insulin, researchers reported in this week's issue of the Journal of Clinical Investigation.

The findings suggest that fructose-sweetened beverages can interfere with how the body handles fat, leading to medical conditions that increase susceptibility to heart attacks and strokes.

The results could be important given that in 2005, the average American consumed 64 kilograms of added sugar, a sizeable proportion of which came through drinking soft drinks, said study author Peter Havel of the University of California at Davis and his colleagues.

Consumption of sugars and sweeteners in the U.S. went up by 19 per cent between 1970 and 2005, according to a commentary accompanying the study.

Increased use of high-fructose corn syrup as a sweetener in pop in the last few decades has been proposed as one dietary change fueling obesity in developed countries, Matthias Tschöp and Susanna Hofmann of the University of Cincinnati-College of Medicine noted in their commentary.

The most common form of the syrup contains five per cent more fructose than glucose and is perceived as sweeter, according to food and drink manufacturers.

Metabolic changes

In the 10-week study, 17 subjects consumed a quarter of their calories from fructose-sweetened beverages and another 15 subjects drank the equivalent amount in glucose-sweetened beverages. Participants had an average age of 50 and a body mass index of 29, which is considered overweight.

Both groups put on the same amount of weight, but only the fructose group showed the other differences.

People drinking the equivalent of about six cans of soft drinks a day in fructose became less sensitive to insulin, which helps control glucose levels in the blood, and showed signs of dyslipidemia such as high cholesterol.

Fructose is no worse than glucose if taken in moderation, said Dr. David Jenkins, who holds the Canada Research Chair in nutrition and metabolism at the University of Toronto.

"We're talking about excess in people who are gaining weight, people who are overweight to begin with and people who are not exercising to begin with," Jenkins said.

The long-term effects of fructose remain unknown, but it's clear that chronic overconsumption of dietary sugars in general is harmful to health, the commentators said.

"For our part, we will continue to aim for moderation of balanced caloric ingestion without excluding the occasional sweet soda," they concluded.

Some manufacturers have released sugar-free versions of soft drinks, and the corn industry has responded with ads suggesting high-fructose corn sweeteners have "the same natural sweeteners as table sugar."