Feb 20, 2012 10:06 PM
Feb. 20, 2012 -- When it comes to weight gain, fructose should not be singled out for blame, a new review of the scientific literature suggests.
The review, in the Annals of Internal Medicine, shows that excessive calories -- and not any unique properties of fructose -- are more likely to lead to extra pounds.
"Is fructose really the source of all metabolic evil?" says researcher John Sievenpiper, MD, PhD, of McMaster University in Hamilton, Ontario, Canada. "From our standpoint, it does not look like it is."
However, the authors acknowledge that many of the studies they reviewed had serious shortcomings. Therefore, their conclusions are, in a word, inconclusive.
"Overall, the evidence from our analysis is too preliminary to guide food choices in the context of real-world intake patterns," they write.
The review drew upon a large number of studies, each of which falls into one of two types.
Thirty-one of the studies divided the participants into two groups. Each group consumed the same amount of calories, but one group ate fructose while those in the other group ate a different type of carbohydrate. Doing so allowed the researchers to isolate fructose in order to determine its effect on body weight change. They found none.
The remaining 10 studies under review were based around adding calories. In each, half of the participants ate their usual diet, while the other half added fructose, a naturally occurring sweetener, to what they normally ate. The fructose groups did gain weight, but no more than would be expected from the amount of additional calories -- or energy -- that they took in as part of the studies.
"Energy seems to be the dominant factor," Sievenpiper says. "There was no effect from fructose."
The review is likely to be controversial because increased fructose consumption has been targeted as a leading cause of the obesity epidemic, particularly in the form of high fructose corn syrup, a sweetener added to non-diet soft drinks and many other food products. Sievenpiper, however, says the debate over fructose misses the point.
"We feel the controversy has directed the issue away from over-consumption. Our data suggests that fructose plays the same role as any energy-dense substance."
Cleveland Clinic's Laura Jeffers, MEd, RD, LD, agrees.
"Fructose may not be the villain," says Jeffers, who reviewed the study for WebMD. "People should be aware of the total calories they're consuming rather than worrying about one type of sugar."
But do we need another study telling us that? No, says David Heber, MD, PhD, director of the UCLA Center for Human Nutrition.
"It's much ado about nothing," says Heber, who says that we should be focusing on how much fructose we consume and where we get it.
"There's too much fructose in our diets, and it's not coming from fruits and vegetables," says Heber, who was not involved in the study. "If fructose comes from those things, I have no problem with it."
Sievenpiper says his team's study was based on the "highest level of evidence available," but adds that "most of the trials had methodology issues, were too short, [and] were of poor quality. We don't think that this group of studies is particularly representative of real-world situations."
He would like to see large, long-term trials that may be better able to determine whether fructose itself -- rather than simply the amount of calories -- plays a particular role in weight gain.
"The studies need to be done in real-world formats," he says.
That means looking at the high fructose corn syrup that's added to so many products, at the fructose found in fruits and vegetables, and at the means by which fructose is consumed, such as in sweetened soft drinks.
"Energy in fluid form does not tend to be compensated," he says, meaning that it adds calories to the diet but does not satisfy hunger as well, which can easily lead to overindulgence. "Maybe the format is important."
Sievenpiper and his team received funding from several outside sources, including the Coca-Cola Company and the Calorie Control Council, a trade group that represents the diet food and beverage industry. However, he says that none of the funders had access to his data or influenced the review in any way.