The Link Between Fructose and Weight Gain

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Sugar isn't always sweet—at least not to your waistline.

Added sweeteners have been blamed, at least in part, for our nation's obesity epidemic, with sugary beverages and virtually anything containing high-fructose corn syrup getting an especially bad rap. But how does fructose contribute to weight gain? We found out.

In a new study published in today's issue of the Journal of the American Medical Association, researchers from Yale University School of Medicine analyzed the brain activity of 20 healthy, normal weight adults to investigate the link between simple sugar consumption and weight gain.

After ingesting a drink made from either glucose or fructose, study participants underwent two magnetic resonance imaging sessions to see how their brains reacted to each sugar. Changes in an appetite-controlling region of the brain, called the hypothalamus, and its cerebral blood flow were tracked and measured after consuming each drink.

What the researchers found was interesting: Not all sugars are created equal. In fact, participants experienced a significant reduction in hypothalamic blood flow after glucose versus fructose consumption. Meaning, glucose reduced activity in the brain that regulates appetite and satiety. Fructose, on the other hand, did quite the opposite.

"Participants were accompanied by sensations of greater fullness after drinking only glucose, but they were not as full after they drank the fructose," explains Jonathan Q. Purnell, M.D., who wrote the commentary that appears with the study. "This gave us some insight as to why fructose might increase food intake and weight gain."

In other words, fructose may make it harder to get a grip on overeating. This, Dr. Purnell says, is especially concerning to our nation's health because we are continually exposed to more and more foods that contain fructose.

So while we know that virtually anything made with corn syrup or other high-fructose foods, such as baked goods, soda and sports drinks, are not exactly slimming for our waistline, does this mean that healthier high-fructose foods such as fruit are the pits, too?

Not by any stretch, according to Purnell. "This study doesn't apply to eating fruits," he notes. "You can think of fructose as nature's natural sweetener, but fruit is also high in water content, fiber and nutrients. It's not the same as having a fructose-sweetened beverage, so we would never say don't eat fruit."

The take-home? "Fructose improves the quality and look of processed foods, but we need to go back to what we used to do: buy whole foods, whole grains and cook and eat simply," adds Purnell.

If you can't eliminate your consumption of sweetened drinks and baked goods—the two items Purnell notes are notoriously high in fructose—then at least cut back. And if you think you can separate glucose from fructose when doing so, you can't. These simple sugars are typically found together in anything that contains added sugar. "The added sugars have become so common now that we're being exposed to fructose in many more products. That makes a difference in how our brains respond—and ultimately, this impacts our weight."

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