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Sugars in the Brain continued...

After the glucose drink, the body seemed to recognize and respond to the extra calories with an increase in glucose and insulin levels. That response, which blunts hunger, was significantly greater than fructose's. Brain activity also slowed in the hypothalamus, the region that stimulates appetite.

After the fructose drink, on the other hand, the hypothalamus continued to stay active. There was little increase in insulin, and study volunteers said they felt hungrier, even though they weren’t told which sugar they’d had.

Other hormones that are known to regulate hunger, such as ghrelin and leptin, were unchanged after ingestion of either type of sugar.

“When we eat, the body recognizes that food is coming in, and ultimately the brain is trying its best to regulate how many calories we need and how much fat we have in our bodies, and trying to maintain a balance so that we’re not overeating or under-eating,” Sherwin says. 

Fructose seems to upset that balancing act, though researchers aren’t sure why.

One theory is that when humans evolved, the problem wasn’t overeating, but not getting enough calories. In that case, it wouldn’t have been a good idea for fructose, which is the primary sugar in fruit and fruit juices, to make us feel full since fruits may have been a primary food source.

That may have worked fine for cavemen, but it may not be so great for our sugar-saturated modern diets.

Advice to Dieters

So what does the study mean for health-conscious eaters?

That’s harder to say, says Jonathan Purnell, MD, an endocrinologist at Oregon Health & Science University in Portland.  Purnell wrote an editorial on the study but was not involved in the research.

“This study didn’t prove that fructose causes weight gain,” Purnell says. “It doesn’t reflect real-world conditions.”

Industry representatives agree.

“When consumed together, as they almost always are, fructose and glucose balance each other out and would likely have no effect on normal hypothalamic blood flow,” says James Rippe, MD, professor of biomedical sciences at the University of Central Florida and a paid consultant for the Corn Refiners Association, the group that represents manufacturers of high-fructose corn syrup.

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