02.28.11 9:11 AM ET
The Fight Over High-Fructose Corn Syrup
The debate over high-fructose corn syrup (HFCS) comes down to this: the corn refiners who make it and the food manufacturers who put it into sodas, baked goods, salad dressing, and hundreds of other products argue—in ads and elsewhere—that a calorie is a calorie. It doesn't matter, they say, whether that calorie comes from table sugar (sucrose) or HFCS. Each has 16 calories per teaspoon. Public-health officials and some scientists, on the other hand, aren't so sure the two sweeteners are equivalent.
Gallery: Foods With High-Fructose Corn Syrup
Now a stream of studies shows that sugar and corn sweeteners differ in important ways, including how they affect the appetite-control centers in the brain. That suggests that HFCS may be partly responsible for the obesity epidemic. (In all, the average American consumes 140 pounds of high-fructose sweeteners, including corn-based sweeteners, a year.) Research to be published in March adds to growing evidence that the brain and body treat the two sugars differently.
The new study is too small to decide the question—it included only nine people—but it fits with other research on both humans and lab animals. Scientists led by Jonathan Purnell of Oregon Health & Science University gave fructose, glucose, or salt water to volunteers and then measured brain activity with functional MRI scans. Over several regions of the cortex, activity increased in people given glucose but decreased in those given fructose, the scientists will report in Diabetes, Obesity and Metabolism. Cortical regions that responded differently included the orbital prefrontal, a key player in the reward circuit, and regions that process the pleasurable effects of food. "It's evidence that fructose and glucose elicit opposite responses in the human brain," says Purnell.
The relevance to high-fructose corn syrup isn't clear-cut, though. HFCS contains at most 55 percent fructose and in some forms only 43 percent; almost all the rest is glucose. Sucrose is 50 percent glucose and 50 percent fructose. None of the sweeteners people eat are 100 percent fructose, which was used in the Oregon study and several others. "We always consume fructose with glucose," points out John White, a consultant in Illinois who was speaking for the Corn Refiners Association. Testing pure fructose as a stand-in for high-fructose corn syrup, he argues, might therefore produce misleading results.
That caveat comes with its own asterisk, however. When HFCS is made from cornstarch, the fructose molecules are not bound to other sugar molecules. Every fructose molecule in sucrose, in contrast, is bound to a glucose. White argues that whether fructose is bound or not is irrelevant, but the fructose in sucrose must go through an extra metabolic step before the body can use it. Treating fructose as a stand-in for HFCS might not be a bad approximation.
Such differences may explain the effects of HFCS in both lab animals and people. Rats eating equal calories from the two gained significantly more weight on HFCS than on table sugar, scientists led by Bart Hoebel of Princeton reported in 2010. The HFCS-fed animals also had increases in abdominal fat and triglycerides. And in a 2010 review, scientists at the University of California, Davis, noted that, in people, fructose added to abdominal fat and other measures "associated with increased risk for cardiovascular disease and type 2 diabetes." HFCS is not the sole culprit in obesity. But the body and brain don't seem to treat it as an innocent bystander, either.
Sharon Begley is the science columnist and science editor of Newsweek. She is the co-author of the 2002 book, The Mind and the Brain, and the author of the 2007 book Train Your Mind, Change Your Brain.