MARQUETTE - Scientists have used imaging tests to show for the first time that fructose, a sugar that saturates the American diet, can trigger brain changes that may lead to overeating.
After drinking a fructose beverage, the brain doesn't register the feeling of being full as it does when simple glucose is consumed, researchers found.
It's a small study and does not prove that fructose or its relative, high-fructose corn syrup, can cause obesity, but experts say it adds evidence they may play a role. These sugars often are added to processed foods and beverages, and consumption has risen dramatically since the 1970s along with obesity. A third of U.S. children and teens and more than two-thirds of adults are obese or overweight.
High fructose corn syrup is listed as an ingredient on a can of soda in Philadelphia. Scientists have used imaging tests to show for the first time that fructose, a sugar that saturates the American diet, can trigger brain changes that may lead to overeating. The study, in the Journal of the American Medical Association, does not, however, prove that fructose or its relative, high-fructose corn syrup, can cause obesity. But experts say it adds evidence they may play a role. (AP photo)
All sugars are not equal - even though they contain the same amount of calories - because they are metabolized differently in the body. Table sugar is sucrose, which is half fructose, half glucose. High-fructose corn syrup is 55 percent fructose and 45 percent glucose. Some nutrition experts say this sweetener may pose special risks, but others and the industry reject that claim. And doctors say we eat too much sugar in all forms.
Dr. James Surrell, a digestive health specialist with Marquette General Hospital, said he cautions patients against all refined sugars, but also tells them to be wary of too much of any sugar, which the body utilizes for immediate energy needs.
"The body will never waste sugar, it will never push it out of the body," he said. "Once our immediate needs are satisfied, our body has to do something with the excess sugar."
Sugar that is not immediately converted into energy, then, is converted into fat, Surrell said.
He said he has preached against fructose for years, as he feels it causes weight gain. He was surprised, however, to hear that it may actually stimulate appetite.
For the study, scientists used magnetic resonance imaging, or MRI, scans to track blood flow in the brain in 20 young, normal-weight people before and after they had drinks containing glucose or fructose in two sessions several weeks apart.
Scans showed that drinking glucose "turns off or suppresses the activity of areas of the brain that are critical for reward and desire for food," said one study leader, Yale University endocrinologist Dr. Robert Sherwin. With fructose, "we don't see those changes," he said. "As a result, the desire to eat continues - it isn't turned off."
What's convincing, said Dr. Jonathan Purnell, an endocrinologist at Oregon Health & Science University, is that the imaging results mirrored how hungry the people said they felt, as well as what earlier studies found in animals.
"It implies that fructose, at least with regards to promoting food intake and weight gain, is a bad actor compared to glucose," said Purnell. He wrote a commentary that appears with the federally funded study in Wednesday's Journal of the American Medical Association.
Researchers now are testing obese people to see if they react the same way to fructose and glucose as the normal-weight people in this study did.
What to do? Surrell suggested avoiding refined sugars whenever possible. Eat whole fruits and vegetables, which have plenty of natural sugars and if you want to drink soda, opt for the diet variety, he said. Additionally, Surrell said, water is very important to the human body, and the average person should drink four pints per day.
Kyle Whitney can be reached at 906-228-2500, ext. 250.