Fructose affects brain in a way that causes overeating, scientists find

First Posted: Jan 03, 2013 02:48 PM EST

Fructose doesn't appear to trigger a feeling of fullness in the human brain, and could thus lead to overeating and obesity, according to a new study from scientists at Yale University.

The study used magnetic resonance imaging of the brain to show that fructose intake didn't reduce blood flow in areas of the brain that control appetite -- while subjects who ingested glucose, another simple monosaccharide that is less sweet than fructose but can be directly used as fuel by body cells, including the brain. All three dietary monosaccharides, which includes galactose as the third one, are absorbed directly into the bloodstream during digestion.

The consequence of this effect is that subjects who ingested purely fructose were told by their brains that they were still hungry. "It's probably not in your best interest to have high fructose-containing drinks because they're not going to cause you to be full, and you'll tend to consume more calories," said Robert Sherwin, a professor of medicine at Yale University School of Medicine.

The study, published in the Journal of the American Medical Association, found that subjects' personal experience of their own hunger were consistent with the results from the brain scans.

"If you don't turn off the areas of the brain that are driving you to eat, you have a tendency to eat more than you would," commented Sherwin on this relation. Other researchers commenting on the study agreed: "It implies that fructose, at least with regards to promoting food intake and weight gain, is a bad actor compared to glucose," said Jonathan Purnell, an endocrinologist at Oregon Health & Science University.

Both sugars are produced naturally in fruits, vegetables and wheat's, but fructose is sweeter and cheaper to produce than glucose, and has other commercial advantages including a longer shelf life and resistance against freezing. Thanks to mass production of sugar cane and corn in South- and North-America, sugar in general became a major ingredient for the American food industry, and thus the American diet.

Government regulations that set the price of table-sugar higher than in other countries, coupled with an excess of corn in the American market led to the development of high-fructose corn syrup (HFCS), a concentrated and inexpensive sweetener produced by adding fructose to corn syrup. In the U.S., consumption of high fructose corn syrup increased dramatically from 1970 to the present day, with a 1,000 percent increase from 1970 to 1990 alone, according to "Consumer Reports". The product is found in many beverages, including nearly all non-diet soda brands, as well as breakfast cereals, salad dressings, cheese spreads, yogurts, jams, peanut butter and other foods.

On the other hand, "normal" table-sugar, or sucrose, consists of equal amounts of fructose and glucose as well, just like HFCS. The difference might be that HFCS is cheaper and can be more easily applied to a wide variety of foods, increasing its share in the diet.

In this context, the study results are relevant at a time when obesity is a wide-spread health problem for the population, with two-thirds of American adults obese, as well as one-third of American children - and similar issues in many other parts of the world.

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