(Bloomberg) — Fructose, a sweetener found in many processed foods, may contribute to weight gain and obesity because it has minimal effect on brain regions that control appetite, a study by Yale University researchers conclude.

The research, published last week in the Journal of the American Medical Association, is the first to compare the human brain’s response to both fructose and glucose, two types of simple sugars used separately and together to sweeten food.

Scientists have long suspected that increased consumption of food flavored with fructose, a substance sweeter to the taste than glucose, may contribute to the U.S. obesity epidemic. In the Yale study, researchers used brain imaging to measure activity after the sweeteners were consumed. They found that only glucose had the ability to reduce blood flow in areas of the brain that regulate appetite, stopping people from wanting to eat more.

The data “surely suggest that 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,” says Robert Sherwin, a professor of medicine at Yale University School of Medicine in New Haven, Conn.

The brain requires glucose as a fuel, Sherwin says. When there isn’t enough in the body, it turns on cells to try to get a person to eat more. Once glucose levels rise, the brain turns those cells off. The study found that fructose doesn’t have the ability to operate that off switch, he says.

“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,” Sherwin says.

Better understanding of how certain foods and obesity affect the brain and body is important, researchers have said, at a time when the number of obese American adults has more than doubled in the past 30 years to about 78 million. The study results could be an important communications tool for employers who have implemented workplace wellness programs to help employees gain control of their health and nutrition.

The study included 20 healthy adults who underwent Magnetic Resonance Imaging. The researchers found a “significantly greater” reduction in blood flow after glucose ingestion, reducing activation of the hypothalamus, insula and striatum, brain areas that regulate food motivation and reward processing.

Glucose, the main type of sugar in the blood, is the top source of energy for the body’s cells. It comes from fruits, vegetables and other foods we eat, such as starches that the body breaks down into glucose. The healthiest source for glucose is natural complex carbohydrates like fruits and vegetables, Sherwin says.

Fructose is largely derived within the food industry from sugar cane, beets and corn. It’s added to foods and drinks because it is so sweet, helping food maintain its sweetness over longer periods of time and through the freezing process. While corn is also high in glucose, high-fructose corn syrup that’s added to processed foods, sodas, juices and sauces is made by adding fructose to corn syrup.

Jonathan Purnell, a professor of medicine at Oregon Health & Science University in Portland who wrote an accompanying editorial in the journal with colleague Damien Fair, says based on these results people should avoid processed and refined foods and drinks that contain fructose as well as glucose and eat more natural foods to reverse the trend in weight gain.

“It’s not that we are what we eat but what we eat influences what we become,” Purnell says. Future studies are needed to see what effect fructose has under real world conditions where people in the trial are eating and drinking typical foods.

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