Ingesting fructose can lead to brain activity that promotes overeating, according to a recent study conducted by researchers at the Yale School of Medicine.
The study, published Jan. 2 in the Journal of the American Medical Association, or JAMA, suggests that obesity is linked to consumption of fructose, a simple sugar found in foods containing high-fructose corn syrup. While consumption of glucose, another type of simple sugar, inhibits brain activity in regions that promote the desire to eat, the study suggests that fructose does not effectively suppress areas of the brain associated with food-seeking behavior. The researchers also noted that as fructose consumption has increased in recent decades, obesity rates have risen as well.
“When you consume sugar, it’s broken up into its components of fructose and glucose and then absorbed into the bloodstream,” said section chief of endocrinology at the Yale School of Medicine, Robert Sherwin, who led the study. “What we saw was that fructose could not suppress areas of the brain that regulate appetite.”
Sherwin’s team also found that glucose, unlike fructose, had an effect on circulating hormone levels, elevating the amount of insulin in the body and promoting fullness.
The researchers established a link between fructose and overeating by evaluating the response of normal-weight individuals to ingestion of glucose and fructose. They gave 20 adults between the ages of 20 and 40 beverages containing 75 grams of either fructose or glucose and then conducted MRI scans to track blood flow to their brains after ingestion. The researchers found that consumption of glucose, unlike fructose, reduced blood flow to the hypothalamus, insula and striatum, all regions of the brain that regulate appetite and promote the desire to eat.
“The findings were quite striking,” said Yale School of Medicine associate professor of endocrinology Jonathan Bogan ’86. “The implication is that fructose ingestion may not activate brain satiety mechanisms to the same degree as glucose, which may help explain how increased fructose consumption has paralleled societal increases in obesity and insulin resistance.”
In an editorial accompanying the study in JAMA, physicians Jonathan Purnell and Damien Fair of Oregon Health and Science University argued that the study’s findings have implications in the fight against obesity. They wrote that while weight loss is typically determined more by the number of calories than the types of foods consumed, Sherwin’s study demonstrates that the category of sugar ingested -— whether fructose or glucose — can be key in determining satiety.
“The calories are important, but if you’re eating foods that don’t make you full, you may consume more calories,” Sherwin said.
Sherwin’s research methodology distinguishes his study from others examining the factors contributing to obesity. According to Richard Kibbey, an assistant professor of endocrinology at Yale School of Medicine, most previous studies have been limited to testing rodent responses to fructose or evaluating human responses based on questionnaires, whereas Sherwin’s research physiologically examined brain activity.
“It was a novel idea to use neuroimaging to help us understand what is happening in the brain when we consume fructose,” said Yale School of Medicine pediatric endocrinologist Dr. Ania Jastreboff GRD ’11, who has worked with Sherwin in other research studies. “Dr. Sherwin’s research methods are impeccable. He is so careful in how he designs his studies and carries them out.”
Because MRI scans do not provide direct measures of neural activity, the study did not offer any clinical conclusions, but rather showed a general trend between fructose consumption and obesity.
Sherwin and his colleagues cautioned that the study was only a first step in the process of differentiating between fructose and glucose consumption. Researchers are now testing obese people to see if their reactions to fructose ingestion are similar to that of normal-weight people.
“Frankly, you can’t readily go in and measure neural activity in living humans,” Kibbey said. “This study is a research tool and people can use it in the future to determine whether there is a physiological difference between fructose and glucose in terms of neural response.”
Given the study’s limitations, the American Beverage Association downplayed the significance of the research findings, according to an email they sent to CBS News.
“These findings should be kept in perspective,” the ABA wrote. “The researchers gave 20 adults a beverage sweetened with either fructose or glucose — neither of which are found alone in any sweetened beverage.”
Sherwin said that he recognizes the study, which he and his colleagues began planning three years ago, is only the first step in a long research process analyzing eating behaviors contributing to obesity. He called the study a “teaser” that he hopes will encourage public discourse about food consumption.
The average age of the subjects examined in the study was 31.