A new study conducted by doctors at Yale University School of Medicine and published in the January 2 issue of JAMA, the journal of the American Medical Association, has found evidence suggesting that consuming fructose affects regions of the brain that control appetite and feelings of satiety in ways that encourage overeating and lead to obesity, more than does consuming ordinary sugar (glucose).
Fructose is found in fruit as well as more and more commonly in processed foods. According to commentary published with the new study, since the 1970s there has been an economically driven trend of food processors — especially in the U.S. — increasingly to use the cheaper fructose found in high fructose corn syrup rather than the more expensive sugar (glucose) in producing processed foods.
“Increases in fructose consumption have paralleled the increasing prevalence of obesity, and high-fructose diets are thought to promote weight gain and insulin resistance,” the authors of the new study pointed out in an introductory abstract of their study. The purpose of the new study was to explore the specific mechanisms through which consuming fructose (rather than ordinary glucose) may lead to overeating and obesity.
The study, conducted by Kathleen A. Page, M.D., of Yale University School of Medicine, New Haven, Conn., and colleagues, used MRI imaging to compare changes in the brain chemistry of study participants who ingested a drink containing fructose with those of participants who ingested a drink containing glucose.
They found that glucose but not fructose increased blood flow to regions of the brain that control and cut off appetite, and that glucose but not fructose increased levels of insulin and other chemicals associated with a satisfied feeling. These mechanisms could explain how eating fructose, as opposed to ordinary sugar, could lead to greater appetite, increases in “food-seeking behavior,” overeating, and obesity.
The Study; Method
In the study, the researchers administered magnetic resonance imaging (MRI) brain scans to a group of 20 volunteers, some of whom were randomly assigned to consume a fructose-containing beverage, and the others of whom consumed a glucose-containing beverage. The MRI scans were given before and after consumption of the fructose or glucose drinks in two sessions spaced several weeks apart
The MRI’s measured relative changes in cerebral blood flow to the hypothalmus, insula, and striatum (“brain regions that regulate appetite, motivation, and reward processing,” according to the authors), after ingestion of fructose or glucose.
The researchers found, specifically, that “Glucose but not fructose ingestion reduced the activation of the hypothalamus, insula, and striatum—brain regions that regulate appetite, motivation, and reward processing; glucose ingestion also increased functional connections between the hypothalamic-striatal network and increased satiety.”
“There was a significantly greater reduction in hypothalamic CBF [cerebral blood flow] after glucose vs fructose ingestion,” the authors wrote. A reduction in blood flow within certain hypothalamic regions of the brain has the effect of turning off glucose-seeking cells that drive the body to eat, Dr. Robert Sherwin, a professor of medicine at Yale University School of Medicine and one of the authors of the study, explained to Bloomberg News.
“The brain requires glucose as a fuel,” Dr. Sherwin said. “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 said in a telephone interview with Bloomberg News.
“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,” Dr. Sherwin said.
In addition, “Glucose ingestion (compared with baseline) increased functional connectivity between the hypothalamus and the thalamus and striatum [associated with satiety - or feelings of being full and satisfied]. Fructose increased connectivity between the hypothalamus and thalamus but not the striatum,” the study authors reported.
Finally, “The disparate responses to fructose were associated with reduced systemic levels of the satiety-signaling hormone insulin and were not likely attributable to an inability of fructose to cross the blood-brain barrier into the hypothalamus or to a lack of hypothalamic expression of genes necessary for fructose metabolism,” the authors wrote.
In their conclusion, the authors wrote, “In a series of exploratory analyses, consumption of fructose compared with glucose resulted in a distinct pattern of regional CBF and a smaller increase in systemic glucose, insulin, and glucagon-like polypeptide 1 levels.”
In an editorial/ commentary accompanying the study, Jonathan Q. Purnell, M.D., and Damien A. Fair, PA-C, Ph.D., of Oregon Health & Science University in Portland, wrote, “these findings support the conceptual framework that when the human brain is exposed to fructose, neurobiological pathways involved in appetite regulation are modulated, thereby promoting increased food intake.”
What’s convincing, Dr. Purnell said, is that the imaging results mirrored how hungry the people said they felt, as well as what earlier studies had found in animals.
“[T]he implications of the study by Page et al as well as the mounting evidence from epidemiologic, metabolic feeding, and animal studies, are that the advances in food processing and economic forces leading to increased intake of added sugar and accompanying fructose in U.S. society are indeed extending the supersizing concept to the population’s collective waistlines,” Drs. Purnell and Fair concluded.
In an article published on September 12, 2012 (before the new study), Jennifer K. Nelson, R.D. of the Mayo Clinic, noted that “Controversy exists [at least at that time] about whether or not the body handles high-fructose corn syrup differently than table sugar.” “We do know, however, that too much added sugar — not just high-fructose corn syrup — can contribute unwanted calories that are linked to health problems, such as weight gain, type 2 diabetes, metabolic syndrome and high triglyceride levels,” Ms. Nelson wrote.
“The American Heart Association recommends that women get no more than 100 calories a day from added sugar from any source, and that most men get no more than 150 calories a day from added sugar. That’s about 6 teaspoons of added sugar for women and 9 teaspoons for men,” Ms. Nelson noted. “If you’re concerned about your health, the smart play is to cut back on added sugar, regardless of the type,” she advised.
The U.S. Food and Drug Administration (FDA) notes that it receives many inquiries about the safety of consuming high fructose corn syrup. The FDA states on its website, “FDA receives many inquiries asking about the safety of HFCS [high fructose corn syrup], often referring to studies about how humans metabolize fructose or fructose-containing sweeteners. These studies are based on the observation that there are some differences between how we metabolize fructose and other simple sugars.”
The official position of the FDA at this time remains: “We are not aware of any evidence, including the studies mentioned above, that there is a difference in safety between foods containing HFCS 42 or HFCS 55 and foods containing similar amounts of other nutritive sweeteners with approximately equal glucose and fructose content, such as sucrose, honey, or other traditional sweeteners.”
However, the FDA advises, “The 2010 Dietary Guidelines for Americans recommend that everyone limit consumption of all added sugars, including HFCS [high fructose corn syrup] and sucrose. FDA participated in the development of the Dietary Guidelines and fully supports this recommendation.” For more information about the 2010 Dietary Guidelines for Americans, see “New Dietary Guidelines for Americans Issued by USDA and HHS.”
It should be noted that the processed food industry has mounted a well-financed campaign to promote the idea that high fructose corn syrup is a safe food and not necessarily linked to obesity. This campaign is being waged through such organizations as the International Food Information Council, which is funded by for-profit companies including Coca Cola, The Dannon Company, Inc., General Mills, Inc., Kraft Foods, and Mars, Incorporated, some of whom also have appointed Trustees serving on the Board of Trustees of the organization. This organization has funded studies concluding that high fructose corn syrup is safe and questioning other studies linking it to obesity, and has published a glossy brochure Fast Facts About High Fructose Corn Syrup (PDF), alleging that high fructose corn syrup is safe, contains no more calories than table sugar, and that “HFCS, table sugar, and honey all are digested and metabolized similarly.”
Which Foods are High in Fructose?
According to Livestrong, processed foods high in fructose include “Ketchup and condiments, soups, sweet pickles, frozen foods, boxed breakfast cereals, canned foods, boxed dinners, breads and crackers,” “commercially-prepared baked goods such as cakes, brownies, pies, energy bars, cookies, croissants and doughnuts,” as well as “caffeinated and decaffeinated carbonated beverages of all flavors, [such as] [p]ops, soft drinks and white drinks, and fruit drinks.”
See also a list of Foods Highest in Fructose, published by Self Nutrition Data.
The full report of the new Yale study, “Effects of Fructose vs Glucose on Regional Cerebral Blood Flow in Brain Regions Involved With Appetite and Reward Pathways,” is available online in the January 2, 2013 issue of JAMA, the journal of the American Medical Association.
See related HelpingYouCare® reports on:
See also, The Common Food Ingredient That’s Making You Stupid, an article published by Rodale, discussing a recent UCLA study measuring the health effects on your brain of consuming a diet high in high fructose corn syrup.
For more information about the obesity epidemic and on weight loss and how to maintain a healthy weight, see the HelpingYouCare® resource page on:
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