How does fructose added to foods change your brain?

How does fructose added to foods change your brain? It makes you more hungry, and you tend to eat more. But when you eat sugar (or glucose) you feel less hunger and eat less food because you feel fuller sooner and don't want to keep on eating. But how the results of studies of fructose or sugar on feeding habits translate to humans is not yet fully understood by scientists.

When the human brain is exposed to fructose, you feel more hunger and eat more food. Scientists explain the process as fructose promotes increased food intake. In other words, the scientists report that "neurobiological pathways involved in appetite regulation are modulated, thereby promoting increased food intake."

A new study released today, January 1, 2013, "Imaging Study Examines Effect of Fructose on Brain Regions That Regulate Appetite," to be published tomorrow in the Journal of the American Medical Association (JAMA) and Archives Journals examines some of the possible factors regarding the associations between fructose consumption and weight gain. Brain magnetic resonance imaging (MRI) of study participants indicated that ingestion of glucose but not fructose reduced cerebral blood flow and activity in brain regions that regulate appetite. And ingestion of glucose but not fructose produced increased ratings of satiety and fullness, according to a preliminary study published in the January 2, 2013 issue of JAMA.

Sugar puts a lid on hunger, but fructose allows you to eat more without feeling full as fast

That means when you eat sugar/glucose in foods the blood flow to your brain is reduced and there's also a reduction of the activity in your brain related to feeling hungry. This brain change doesn't happen when you eat fructose.

Scientists reported, "Increases in fructose consumption have paralleled the increasing prevalence of obesity, and high-fructose diets are thought to promote weight gain and insulin resistance. Fructose ingestion produces smaller increases in circulating satiety hormones compared with glucose ingestion, and central administration of fructose provokes feeding in rodents, whereas centrally administered glucose promotes satiety," according to background information in the article, as explained in the January 1, 2013 news release, Imaging study examines effect of fructose on brain regions that regulate appetite. "Thus, fructose possibly increases food-seeking behavior and increases food intake."

How brain regions associated with fructose- and glucose-mediated changes in animal feeding behaviors translates to humans is not completely understood. Kathleen A. Page, M.D., of Yale University School of Medicine, New Haven, Conn., and colleagues conducted a study to examine neurophysiological factors that might underlie associations between fructose consumption and weight gain.

Blood flow circulation to your brain slows after you eat sugar/glucose

The study included 20 healthy adult volunteers who underwent two magnetic resonance imaging sessions in conjunction with fructose or glucose drink ingestion. The primary outcome measure for the study was the relative changes in hypothalamic (a region of the brain) regional cerebral blood flow (CBF) after glucose or fructose ingestion.

The researchers found, according to the news release, that there was a significantly greater reduction in hypothalamic CBF after glucose vs. fructose ingestion. "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."

"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." You can check out the original study or its abstract, "Fructose Ingestion and Cerebral, Metabolic, and Satiety Responses,"(JAMA. 2013;309(1):63-70.

Authors are Jonathan Q. Purnell, M.D., and Damien A. Fair, PA-C, Ph.D., of Oregon Health & Science University, Portland. They write in an accompanying editorial that, "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."

The supersizing concept and the nation's collective waistlines

The study also reports, "… the 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." Check out the original study published January 2, 2013 in JAMA, Imaging Study Examines Effect of Fructose on Brain Regions That Regulate Appetite.

Last year there also was a study done in Australia. Check out, What role does fructose have in weight gain? (Science Alert). That article has a link to numerous studies with rodents who were fed an excess amount of fructose such as high-fructose diets. The study also found that excess fructose consumption may lead to increased body weight, higher levels of blood lipids and higher blood pressure, and other components of metabolic syndrome (a condition that pre-disposes to several diseases, including heart disease and type 2 diabetes).

Is excess fructose addictive?

There’s also good evidence that fructose is addictive in rats, perhaps in a similar way to cocaine, according to the article, "What role does fructose have in weight gain? (Science Alert)." As a result, there’s speculation, that article reports, the fructose component of sugar may be one of the major driving forces behind the current epidemics of obesity and type 2 diabetes in humans. Studies continue.

The Science Alert article notes, "the proponent of this concept with the highest profile is a US professor of pediatrics, Dr Robert Lustig, who argues that fructose is “alcohol without the ‘buzz’”, that is, it’s addictive in people, toxic and equally harmful as alcohol." As studies continue, many people regard the findings as hypothesis, but then again, it depends upon how much fructose or sugar anyone actually consumes.

In Sacramento and Davis, the University of California scientists also study the impact of fructose on health

Excess fructose consumption raises your uric acid levels which in turn could raise your blood pressure. Check out the August 7, 2012 news release from the University of California, Davis, "Fructose consumption may impact development of metabolic syndrome." Prolonged fructose consumption may contribute to the development of metabolic syndrome, a combination of medical disorders that, when occurring together, increases the risk of developing cardiovascular disease and diabetes.

The findings, published in August 2012 online in the journal Nutrition & Metabolism, are derived from a UC Davis study that investigated the relative effects of fructose or glucose consumption on 32 older, overweight or obese men and women who consumed glucose- or fructose-sweetened beverages, which provided 25 percent of their energy requirements for 10 weeks. Scientists are concerned with looking at any relationship between metabolic syndrome and increased circulating uric acid. The idea is to eat foods that don't dramatically increase your amounts of uric acid.

Consumption of fructose, but not glucose, impacted various parameters associated with metabolic syndrome, including increased circulating concentrations of uric acid, which is known to be higher in people with metabolic syndrome, increased GGT activity, which is an indicator of liver dysfunction, and production of a type of protein known as RBP-4, associated with increased insulin resistance. No previous studies have investigated the effects of glucose or fructose consumption on circulating levels of RBP-4.

The study design involved three phases, including a two-week inpatient baseline period, an eight-week outpatient intervention period, and a two-week inpatient intervention period. During baseline, subjects resided in the UC Davis Clinical and Translational Science Center's Clinical Research Center (CCRC) for two weeks before beginning the outpatient intervention, consuming either fructose- or glucose-sweetened beverages. They returned to the CCRC for the final two weeks of intervention.

Fasting and 24-hour blood collections were performed at baseline and following 10 weeks of intervention for measurement of plasma concentrations of uric acid, RBP-4 and liver enzyme activities. The study's first results, published in 2009, showed that visceral adipose volume (fat inside the abdominal cavity) was significantly increased only in subjects consuming fructose, along with increases in several circulating lipids and a decrease in insulin sensitivity, although both groups exhibited similar weight gain.

Scientists at U.C. Davis in various studies compare the impact of glucose, fructose, and high fructose corn syrup on the health of younger patients

Senior author Peter Havel, a UC Davis professor with joint appointments in the Department of Molecular Biosciences in the School of Veterinary Medicine and the Department of Nutrition, is currently the principal investigator for a follow-up study comparing impacts of glucose, fructose and high-fructose corn syrup in younger patients. His colleague and collaborator, Kimber Stanhope, directed and coordinated the clinical research study.

Glucose and fructose are both simple sugars, and equal parts of each is the recipe for table sugar (sucrose). The pure glucose and fructose that were used to sweeten the beverages in this study are not found in nature. Most fruits and honey contain comparable amounts of glucose, fructose and sucrose. Grains such as wheat, oats, corn and barley contain large amounts of glucose (and negligible amounts of fructose), but the glucose is packaged as long chains that are called starch or complex carbohydrate.

Co-author Lars Berglund, director of the UC Davis Clinical and Translational Science Center, points out that fruit juices typically feature more concentrated forms of these sugars, while fruits and vegetable contain fiber and other beneficial components.

"It's healthier to eat apples than to drink apple juice," said Berglund, according to the U.C. Davis August 7, 2012 news release. Other authors include former graduate students Chad Cox, James Graham, Bonnie Hatcher, Steven Griffen and John McGahan, all of UC Davis; Jean Marc Schwarz of Touro University, Vallejo, Calif.; Andrew Bremer of Vanderbilt University, Nashville; and Nancy Keim of UC Davis and the U.S. Dept. of Agriculture, Davis, Calif.

The 2012 research at U.C. Davis was supported with funding from National Institutes of Health (RO1 HL-075675), the NIH's National Center for Research Resources (UL1 RR024146), and the NIH Roadmap for Medical Research. Havel's laboratory receives support from the NIH (HL-091333, DK-097307, and DK-095980) and a Multicampus Award (#142691) from the University of California, Office of the President, and Keim's research is supported by intramural U.S. Department of Agriculture-Agricultural Research Service (ARS) Current Research Information System (CRIS) grant 5306-51530-016-00D.

Also see, Upcoming events, including the distinguished lecturer series at U.C. Davis. And check out the related studies on high-fructose diets such as the following: A 4-week high-fructose diet alters lipid metabolism without affecting insulin sensitivity or ectopic lipids in healthy humans. [Am J Clin Nutr. 2006] . You also may want to see another study, "Being Overweight Appears Associated With Slightly Lower All-Cause Mortality Relative To Normal Weight."

Resources on health and nutrition

Resources for studies on fructose, appetite regulation, and any brain or liver changes