Consuming fructose appears to cause changes in the brain that may lead to overeating, a new study suggests.
"Increases in fructose consumption have paralleled the increasing prevalence of obesity, and high-fructose diets are thought to promote weight gain and insulin resistance," lead author Kathleen A. Page, MD, and colleagues from Yale University in New Haven, Connecticut, write.
In this study, they showed in healthy volunteers that although glucose ingestion resulted in reduced activation of the hypothalamus, insula, and striatum on MRI — areas that regulate appetite, motivation, and reward processing — as well as increased functional connections between the hypothalamic striatal network and increased satiety. Fructose ingestion had none of these effects.
"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," they conclude.
Their findings are published in the January 2 issue of the Journal of the American Medical Association.
Glucose vs Fructose
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, the authors write. "Thus, fructose possibly increases food-seeking behavior and increases food intake."
In this study, the researchers used arterial spin labeling MRI to quantify regional cerebral blood flow in 20 healthy normal-weight adult volunteers before and after drinking a 75-g beverage of pure glucose or fructose.
They observed that glucose (but not fructose) ingestion reduced activation of the hypothalamus, insula, and striatum. Glucose ingestion also increased functional connections between the hypothalamic-striatal network and increased ratings of satiety and fullness.
Brain responses were markedly different after ingestion of an equal amount of fructose. Not only did fructose fail to diminish hypothalamic activity, but it also induced a small, transient increase in hypothalamic activity.
The striatum, as with the hypothalamus, also did not deactivate with fructose ingestion, which may cause decreased inhibitory responses. Fructose ingestion was also associated with reduced systemic levels of the satiety-signaling hormone insulin.
"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," Jonathan Q. Purnell, MD, and Damien A. Fair, PhD, from Oregon Health & Science University, Portland, write in an accompanying editorial.
They say the implications of this study, coupled with 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."
The study was supported in part by grants from the National Institutes of Health and the Yale Center for Clinical Investigation. The authors and editorialists have disclosed no relevant financial relationships.
Fructose Makes You Fat And Unhealthy04 April 2010 By: Bryan Marcel, Certified Personal Trainer .
Fructose is a sugar that occurs naturally in fruits, vegetables and honey. In its whole food form fructose is healthy in moderation. From 1967 to 2007 the amount of fructose consumed in its natural form (whole fruit, vegetables and honey) has remained constant . The problem occurs when the fructose is removed from its source and added to processed foods and drinks. For this article when I refer to fructose it will be in the context of this “free” fructose, fructose that has been removed from its natural source, such as fruit juice.
Free fructose is processed by the body very differently from intact fructose. Over the last 30 years our intake of fructose as a sweetener has grown from 0 in 1967 to 63.93 pounds per person per year today primarily in the form of high fructose corn syrup (HFCS) and sucrose (50% fructose). This amounts to about 318 calories per day. It isn’t the 318 calories that matter.
What matters is the form that those calories are in and how your body will process them. 318 calories of HFCS will not process the same way in your body as 318 calories of whole fruits and vegetables.
Added sugars (sugar, syrup, anything that ends in “…ose” sucrose, fructose, lactose, maltose, dextrose, etc) have become part of almost all processed foods and drinks. In 1977 HFCS-55, a high fructose corn syrup with 55% fructose came to market. The development of this inexpensive and profitable corn-based syrup now represents 40% of all added sweeteners to foods. The main push came from the soda industry. The United States uses more HFCS than any other country in the world.
Most sugars such as sucrose are processed in the small intestine. Fructose is unique in that it is transported to the liver where it is either processed into glucose (what our bodies convert all food into for energy) or it is passes into blood circulation. But unlike sugar, fructose does not stimulate a large insulin response by the pancreas. Insulin stores excess sugars as fat and increases leptin production. Leptin is a protein consisting of 167 amino acids that have a key role in regulating appetite and metabolism. Simply put, the more leptin your body produces the less you eat.
So, since fructose doesn’t stimulate a lot of insulin production, leptin isn’t as readily produced and you are prone to eat more than what your body needs. A good example of that is a person who’s body doesn’t produce leptin at all. That person will be extremely obese since they have no way of regulating their appetite. Also unlike sugar, fructose is not transported to the brain, so the brain not seeing the fructose, fails to get a “satiety” signal. The satiety signal would have told you that you were full so you would stop eating. Fructose basically “tricks” you into overeating. A University of Florida Gainsville study showed that consumption of fructose resulted in weight gain, gout (a painful form of arthritis), elevated triglyceride levels (a very common condition in the U.S., the largest user of high fructose corn syrup) and elevated insulin levels .
It gets even more interesting when you consider a 2000 Purdue study on humans that showed that people who consumed carbohydrates in liquid form (soda, juice, etc) gained “significantly” more weight than those who consumed the same amount of carbohydrates in solid food form . This is because liquid fructose is processed differently than fructose in food. Either way, notice that both groups gained weight.
The only solution to this is to eliminate foods and drinks that contain added free fructose. Read the ingredient labels of all foods that you buy. If you see the word “fructose” anywhere on the label, don’t buy it. Remember that whole foods: meats, raw vegetables, eggs, whole fruits and whole foods don’t need an ingredient label.
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