Brain image study shows fructose may spur overeating
Tuesday, January 8, 2013
Scientists have used imaging tests to show for the first time that fructose, a sugar that saturates the American diet, can trigger brain changes that may lead to overeating.
After drinking a fructose beverage, the brain doesn't register the feeling of being full as it does when simple glucose is consumed, researchers found.
It's a small study and does not prove that fructose or its relative, high-fructose corn syrup, can cause obesity, but experts said it adds evidence they may play a role. These sugars often are added to processed foods and beverages, and consumption has risen dramatically since the 1970s along with obesity. A third of U.S. children and teens and more than two-thirds of adults are obese or overweight.
All sugars are not equal -- even though they contain the same amount of calories -- because they are metabolized differently. Table sugar is sucrose, which is half fructose, half glucose. High-fructose corn syrup is 55 percent fructose and 45 percent glucose. Some nutrition experts say this sweetener may pose special risks, but others reject that claim.
For the study, scientists used magnetic resonance imaging, or MRI, scans to track blood flow in the brain in 20 young, normal-weight people before and after they had drinks containing glucose or fructose in two sessions several weeks apart.
Scans showed that drinking glucose "turns off or suppresses the activity of areas of the brain that are critical for reward and desire for food," said one study leader, Yale University endocrinologist Dr. Robert Sherwin. With fructose, "we don't see those changes," he said. "As a result, the desire to eat continues -- it isn't turned off."
What's convincing, said Dr. Jonathan Purnell, an endocrinologist at Oregon Health & Science University, is that imaging results mirrored how hungry the people said they felt, as well as what earlier studies found in animals.
"It implies that fructose, at least with regards to promoting food intake and weight gain, is a bad actor compared to glucose," said Purnell. He wrote a commentary that appears with the federally funded study in Wednesday's Journal of the American Medical Association.
Researchers now are testing obese people to see if they react the same way to fructose and glucose as the normal-weight people in this study did.
What to do? Cook more at home and limit processed foods containing fructose and high-fructose corn syrup, Purnell suggested. "Try to avoid the sugar-sweetened beverages. It doesn't mean you can't ever have them," but control their size and how often they are consumed, he said.
Dr. Jimmy Bowen, a strength and conditioning specialist and sports medicine physician in Cape Girardeau, said use of alternative sweeteners should be limited.
Bowen recommends a few types of sweeteners that are healthier options, including coconut palm sugar or nector, green leaf stevia, honey and Grade B pure maple syrup.
Katherine Flegal of the Centers for Disease Control and Prevention defended her work. She noted that she used standard categories for weight classes. She said statistical adjustments were made for smokers, who were included to give a more real-world sample. She also said study participants were not in hospitals or hospices, making it unlikely that large numbers of sick people skewed the results.
"We still have to learn about obesity, including how best to measure it," Flegal's boss, CDC Director Dr. Thomas Frieden, said in a written statement. "However, it's clear that being obese is not healthy -- it increases the risk of diabetes, heart disease, cancer, and many other health problems. Small, sustainable increases in physical activity and improvements in nutrition can lead to significant health improvements."
Assistant managing editor Lucas Presson contributed to this story.
Local perspective with Dr. Jimmy Bowen, a strength and conditioning specialist and sports medicine physician who practices in Cape Girardeau.
Q: Do you agree with the study that fructose can lead to brain changes that may lead to overeating? Why or why not?
A: It is interesting that the increased use of fructose and high fructose products has paralleled the nations explosion of obesity and the diseases associated with obesity. The use of fructose in leu of glucose, and the use of artificial sweeteners in leu of "sugar" have been implicated in human and animal studies to influence the brains ability to appreciate having enough calories and to curtail intake of food. It is an interesting premise with some support from research. Unfortunately the research has primarily been short term and with few participants. Still remains a controversial subject. Obesity is much more complex and we can also point to changes in society, schools and priorities for activity that have lead to a nation that is less active overall.
Q: What's the difference between fructose and glucose? Why is glucose metabolized differently?
A: Fructose and glucose are both monosaccharides with the same chemical composition but a different molecular structure. These two sugars are found in some combination in nearly all sweetened foods available. Glucose needs insulin for proper metabolizing while fructose needs no insulin to be processed. Glucose is eaten, absorbed into the blood stream, and makes its way to the liver where it is broken down to supply energy to the entire body. This breaking down process requires insulin. Fructose is eaten and absorbed but releases its energy slower than glucose. It does not need insulin to be metabolized and therefore is a marginally better choice for a diabetic. Raw fructose is many times sweeter than glucose.
Q: What are some foods to avoid containing fructose or high-fructose corn syrup? What alternative foods do you recommend?
A: Avoid fast food. Read food labels. Understand what "natural" or "organic" means on labels with regard to HFCS; only foods labeled as 100 percent organic can be assumed to be HFCS-free. Avoid canned or bottled beverages. Soft drinks, sports drinks, lemonade, iced tea and almost every sweet drink you can think of contains high fructose corn syrup. Avoid processed foods.
4) What alternative sweeteners to you recommend instead of sugar?
Q: Should reduce the use of sweeteners altogether, as even many of the artificial sweeteners have been implicated as a cause of overeating. Consider: coconut palm sugar or nector, green leaf stevia, honey and Grade B pure maple syrup.