MONDAY, Sept. 19, 2011 (HealthDay News) -- A new study links low blood sugar in obese people to a greater desire within the brain for high-calorie foods, a finding that offers insight into why people who become overweight tend to stay that way.
"Their brains may be driving them to eat more and desire these foods more, and that may promote overeating," explained study author Kathleen A. Page. "We don't know if that's a consequence of obesity or contributes to the obese state. Are their brains wired differently from the start? Or does that happen after they become obese?"
Whatever the case, the research points to the importance of keeping blood sugar levels stable, said Page, an assistant professor of medicine at the University of Southern California.
Levels of sugar in the blood are directly linked to energy, and those levels often drop after eating lunch and cause a mid-afternoon slump. Blood sugar levels also drop in the morning, and after you eat a high-sugar food, Page said. In that case, the body's processing of the excess sugar can cause levels to dip.
In the new study, published in the Sept. 19 online issue of The Journal of Clinical Investigation, Page and colleagues tried to figure out if dips in blood sugar affect obese people differently than those who aren't overweight.
In the study, functional MRI scanners monitored the brains of five obese and nine non-obese people as researchers adjusted the levels of sugar in their blood, changing them from normal to low. At the same time, the researchers showed them pictures of foods that are low-calorie (various fruits and vegetables, tofu, soybeans, salads) and high-calorie foods (brownies, donuts, fried chicken, steak, ice cream and more).
The researchers found that the obese people had less brain activity in the area known as the prefrontal cortex, where powers of inhibition (choosing not to do things) are based, even when their blood sugar levels were normal. "That implies that obese people may have a harder time fighting off the urge to eat, especially when their sugar levels are below normal," Page said.
Jean-Philippe Chaput, an assistant professor at the University of Ottawa's School of Human Kinetics, said the research is relevant because it provides greater understanding into how blood sugar affects eating habits. "Future obesity treatments will need to take that aspect into account if we want to improve our chances of success," Chaput said.
But Dr. Marc-Andre Cornier, an associate professor of medicine at the University of Colorado, cautioned that the study doesn't definitively link blood sugar to hunger. "The lower glucose may have impacted another factor that in turn was responsible for the effects," he said, adding that it's "pure speculation" to say that keeping blood sugar levels stable after meals will reduce hunger.
For more about obesity, try the U.S. National Library of Medicine.