Many fast for different reasons. Those who do so may be on guard, for they might find it difficult to resist high-calorie food on breaking the fast.
Low blood sugar influences the body's ability to resist, especially in obese individuals, according to research conducted by Keck School of Medicine of USC and Yale University faculty.
The study conducted by Kathleen Page, assistant professor of medicine in the Keck School's Division of Endocrinology while at Yale University, indicated that the area of the brain regulating impulsive behavior is less able to fight temptation for a big slice of pizza or a box of chocolate chip cookies when blood glucose is low. Glucose is the brain's primary fuel source.
Page is one of the lead authors of the study, which will is published online in The Journal of Clinical Investigation
"We've all experienced it - we skip breakfast, we're starving at lunch and the first thing we usually find to eat is unhealthy," Page said. "We know that a drop in blood sugar drives people to eat, but we didn't know the relationship of how the brain responds to low blood sugar and the foods we desire."
Page's team studied lean and obese individuals whose blood sugar had been reduced intravenously with insulin. Using functional magnetic resonance imaging, the researchers looked at which areas of the brain were activated when the test subjects viewed pictures of different kinds of foods, from fatty foods like cake and ice cream to more healthy choices such as salads and fruit. The subjects rated their desire for the foods.
All the test subjects desired the higher-calorie foods more when glucose levels dropped below normal. The brains of obese people in particular showed a lack of inhibition of impulsive desire for food.
"The prefrontal cortex is the part of the brain that says 'Stop eating,' " Page said. "When blood sugar levels are low, that area of the brain is less activated. Obese individuals lacked prefrontal brain activation even when sugar levels were normal. We don't know if obesity changes the way the brain responds or if it responds this way because of obesity."
Though more research is needed to determine reasons that obese people's brains respond differently to low blood sugar, the message for most people is: Give the brain a steady supply of fuel to prevent overeating.
"Eating healthy food that maintains glucose levels is the key," Page said.
The research was funded by the National Institutes of Health.