The ability to fight food cravings may lie in the head, according to a new study published in the Journal of Clinical Investigation.
By manipulating blood sugar levels in study participants and monitoring their brains with functional MRI scanners, researchers from Yale University and the University of Southern California found that obese people had a more difficult time fighting off cravings for high-calorie foods, which could explain why it is difficult for obese people to lose weight.
The researchers showed five obese and nine nonobese study participants pictures of high-calorie foods (including French fries and doughnuts) low-calorie foods (including tofu and salads) and nonfoods. When blood sugar levels were low in both obese and nonobese participants, the region of the brain associated with reward was activated, triggering a desire to eat high-calorie foods. Once the levels were brought back up to normal in the nonobese group, there was increased activity in the prefrontal cortex, the region of the brain involved in impulse control. The nonobese people were then less interested in the high-calorie foods.
This was not the case for obese participants. Not only was the desire for high-calorie foods more noticeable in their brain activity, when their blood sugar levels were brought back up to normal, their brains continued to show a craving for high-calorie foods.
"This is significant for the obesity epidemic, as it shows for the first time that obese individuals may have a particularly hard time restraining themselves when faced with high calorie foods and food cues in the environment, and that they are at greater risk for giving in and consuming high-calorie foods," said Rajita Sinha, co-author of the study and professor of psychiatry at the Yale Child Study Center.
Dr. Robert Sherwin, co-author of the study, said that these findings show that there are biological factors that influence how people control food cravings.
"My advice to people trying to lose weight is to eat frequent, small healthy meals and small snacks so that glucose doesn't significantly drop," said Sherwin. "If you wait until after lunch to have your first meal, your blood sugar is gong to drop so much that it's going to drive you to keep eating."
Blood glucose is the primary source of energy with in the body's cells. While blood sugar levels fluctuate throughout the day, low blood sugar levels can cause sleepiness and impaired cognitive function.
Dr. David Katz, director of the Yale Prevention Center, said that appetite and hunger are fundamentally about survival and therefore cause a hardwired brain response.
"That calories beckon when blood sugar falls makes sense for us all," said Katz. "Our native responses are often misguided in a world of highly processed, hyperplatable, energy-dense foods, to insulin resistance and metabolic syndrome."
About one-third of American adults are obese, according to the Centers for Disease Control and Prevention. As obesity continues to plague the U.S. and the rest of the world, experts say the study's findings could help in how obesity is treated in individuals.
"This is important information for anyone trying to lose weight," said Dr. Jana Klauer, a New York City physician who specializes in weight control and nutrition. "If you're trying to lose weight, keep a healthy snack with you, like a piece of fruit or a handful of nuts. At meals, try to include lean protein because it is digested slowly, allowing you to stay satisfied longer."