Foods high on the glycemic index, such as highly processed carbohydrates found in white flour, can cause excess hunger and stimulate brain regions involved in reward and cravings, according to research conducted by a team at Boston Children's Hospital. These findings suggest that limiting high GI foods could help obese individuals avoid overeating.
The study, conducted by a team led by David Ludwig, MD, PhD, director of New Balance Foundation Obesity Prevention Center, was published in The American Journal of Clinical Nutrition on June 26, 2013. It investigates how food intake is regulated by dopamine-containing pleasure centers of the brain.
"Beyond reward and craving, this part of the brain is also linked to substance abuse and dependence, which raises the question as to whether certain foods might be addictive," Ludwig said.
Just the carbohydrate properties
While the notion that avoiding the high GI carbs found in white bread and French fries can help overeaters manage their weight is not new, this research is different because of its design, according to the study’s first author Belinda Lennerz, MD PhD.
“In a way it’s ground breaking. Research like this has never been done before. There are studies that look at brain activation in response to hunger and satiety or in response to looking at pictures of palatable food or fast food. But those studies all take into account the pleasure of the food,” Lennerz told FoodNavigator-USA.
Lennerz conducted the study while at Harvard University; she is now at the University of Ulm in Germany. The study design she came up with eliminates the associations and emotional attachments that subjects might have with different kinds of foods.
“So we are able to look for the first time at what the type of carb does to the brain, not what pleasure does to the brain. This is really reduced just to the food properties,” she said.
MRIs look at brain activity
To examine the link, researchers measured blood glucose levels and hunger, while also using functional magnetic resonance imaging (MRI) to observe brain activity during the crucial four-hour period after a meal, which influences eating behavior at the next meal. Evaluating patients in this time frame is one novel aspect of this study, whereas previous studies have evaluated patients with an MRI soon after eating.
Twelve overweight or obese men consumed test meals designed as milkshakes with the same calories, taste and sweetness. The two milkshakes were essentially the same; the only difference was that one contained rapidly digesting (high-glycemic index) carbohydrates in the form of corn syrup and lactose-free milk, and the other slowly digesting (low-glycemic index) carbohydrates. The meals were consumed on two occasions several weeks apart. The study was restricted to men to avoid the complicating factor of the menstrual cycle.
After participants consumed the high-glycemic index milkshake, they experienced an initial surge in blood sugar levels, followed by sharp crash four hours later.
Addiction center activated
This decrease in blood glucose was associated with excessive hunger and intense activation of the nucleus accumbens, a critical brain region involved in addictive behaviors.
“In a way the results support the notion that (the obesity crisis) is addiction related,” Lennerz said.
“If you look at the data there is a strong correlation between the rising obesity rates and the increase in the consumption of highly processed foods and soft drinks. This may just mean that either all of us or at least a subset of us is not equipped to deal with that environment,” she said.
Though the concept of food addiction remains provocative, the findings suggest that more interventional and observational studies be done. Additional research could help inform clinicians about the subjective experience of food addiction, and how they can potentially treat these patients and regulate their weight.
Published ahead of print June 26, 2013, doi: 10.3945/ajcn.113.064113
"Effects of dietary glycemic index on brain regions related to reward and craving in men"
Belinda S Lennerz, David C Alsop, Laura M Holsen, Emily Stern, Rafael Rojas, Cara B Ebbeling, Jill M Goldstein, and David S Ludwig