Consumption of a meal that has a high glycemic index (GI) appears to stimulate key brain regions related to craving and reward, a finding that supports the controversial hypothesis of food addiction, new research suggests.
Investigators from Boston Children's Hospital in Massachusetts found that compared with consumption of a low-GI meal, a meal high in refined carbohydrates decreased plasma glucose, increased hunger, and selectively stimulated brain regions 4 hours after eating — a critical time point that influences eating behavior at the next meal.
"We think we have shown for the first time that refined carbohydrates' biological effects can provoke, independent of calories and tastiness, symptoms related to addiction in susceptible people — those who are overweight or obese," said the study's principal investigator, David Ludwig, MD, from Boston Children's Hospital.
Dr. Ludwig, director of the hospital's New Balance Foundation Obesity Prevention Center, told Medscape Medical News that his team's preliminary findings support "the notion of food addiction [which] is very controversial because, unlike drugs of addiction, we have to eat to survive."
Craving Carbs
He said the randomized, blinded, crossover study in 12 overweight or obese men had several strengths over previous studies whose findings also suggested that certain tasty foods might be addictive.
"Prior studies, best described as observational, tended to compare vastly different foods, such as cheesecake and boiled vegetables," he said.
In the new study, participants aged 18 to 35 years consumed, in a randomized order on test days 2 to 8 weeks apart, 2 test milkshakes that had similar ingredients, calories (500 kcal), appearance, taste, and smell.
Participants were not aware which was the low-GI meal (37%) with slow-acting carbohydrate and which was the high-GI meal (84%) with fast-acting carbohydrate, and they reported no preference for either meal.
Additionally, the investigators monitored participants 4 hours after the meal, when the individuals likely would be considering what to eat at their next meal. At that time, participants underwent a final blood glucose test and neuroimaging, and rated their hunger levels.
After eating the high-GI meal, participants initially had a surge in blood glucose level that was 2.4-fold higher than after the low-GI meal, followed by a crash in blood glucose at 4 hours, the authors reported. They also reported excessive hunger 4 hours after the high-GI meal, Dr. Ludwig said.
Table. Effect of Low- vs High-Glycemic Index Meal on Patient Outcomes 4 Hours Later (n = 12)
| Outcome (mean ± standard error) | Low Glycemic Index | High Glycemic Index | P-Value |
| Hunger rating, change from baseline, cm | -0.01 ± 0.92 | 1.65 ± 0.79 | .04 |
| Venous plasma blood glucose, mmol/L | 5.30 ± 0.16 | 4.70 ± 0.14 | .005 |
The investigators looked directly at participants' cerebral blood flow, as a measure of resting brain activity, using arterial spin labeling functional magnetic resonance imaging (fMRI), which allowed them to examine persistent effects of test meals.
Results showed an 8.2% relative difference in cerebral blood flow between the high- and low-GI meals at 4 hours (mean difference, 4.4 ± 0.56 mL ∙ 100 g−1 ∙ min−1).
After correction for the prespecified anatomic regions of interest, Dr. Ludwig said that the difference was strongly significant (P = .0006), with "less than 1 in 1000 likelihood that the results were due to chance."
"Every single subject showed intense activation in the nucleus accumbens, the area of the brain related to addiction," he said.
The results show that highly processed carbohydrates, such as white bread, potatoes, and concentrated sugar, "alter brain activity in ways that make us crave them even more," he said.
Clear Take-Home Message
Dr. Ludwig stated that the study must be repeated in larger numbers of persons, in a more diverse population, and before and after weight gain. Yet he said that the initial results send a clear take-home message: "Avoiding highly processed carbohydrates could help overweight people avoid overeating."
Mark Gold, MD, a longtime researcher in the area of food and addiction, from the McKnight Brain Institute of the University of Florida (UF), Gainesville, said it is important that clinical research tests the food addiction hypothesis first generated by laboratory researchers.
Asked by Medscape Medical News to comment on the findings, Dr. Gold, who was not involved with the study, said that the brain imaging test the researchers used "is exceptional and provides additional strong evidence that manufactured foods, sugar, and fats can interact with the brain and systems that [also] are hijacked by drugs of abuse."
"Hedonic overeating...makes more sense with clinical research like this," Dr. Gold, who is professor and chair of psychiatry at UF College of Medicine, concluded.
This study was funded by the National Institutes of Health and the National Center for Research Resources, Bethesda, Maryland; the Pediatric Endocrine Society, McLean, Virginia; the Endocrine Fellows Foundation, Washington, DC; and the New Balance Foundation, Boston, Massachusetts. Dr. Ludwig and Dr. Gold have reported no relevant financial relationships.
Am J Clin Nutr. Published online June 26, 2013. Abstract
