How a Sugar High Works in the Brain

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High glycemic levels of food triggers the reward and craving center of the brain

June 26, 2013 / Author:  / Reviewed by: Robert Carlson, M.D Beth Bolt, RPh

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(dailyRx News) Is food addiction real? A candy bar can’t exactly be compared to heroin, but the sugar spike from candy may wake up the same part of the brain that substance abuse can trigger.

In a small clinical trial, a group of obese men had brain scans after eating high-carb and low-carb meals.

After eating the high-carb meal, the men experienced blood sugar spikes, cravings and an increased blood flow in the area of the brain associated with reward.

"Eat a healthy diet with lots of vegetables."

David Ludwig, MD, PhD, director of New Balance Foundation Obesity Prevention Center at Boston Children’s Hospital, worked with a team of scientists to investigate the concept of food addiction.

Different foods affect the body’s glucose levels in the blood, or blood sugar, in different ways. Foods rank from low to high on the glycemic index scale, which ranges from 0 to 100 based on how the body digests the food.

For example, candy, white rice, potatoes, white bread and soda drinks all rank very high on the glycemic index scale because they trigger a spike in a person’s blood sugar and, in turn, are digested very quickly.  These types of food are often called simple carbs.

On the other hand, low glycemic foods, like beans, nuts, olive oil and many kinds of vegetables, are digested more slowly, keeping blood sugar at a more even level. These foods are often called complex carbs.

For this small clinical trial, 12 otherwise healthy overweight or obese men, between 18 and 35 years of age, were given functional magnetic resonance imaging (fMRI) brain scans during the four-hour period after eating two different types of meals.

The brain scans were done once after the men had eaten a high glycemic meal, and again, between two to eight weeks later, after eating a low glycemic meal. Both the low and high glycemic meals were in the form of a milkshake, which contained the same number of calories (500 total) and were designed to be very similar in taste, look and smell.

The brain scans showed an increased blood flow in the area of the brain involved with cravings and reward after participants ate the high glycemic meal compared to the low glycemic meal.

Previous studies have shown that blood flow increases in this same reward area of the brain after a person consumes drugs, alcohol or tobacco.

"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," Dr. Ludwig said in a press release.

The researchers concluded that eating a meal with a high glycemic index, compared to a meal with a low glycemic index, increased activity in brain regions related to hunger, reward and craving after eating a meal, which could influence cravings for the next meal.

These researchers recommended further study into the concept of food addiction and underlying mechanisms.

"The study by Ludwig et al is an interesting finding that is unfortunately firmly entrenched in the land of calorie counting, but does weigh in on the reality of food cravings," Deborah Gordon, MD, told dailyRx.

"Clearly, high glycemic load of the entire meal, not just the glycemic index of individual foods, results in what has been called sugar swings, or Sugar Blues, famously described in William Duffy's 1975 classic book of the same name. Sugar swings stimulate appetite, and lower glycemic index foods provoke less of an insulin response," said Dr. Gordon, who was not involved in this study.

"It's not just the food generating the insulin response, however, it's also the individual's tendency to insulin resistance, which was probably a strong tendency in this group," she continued.

"Insulin resistance is certainly a part of the described dynamic, allowing blood sugar to remain high until larger and larger amounts of insulin are secreted, resulting in a precipitous sugar drop and food cravings," she explained.

"Insulin resistance, abdominal obesity, and inflammation are the tough obstacles in reversing obesity, and usually require a more comprehensive dietary shift than changing glycemic index," she said.

"What I would like to see is a highly palatable (brain stimulating!) menu that decreases insulin resistance. Such a plate would include well-raised meat, vegetables, healthy fats (bacon, avocados, nuts), and would be both satiating and highly pleasing. Oh, and it would have a low glycemic index as well!" Dr. Gordon said.

This study was published in June in the American Journal of Clinical Nutrition.

The National Institute of Diabetes and Digestive and Kidney Diseases, the National Institute of Mental Health, the National Center for Research Resources, the Pediatric Endocrine Society, the Endocrine Fellows Foundation and the New Balance Foundation provided funding for this study. GE Healthcare resources also were used in this study. GE Healthcare is a MRI vendor.