NUTRITION
July 10, 2013

Addicted to Carbs

High glycemic foods like soda and refined flour light up an area of the brain much the way drugs do.

You may have experienced the hunger that a high-carb meal can bring, but you may not be aware it can be a sign of addiction. Eat a huge bagel for breakfast and you may find you are hungrier at lunchtime than if you had eaten a small bowl of oatmeal and an egg. Now we understand why this happens.

Eating refined carbohydrates — like bagels or muffins — causes your blood sugar levels to skyrocket, and then nose-dive four hours later, about the time you are considering your next meal. If that next meal also contains refined carbohydrates, you may be setting yourself up for cravings, much like the cravings that drug addicts experience.

In some, refined carbohydrates can cause symptoms related to addiction. The researchers suspect that such a cycle may not only cause a disruption in the brain’s reward circuitry and increase our urge to eat more high-glycemic foods, but it may also disrupt our ability to control our impulse to do so.

The findings from the study conducted by researchers at Harvard Medical School and Boston Children’s Hospital suggest that the quick rise and fall of blood sugar that occurs after eating foods with a high glycemic index activates the part of the brain that is involved in emotions and addiction.

The glycemic index is an indication of how fast or slow a food causes a rise in blood sugar. When carbohydrates are eaten, they are broken down into glucose, or blood sugar. Sugar, corn syrup and white flour break down quickly and cause a rapid rise in blood sugar. Whole grains and the carbohydrates in fruits and vegetables break down more slowly and cause blood sugar levels to rise more gradually.

The researchers fed 12 overweight and obese young men two milkshakes. One was made with cornstarch, which has a low glycemic index, and the other contained corn syrup, which has a high glycemic index. Over the next few hours, the men’s blood was drawn to assess their metabolic response to the milkshakes, and they were asked to express their perceived degree of hunger.

After consuming the milkshake made with corn syrup, the men’s blood sugar levels spiked and then plummeted four hours later, at which time they reported feeling very hungry. MRI scans of the men’s brains at that time showed intense activation in the nucleus accumbens, a region of the brain associated with addictive behavior. As a result, the person craves more of the same high-glycemic food.

David Ludwig, MD, lead investigator of the research, said that this study may have shown for the first time that the biological effects of refined carbohydrates can cause symptoms related to addiction in susceptible people. The researchers suspect that such a cycle may not only cause a disruption in the brain’s reward circuitry and increase the drive to eat more high-glycemic foods, but it may also disrupt the ability to control the impulse to do so.

To put it simply, the findings from this research suggest that when we eat foods made with refined carbohydrates — white bread, pasta, or rice, cookies, doughnuts, or sugary cereals, for example — it makes us crave them even more.

Although this study was small and only looked at overweight and obese men, it is important. The men did not know what they were drinking, yet the physiological effects of consuming the high glycemic milkshake were clear.

The whole idea of food addiction is controversial, but one that merits further research in larger numbers of people, in a more diverse population, and before and after weight gain, according to Dr. Ludwig. In fact, he believes that the take-home message from this study is that overweight people could avoid overeating if they skipped highly processed carbohydrates.

The study is published in the American Journal of Clinical Nutrition.

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