Fat vs. Sugar: Which Do We Crave More?

Scientists scan the brain for clues to obesity.

People have a stronger inborn preference for sugar than for fat, according to a new study.

In the drama of obesity in America, fat and sugar have been fingered as indisputable villains. But which prime suspect is more sinister?

Eric Stice, a senior researcher at the Oregon Research Institute, and his colleagues fed milkshakes to 106 high school students while they were undergoing functional magnetic resonance imaging (fMRI) to see how reward centers in the brain reacted to shakes that were tilted in favor of either fat content or sugar content. The study, funded by the National Institutes of Health and published in the American Journal of Clinical Nutrition, concluded that sugar was the more nefarious of the two. We asked him to elaborate.

Tell us what's new about your study.

We're one of the first labs to give people food while in a brain scanner. We applied imaging to the reward regions of the brain and were able to say that sugar is able to grab reward circuitry and drive compulsive intake more than fat.

You indicate that the more sugar you eat, the more you crave. It sounds like we are talking about addiction.

It's absolutely like drugs of abuse. I would have never bet money on this. I still remember discussions with my mother. "If you feel bad … eat chocolate."

"Oh, Mom," I'd say. But as often is true, mothers are right.

Could you quantify the obesity problem?

About 60 to 70 percent of the population in this country is overweight or obese. We lose 300,000 people a year to it. It's mind-boggling compared with the other things we worry about, like terrorism.

What are the practical applications of the study?

If I were the mayor of New York, I would definitely go after sugar versus fat.

Which New York Mayor Michael Bloomberg did, of course, when he banned large sugary drinks.

Yes, but it was then overturned. [In March, Justice Milton A. Tingling of State Supreme Court in Manhattan struck down Bloomberg's proposed law limiting large sugary drinks one day before it was to take effect.]

What's the basis for our sugar cravings?

It seems to be the case that we have a stronger inborn preference for sugar. In early times, we died from not having enough food. The preference makes sure you get enough calories. There is absolutely no brake on overconsumption.

Why did you choose high school kids for the study?

We chose high school kids because the study is seeking to capture the initial neurological vulnerability factors that increase risk for future weight gain and whether weight gain and overeating energy-dense foods causes changes in reward circuitry. So we wanted to study kids before they show unhealthy weight gain.

On the good side, isn't consumption of fat down?

In the 1970s, we discovered that fat caused all those heart attacks. So there was a big push to cut it down. We've done a better job of cutting out fat. But we are overeating more, and we have replaced fat with sugar. There is sugar in foods that never had it before, like ketchup or spaghetti sauce. The food industry is selling what people like to swallow.

Unhappily, it seems we are constantly sabotaged by our brain chemistry. What's the answer?

We promote a gradual retraining approach, a gradual decrease of sugar.

Is all sugar created equal?

Carbohydrates include simple carbs—sugar—and complex carbs like fruit and whole grains. Simple carbs come in a lot of varieties, including sucrose, glucose, and high-fructose corn syrup. Even vegetables like carrots are high in sugar. So if you get 60 percent of your carbs from fruits and vegetables, that's great, because they deliver fiber—which makes us feel full—and vitamins and minerals. Simple sugars like soda, however, just give us calories, with no nutrient benefits.

What did you eat for breakfast today?

Special K. I'm a cereal eater. My wife says it has too much sugar. But I don't drink sodas.

(Read "Sugar" in National Geographic magazine.)