Does Sugar Make Your Heart Sweeter?

By Rita Rubin
WebMD Health News

Reviewed by Brunilda Nazario, MD

April 14, 2014 -- Celebrity Snickers pitchmen Joe Pesci and Don Rickles show that "You're not you when you're hungry."

In a Snickers commercial, Pesci and Rickles make rude comments to strangers they meet at a party. Now a new study suggests that the commercial might have a hint of truth: Hunger really may lead to greater aggression.

In the study, though, the aggression was directed not toward strangers, but toward someone much closer -- your spouse.

The researchers found that lower blood glucose levels predicted more aggression toward spouses, although some psychologists are skeptical of that theory.

Glucose is the sugar in your blood that your body uses for fuel.

"Numerous studies have found a relationship between low glucose levels and poor self-control," the researchers write in the Proceedings of the National Academy of Sciences. "When glucose levels are low, people have more difficulty controlling their attention, regulating their emotions, and overriding their aggressive impulses. Some evidence suggests that low glucose levels might even increase the risk of violent criminal behavior, including spousal abuse."

Hunger and Anger

The study involved 107 married heterosexual couples. They measured their blood glucose levels with a monitor twice daily for 3 weeks, before breakfast and before bedtime.

This is where the study gets a little unusual: Besides a glucose monitor, participants received a voodoo doll and 51 pins. The doll was supposed to represent their spouse. Every evening, in private, the participants stuck pins in the doll. How many depended on how angry they felt toward their spouse.

Voodoo dolls might seem like an unusual research tool, but study researcher Brad Bushman, PhD, says an earlier study by one of his collaborators showed the worth of their use.

At the end of the 3 weeks, the couples came back into the lab, where they were told they were going to play a computer game against their spouse. The goal: Be the first one to press a button after a square on the screen turned red. The winner would then get to blast the loser with loud noise through headphones. The noise was a mixture of irritating sounds, such as fingernails scratching a chalkboard and dentist drills. The winners got to pick the noise level and duration. If they were feeling warm and fuzzy about their spouse, they could choose silence instead of noise.

The couples didn't know that the researchers had rigged the game so everyone would have the same experience. The couples actually played against a computer, not each other, and everyone lost 12 out of 25 times. Also, the computer set the noise levels and length, no matter what the winners ordered.

The researchers found a link between daily blood glucose levels, the number of pins people stuck in their voodoo dolls, and the intensity of the noise with which they wanted to blast their spouse. The lower their glucose level, the more pins they used and the louder and longer they set the noise.

It's common sense that people are quicker to get angry when their blood sugar is low because they're hungry, says University of Pennsylvania psychologist Robert Kurzban, PhD.

"The fact that humans act differently when they're hungry is so well-known that Madison Avenue knows this," Kurzban says, referring to the Snickers commercial with Pesci and Rickles. "When you're really hungry, all you can do is think about food."

But in several blog posts and a journal article, Kurzban has questioned the popular theory that self-control is fueled by blood glucose levels. He cites a recent study that found drinking a sugary beverage did not improve performance on a task requiring self-control.

Still, few people would probably challenge Bushman's advice for married couples: "They should discuss sensitive topics over dinner, or, better yet, after dinner."


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SOURCES: Brad Bushman, PhD, Ohio State University. Proceedings of the National Academy of Sciences. Robert Kurzban, PhD, University of Pennsylvania. Kurzban, R. Evolutionary Psychology, 2010. The Evolutionary Psychology Blog. Lange, F. Appetite, April 2014.

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