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    Ideas | Kelly Kasulis

    How breakfast rewires your brain

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    The traditional American breakfast is a high-carb affair, with its heaping dishes of pancakes, waffles, toast, cereal. It may affect not just our waistlines, but also who we are.

    In a recent study at the University of Lübeck in Germany, scientists asked participants about what they ate in the morning, then had them play the “ultimatum game” — a common experiment that measures how much people tolerate unfairness. In essence, they were trying to test whether human behavior is subject to a well-known cliché: Are we what we eat?

    “We wanted to know whether our decision-making or thoughts might depend on what we’ve eaten,” said So Young Park, a professor of social psychology and neuroscience at the University of Lübeck. “We eat three times a day. And you can imagine that, if we change our behavior depending on our food, that would be quite striking information.”

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    The ultimatum game puts study participants in an uncomfortable scenario. Players A and B are told that there is $10, but Player A must decide how the money is split between them. Scientists asked their study participants to act as Player B and watched how they reacted to lopsidedly unfair offers, such as being offered $1 out of $10. Study participants were told that, if they decided to reject an offer, neither person would take home any money at all.

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    In theory, “the respondent should accept any offer greater than zero, no matter how small, because it’s better than nothing,” said Tobias Kalenscher, a professor of comparative psychology at the University of Düsseldorf. “But respondents often would rather have nothing than live with an unfair deal.”

    Though even a $2 offer could mean a nice doughnut for the next morning, scientists found that participants with high-carb breakfasts rejected unfair offers 40 percent more often than those with high-protein breakfasts.

    “We could see a very tremendous difference in these people,” Park said. In a second experiment, breakfast was fed directly to study participants before they played the ultimatum game. Scientists found similar results, as well as differences in participants’ blood samples.

    “High-carb people had lower tyrosine levels. And the lower the tyrosine levels, the higher the rejection rate,” Kalenscher explained. Tyrosine is an amino acid that acts as a precursor for dopamine, a neurotransmitter that plays a significant role in our brain’s reward system. But this connection doesn’t mean that we should clear out our cupboards and start anew with high-protein, low-carb diets.

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    “You can say that people with high rejection rates are just sensitive to unfair treatment,” Kalenscher said. “It’s absolutely not a bad thing.”

    The point is that “food dictates your choices,” Park said. “Depending on what you have eaten, your choice is being dramatically modulated — that is what we’re showing. You should really try to have a balanced diet.”

    Kelly Kasulis is a freelance journalist. Follow her on Twitter: @KasulisK.