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How Your Brain May Be Making You Fat

Our daily stresses and mental fallacies make fighting obesity an uphill battle.

The following is an excerpt from Deborah A. Cohen's new book, A Big Fat Crisis: The Hidden Forces Behind the Obesity Epidemic—And How We Can End It ( Nation Books, a member of Perseus Books Group, 2013).

The limits of self-control are key factors in our poor eating habits. One reason self-control is limited is because the capacity of the brain’s information-processing system is relatively minuscule.

Scientists generally agree that our brain has two operating systems: a cognitive system and a noncognitive system. The cognitive system requires conscious awareness; it is reflective and deliberate. It can perform mathematical computations, make novel decisions, and engage in long-term planning and “out-of-the-box” thinking. It operates, on average, less than 5 percent of the time and is the internal resource responsible for self-control.

The other 95 percent of the time, our noncognitive system is in control. Impulsive and immediate—and following well-established rules and patterns—it is responsible for quick, automatic decision-making. The noncognitive system is often emotionally charged and responds to external signals, cues, information, signs, or symbols. When a person is under stress, tired, preoccupied, or overwhelmed with too much information, noncognitive processing dominates over thoughtful decision-making. Put more simply, when we are overloaded, we tend to make decisions impulsively. And when it comes to food, impulsivity typically leads to nutritionally poor choices and what we perceive as a loss of self-control.

We can think of our brain as being engaged in a constant ebb and flow between deliberate and automatic processing. Sometimes it is more of a fight between two mismatched warriors, like David and Goliath. David represents the small, nimble, and smart cognitive force that has to face a massive, primitive, noncognitive giant that is in charge most of the time. Goliath is unflagging and never sleeps. Sometimes David can win, but it is nearly impossible for him to win all the time. David can be distracted, he can be worn down, and he needs to sleep. This is not a single battle but an eternal struggle.

Limited Processing Capacity and Food Choices

To illustrate how the cognitive and noncognitive systems interrelate, psychologists Baba Shiv and Alexander Fedorikhin developed an experiment that looked at the kind of decisions people make when their cognitive systems are occupied (also called a “cognitive load”), compared to when they have less to think about. In this study 165 participants were asked to memorize either a two- or seven-digit number (the same length as a phone number without the area code). After they were shown the number briefly on an index card, they were asked to memorize it and then select a ticket for a snack, which was supposed to be a token reward for participating in the study. The participants got to choose either a piece of chocolate cake or a fruit salad. After they selected the ticket, they had to disclose the number they memorized and then complete a final questionnaire about the factors that influenced their choice of snack. Presented with the sentence “My final decision about which snack to choose was driven by . . .” they were asked to choose between “my thoughts or feelings,” “my willpower or desire,” “my prudent self or my impulsive self,” “the rational side or the emotional side,” and “my head or my heart.”

Among participants who had to memorize the two-digit number, 41 percent chose the chocolate cake, while among those who memorized the seven-digit number, 63 percent chose chocolate cake, a 50 percent difference. Those who had to memorize the seven-digit number said their decision was influenced more by their emotional, impulsive side than by their rational, prudent side. The researchers concluded that the group memorizing the longer number had less available brainpower to carefully consider the items, and resorted to impulse.

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