Why Is It So Hard to Stick to a Diet?

I know it’s risky. I’ve been drilled on the rule, and usually I’m pretty sensible about it. But every once in a while, if I’m feeling whimsical, I just do it: I go grocery shopping on an empty stomach.

It’s exhilarating. But I admit my behavior absolutely does change if I’m hungry—and the hungrier I am the more dramatic the changes. Those meal plans and lists organized by aisle? Forget them. Inspect the produce? What produce? I’m making a beeline for the high-fat side of the market, as if there were a medieval groaning board awaiting me at home. I’m stocking the larder for a brutal winter ahead.

And I don’t even use the word larder. So you see what I mean. The grocery rule has been recited since the days before bar codes, but this bit of folk wisdom is actually being validated today by a growing body of scientific research. Psychologists have been studying what they call the “empathy gap,” a common cognitive glitch that explains a lot more than that freezer full of frozen pizzas. Indeed, these psychologists are coming to believe that misunderstanding the body’s visceral drives—like hunger, thirst, fatigue and so forth—can undermine our well-being in serious and surprising ways.

The empathy gap refers to the fact that we’re not very good at gauging the importance of our fundamental urges—either in the future or when evaluating the past. The grocery shopping trip is a fairly harmless example: Because you’re hungry now, you “predict” that you will be just as hungry in the future, and buy accordingly. The same psychological dynamic can be seen in addicts, who genuinely believe they won’t be swayed by cravings yet are time and again. Or consider how much unsafe sex occurs in the heat of the moment, when cooler minds fail to emerge.

These are just anecdotes. But a team of psychologists at the University of Amsterdam, led by Loran Nordgren, has been examining similar drives, urges and cravings in the laboratory. Specifically, they want to know just how badly people’s momentary yearnings skew their memories, and how these distortions color self-esteem.

To test this idea, the scientists had to play around a bit with research subjects’ visceral states. For example, in one experiment they deliberately initiated fatigue in some of the subjects by having them take part in a demanding memory exercise. Once they had exhausted some of them mentally, they told all the subjects a brief story about a student who had failed to prepare adequately for an important exam. In the vignette, the student claims that he was too tired to study any more. His parents, unconvinced by this excuse, accuse him of lack of discipline and weak willpower and similar defects of character. The research subjects were told to decide for themselves.

The researchers found that the participants who were tired took the student’s part, while those who were not tended to side with the parents. In other words, as they report in the new issue of Psychological Science (full disclosure: I am the director of public affairs for the Association for Psychological Science, the nonprofit organization that publishes the research journal),  the participants’ own current physical condition determined whether or not they empathized with the student. What’s more, the more exhausted they were, the more likely they were to agree that fatigue was the cause of the fictional student’s failure.

The researchers wanted to double-check this, so they ran another experiment that was similar but with an important change. This time they explicitly told the subjects to disregard their own physical sensations and focus on the student. Even with this unambiguous instruction to empathize, the subjects still could not put their own feelings aside. The weary ones again sided with the unfortunate student, while those who were well-rested believed, like the parents, that failure was linked to lack of character.

These findings have huge implications. That’s why the psychologists ran one more experiment just to make sure of what they were seeing. In this test, some participants did the memory exercise in mild pain; they were required to submerge one arm in ice water. Afterward, they were all told (falsely) that they had blown the test. All were then asked to assess their performance, but only some had to again stick their arm in the frigid water while doing so. Those in pain consistently attributed their failure to the pain they had endured earlier, while those who were feeling okay said they must have failed for other reasons.

Here’s where it gets really interesting. Those who blamed their distress for their failure were actually more satisfied with their performance than those who had no such excuse. In other words, those currently in pain assumed that similar pain accounted for their failure in the past, and this distorted perspective made them feel better about themselves. Those not in pain—like most of us most of the time—had nothing to blame other than themselves. They in effect accused themselves of  a character defect.

So back to hunger and food. Imagine a dieter who, after months of discipline, loses control of his cravings and goes on a chocolate binge. Once he is satiated, he tries to make sense of this lapse. Since he is incapable of “reliving” his cravings—true empathy—the best explanation for his behavior is unavailable to him. So he manufactures some other explanations: He’s under stress, he has no support, he’s weak, he’s worthless. If he's not careful, he can talk himself into believing he's incapable of sticking with a diet—though he'd slipped just once. It’s no wonder that so many people have trouble losing weight.

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