Neanderthink: An Outsize Appetite, Courtesy of Evolution

Maybe your mother didn't cry, "Mangia!" when you ate dinner, like mine did. Still, you're likely to whisper it to yourself. That's because you possess a simple survival impulse: Eat until sated. Our neanderthink legacy is to store as much energy as possible, since calories were scarce and uncertain for most of human evolutionary history and our metabolism was set to guard against the possibility of starvation tomorrow. The problem is that eating more doesn't sate us; we merely recalibrate how much we think we need.

Our evolved mind-set on food hinders us in several ways. Our instincts tell us to keep eating well beyond when we are sated. Worse, the foods we crave—calorie-dense fats and sugars—were once rare and valued as a bulwark against starvation; now they're plentiful and harmful in excess. We don't crave plants, precisely because they were more abundant in our past. And if we do manage to temporarily gain a handle on the gustatory Disneyland in which we live, our dietary rigor plummets once we've lost weight.

Our "gut" instincts can swiftly divine whether someone is an ally or a cheater and whether something is distasteful before we even taste it. But listening to our literal gut in the contemporary world has led only to an obesity epidemic.

Eighty thousand years ago—yesterday in evolutionary terms—we ate at a very different restaurant, the savannah. Food was scarce and uncertain, and great physical effort was required just to acquire enough for survival. Our ancestors were lean and muscular, their bodies sculpted by scarcity. The mismatch between savannah dining and today's smorgasbords means our bodies are best adapted to a life at boot camp, not a 24-hour minimart.

More, our eating decisions evolved to function unconsciously; it was routine for our forebears to pursue and eat food when it was available. So we can consume 710 calories worth of chips and guacamole—as an appetizer. To combat a world of supersized stimuli, we have to overcome the natural need to eat until we're full.

We're good at rationalizations to avoid governing our food intake. We tell ourselves, "I can get away with eating this delicious morsel," or "It's too hard to deny myself this scrumptious ice cream." By yielding to such urges, we ratchet upward the amount of sugar and fat we crave, because we are tampering with a hormonal system finely attuned to the lack of such concentrated energy. On the savannah, the sweetest confection was wild fruit.

Michael Pollan, author of The Omnivore's Dilemma, famously summed up what you need to know to consume healthfully: "Eat food. Not too much. Mostly plants." The method by which we might hew to this Paleolithic regimen can also be summed up in seven words: "Dieting gets easier if you don't cheat."

Cheating awakens a voracious hormonal tiger; we begin to crave the available calories. And thanks to modern food processing, available they are!

But wait—there's another danger to cheating. It can cause us to lose faith in the diet altogether and lead us into the fatalism of a dieting myth: the idea that on-again, off-again dieting is worse than not dieting at all. "Yo-yo dieting gets a bad rap," says Deirdre Barrett, a professor of psychology at Harvard and author of Waistland.

She contends that "it might be better to spend parts of your life having good blood pressure and good cholesterol, albeit temporarily." Yes, she says, it's much better to keep those measures down—but periods of being at your
ideal weight interspersed with those at a higher weight "are not worse, and are perhaps better, than not dieting at all."

Barrett recommends willpower to overcome an evolutionarily stacked game. By dieting, we're going against our deep impulse, one that helped most of our ancestors endure: eating for survival. Alarms go off when the body is deprived of beloved treats, but on a diet you make conscious decisions to reframe that alarm system. Says Barrett, "Willpower is required during that first biochemical storm; most people fail in the first three days on a diet. We forget that when we're dieting."

Willpower is also bolstered if you know what to expect. Research shows that it takes 72 hours of cravings to tame the tiger and reset hormonal levels. It then takes another couple of weeks before dieting becomes easier, maybe even enjoyable (especially if you start feeling better and liking your new size).

So have some confidence in your long-term goal; commandeer your prefrontal cortex and conscious decision-making faculties until your body gets the message. But no cheating allowed. Taking an absolute approach is ultimately easier than second-by-second decision-making. Remember, instinct will supply you with every possible rationalization—"I'm starving to death," "I can't take this torture"—until you wrestle it down.

And with success comes the need for further vigilance. As Barrett points out, people who succeed at losing weight might lose the pressure to keep at it because they look and feel OK. You may need to stay more conscious and more focused and exert more willpower once you've lost weight—until healthy food choices become automatic.

Evolution has given us a mixed emotional bag well adapted to a natural environment with lots of pitfalls. Our pitfalls today are man-made, such as artificial confections that play on our desires. Fortunately, we've also evolved brains that can get us to push away from the table, despite the seductive echo of "Mangia!" —Nando Pelusi

Debate with a Dieter...

Let your cortex be your ally; try self-talk for long-term healthy eating.

• I enjoy life more when I stay away from empty calories.
• Diets work when I make them work.
• Food is a drug.
• Feeling fit feels better than a lapse of will.
• Dieting gets easier if I don't cheat.
• I can enjoy mastery over my irrational impulse to overeat.

...But Don't Kid Yourself

Dieters consume a lot of mythology about dieting, argues Deirdre Barrett. Here are some reality bites:

• It's OK to cheat. No. Usually, it's much harder on your body when you cheat.
• Treats are rewards. In fact, treats prevent you from regulating glucose and insulin and make it much harder on you in the long run.
• It's too hard to drastically change eating habits. The truth is, it'll be easier overall to work on a drastic change for 72 hours, and it gets even easier once you've set a structure for healthy choices.
• I can eat until I feel full. False. In fact, you consciously register satiety long after your body is physically fortified—and full.