Why Do We Eat So Much When It's So Easy Not To?

Eat fewer calories than you burn.

Exercise more, eat less.

It sounds so easy. Both of those formulas are foolproof. Anyone who follows them will lose weight, baring some kind of medical problem. Then why is it so hard to keep that old waistline where it's supposed to be?

Because eating, many scientists contend, isn't just about eating.

Other animals, much lower on the evolutionary scale, have figured it out. Take the African cattle tick, for example. Female ticks don't have to worry about gaining too much weight, as long as the female remains a virgin. But once she crosses that point of no return, she gorges like mad, increasing her weight by ten-fold within 24 hours, according to researchers at the University of Alberta.

So, if she wants to remain slim, all the female tick has to do is remain chaste. Probably wouldn't work for humans, though. We're too caught up in the sociological aspects of eating, say scientists at a number of universities. Who we are eating with, and what kind of food seems to be socially acceptable, has more of an impact on how much we eat than feelings of hunger or fullness.

In fact, according to researchers at the University of Toronto, our biological needs have little to do with how much we eat. They've even come up with a name for it.

"Eating occurs within what we have termed a zone of biological indifference, in which the individual is neither genuinely hungry nor genuinely sated," says psychology professor Peter Herman.

A "zone of biological indifference"? Need to chew on that tidbit for awhile. Herman says we are rudderless when we are eating, paying more attention to our companions than we are to what we are eating, and thus we eat more than we really need.

Scientists at Cornell University have reached a similar conclusion. David Levitsky, professor of nutritional sciences at Cornell, says environmental cues, not biological mechanisms, are a big part of how much and what we eat. Even "feeling stuffed" doesn't shut off the appetite, he says.

Levitsky and his fellow researchers reached that conclusion after talking 12 people, average age of 31, into going on a two-week eating binge. The researchers wanted to know if after eating all that stuff, and gaining an average of five pounds, the participants in the study would cut back in the following weeks, shedding those extra pounds.

They didn't, Levitsky reported in a peer-reviewed journal, Psychology and Behavior. The participants ate just about the same as they had before stuffing themselves for two weeks.

"The study suggests that eating behavior does not normally respond to internal cues, such as physiological mechanisms involved in the regulation of body weight, but to external cues," the scientists concluded. In other words, Levitsky says, the participants ate more than they needed after the experiment, "regardless of any biological signals."

He's not suggesting that the matter is beyond our control, of course. He's saying, instead, that "environmental cues" are prime movers.

"Consistently, we find that how much people eat is in direct relation to how much they are served, the variety of foods offered and the number of people with whom they eat," says Levitsky.

For some time now we've heard, over and over again, that it's not just how much we eat, but what we eat, that leads to a healthy diet. But now, a growing number of scientists are adding another factor. Who we eat with, and the circumstances of our setting, can also be a big player.

Which brings us to the current holiday season. Thanksgiving isn't just about giving thanks. It's about getting stuffed.

It's the one day of the year when it's socially acceptable to pig out. In fact, Mom is likely to be insulted if there's a speck left on your plate, regardless of how many times you went back to the trough.

Once a year isn't likely to make much difference. But eating with friends and family who want to see a healthy appetite can be deadly.

So, at the end of the day, tell Mom to buzz off. And exercise more, eat less.

Or join the cause of the African cattle tick.