Eating a lot is like a hug to an obese person, who gets lots of negative messages elsewhere in the course of daily life

Before and after. It's a favorite image used by weight-loss products and exercise clubs to attract customers. If you are grossly overweight, you, too, can look fit and trim in a flash. If you don't do it, you should be ashamed of yourself.

In fact, according to Yale researchers Rebecca Puhl and Kelly Brownell, shame is society's cruelest tool in changing fat people's behavior. It's still largely acceptable to tell "fat jokes." Indeed, obese people sometimes tell them themselves.

Rather openly, we say that fat people are jolly, sloppy, self-indulgent, not to be taken seriously. Even when we try to be subtle, fat people know what we feel. They know that terms like "big-boned" and "chubby" and "pudgy" are code for "disgustingly unattractive." No obese person needs to be told what so-called "plus," "portly," and "full-figured" clothing sizes are all about. As the researchers point out, no one would dare direct such humor or special labeling at racial minorities or the disabled.

Overweight participants in the Yale researchers' study reported all sorts of indignities, such as the time when a mother laughed to her friends that she was off to the tentmaker to buy clothes for her child.

Temptations are everywhere for fat people, as those who make fun of them are quick to point out

So while shame is thought to be good for provoking fat people into making healthful lifestyle changes, quite the opposite is likely. Stigmatizing overweight people only deepens their self-loathing, driving them to their one reliable source of comfort and affection -- namely, food.

Ms. Puhl and Mr. Brownell have written that the "time and effort spent ridiculing overweight people would be better used in advocating for a society in which better eating and physical activity are encouraged."

In other words, being fat isn't fun, and it's not very funny, either.