WASHINGTON --

Call it the alter-ego of supersizing.

Researchers infiltrated a fast-food Chinese restaurant and found up to one-third of diners jumped at the offer of a half-size of the usual heaping pile of rice or noodles, even when the smaller amount cost the same.

Giant portions are one of the culprits behind the epidemic of bulging waistlines, and nowhere is the portion-creep more evident than in restaurants with french fry-heavy meal deals or plates overflowing with pasta. Now scientists are tapping into the psychology of eating to find ways to trim portions without people feeling cheated, focusing on everything from the starchy sides to the color of the plates.

"The small Coke now is what used to be a large 15 years ago," said psychologist Janet Schwartz, a marketing professor at Tulane University who led the Chinese food study. "We should ask people what portion size they want" instead of large being the default.

Restaurants are paying close attention, says prominent food-science researcher Brian Wansink of Cornell University. His tests found children were satisfied with about half the fries in their Happy Meal long before McDonald's cut back the size, and the calories, last year.

"We'll be seeing some very creative ways of downsizing in the next couple of years," Wansink said.

Let's call it "right-sizing," says Duke University behavioral economist Dan Ariely. Right-size suggests it's a good portion, not a cut, he says.

Couldn't you just get a doggie bag? Sure, if you've got the willpower to stop before your plate is mostly clean. Lots of research shows Americans don't. We tend to rely on visual cues about how much food is left, shoveling it in before the stomach-to-brain signal of "hey, wait, I'm getting full" can arrive.

So Schwartz and Ariely tested a different approach: Could we limit our temptation by focusing not on the tastiest reason we visited a restaurant, the entree, but on the side dishes?

A Chinese franchise at Duke University allowed the researchers in at lunchtime.

In a series of experiments, servers asked 970 customers after their initial rice or noodle order: "Would you like a half-order to save 200 calories?" Those who said yes didn't order a higher-calorie entree to compensate. Weighing leftovers showed they threw away the same amount of food as customers who refused or weren't offered the option.