Washington ? Call it the alter-ego of super-sizing.

Researchers infiltrated a fast-food Chinese restaurant and found up to a 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 portion sizes 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,” laments 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 own 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 down-sizing in the next couple of years,” predicts Wansink, author of Mindless Eating: Why We Eat More Than We Think.

But 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.

Other tricks can trim portions without people noticing, whether dining out or at home. Wansink found people served 18 percent more pasta with marinara sauce onto a red plate than a white one — and 18 percent more pasta alfredo onto a white plate.

A stark contrast “makes you think twice before you throw on another scoop,” explains Wansink. His own family bought some dark dinner plates to supplement their white ones, because people tend to overeat white starches more than veggies.