That's size got to do with weight gain? A whole lot, figured Vyvyan Lynn, a mother of two from Kite, Georgia, who put on 70 pounds while pregnant.

"It's simple: If you don't have a health problem that keeps you from losing weight, then it's calories in versus calories out through activity," she says. "I just decided to keep up with what was going in my mouth. I didn't deny myself what I wanted; I just ate less of it."

Lynn reduced serving portions, taking in between 1,200 and 1,500 calories a day, and dropped from 225 pounds to 112 pounds within a year. Eight years later, the 48-year-old has kept her weight around 125 pounds, in part by monitoring portion sizes. If she eats fast food, for example, she orders a junior burger without fries. "I hate that too-full feeling," she says.

SUPERSIZED PORTIONS AND PEOPLE
If only we all heeded our hunger as well as Lynn. Instead, Americans are swelling right along with their meal size. The typical restaurant chocolate chip cookie is about seven times larger than the serving size defined by the United States Department of Agriculture, according to the American Journal of Public Health (February 2002). Today's "large" order of French fries at McDonald's was the "supersized" portion in 1998. A typical plate of pasta can yield six servings, a steak three servings, and a hamburger, two. You'll find three to four servings in the typical muffin, and today's bagel is about three times what it used to be.

Americans are expanding at the same disturbing pace. Some 60 million - one-third of all adults - are obese (defined as more than 20 percent above their desirable weight), according to the U.S. Centers for Disease Control and Prevention (CDC). The percentage of overweight young people also has more than tripled since 1980. Among children and teens ages 6–19 years, 16 percent are considered overweight.

Marion Nestle, professor of nutrition, food studies, and public health at New York University, blames supersized foods for supersized people. "Larger portions encourage people to eat more calories," she says. "It's easier to underestimate calories when you eat larger portions. Everyone underreports calories. Our kids, who've grown up on the new sizes, think huge is normal." Her suggestion? "If you can, listen to your body and stop eating when full. If you can't do that, then never eat anything in a portion bigger than your fist."

REALITY CHECK
The more food that's put in front of you, the more you eat. Moviegoers devour an average of 45 percent more popcorn from a large bag than from a medium one, says researcher Brian Wansink of Ithaca's Cornell University.

And those extra calories turn into pounds quickly. "Bigger portions may have hundreds of extra calories a day without you noticing it,'' says Nestle, author of What to Eat (North Point, 2006). "But at the end of the year, all those extra calories could add up to pounds of fat on you."

If you want to lose weight, you need to return to reality.

Step 1: Downsize. "Our plates and serving utensils are larger than they need to be. We have this distorted view of what normal is," says Lona Sandon, R.D., a spokesperson for the American Dietetic Association (ADA) and assistant clinical nutrition professor at University of Texas Southwestern in Dallas. She recommends using a smaller plate, such as an 8-inch salad plate, in place of a 12-inch dinner plate for evening meals. "It looks visually appealing, and you're satisfied with it," she says.

Step 2: Share. When you eat out, split the main course with a dining companion or have half of your dish bagged to take home. Or simply order from the appetizer side of the menu.

Step 3: Calculate. Check labels to see how many portions are in a package. A scale and measuring cup can also help you judge portion size. And record every bite you eat for three days. "A food diary is the best dieting tool there is," Sandon says. "By having to write it down, the calories become real. I've had clients drop a pound or two in those three days. Keeping a food record is highly correlated with significant weight loss."

As for Vyvyan Lynn, the small sacrifice involved in trimming portions was well worth it. Not only is she healthy and a good role model for her kids, she also has a lot more energy. "I love to move, and that weight was hard to carry around," she says. "Now I can dance again!"