As Americans' waistlines contract and expand, their closets are filling with a wide variety of sizes.

Depending on her diet and exercise regimen, Wilbert's weight bounced around so predictably that she knew to keep a range of sizes in her wardrobe.

So does much of America. As the number of weight-loss programs continues to grow, so, too, do America's closets.

"Losing weight has become a hobby and a sport for a lot of people," says Marshal Cohen of The NPD Group, a market research firm. "More than half the people who diet expect the weight to go back up. For them, they have a couple of wardrobes."

Or more. Increasingly, those wardrobes are split not only into "skinny clothes" and "fat clothes," but sections gamely dubbed "skinnier" and "fatter." It's an expensive byproduct, say dieters, of trying low-carb/high-protein programs that are notoriously hard to maintain, such as Atkins. Opinion Dynamics, a market research company, reports 12 percent of American adults are following such diets.

Flexible, if not multiple, wardrobes also are becoming a necessity

considering that many trendy diets shed weight far more quickly than the diets of old. Whereas tightening your belt an extra notch or two used to suffice until seasons changed and new clothes could be bought, today's diets are designed to drop weight so rapidly that new shorts are needed to get through summer.

The problem seems to be particularly prevalent among women, whose weight tends to fluctuate more dramatically than men's. An unscientific survey of USA Today readers found that nearly 40 percent keep three sizes in their closets; 17 percent stow four or more. Closet racks are starting to resemble department store racks — something The Container Store has acknowledged. They sell the small plastic discs used to separate sizes on a department store rack.

"There's that two-year rule: If you haven't worn it in two years, get rid of it," says The Container Store's Melissa Reiff. "But when you go on those diets and your weight fluctuates, it's really hard to adhere to that two-year rule, particularly if it's quality clothing."

One common solution: double hanging, with the top row dedicated to "stuff I can wear now," says Reiff, and the bottom bar to "stuff I can hopefully wear in six months."

Tom Blessing divides his closet down the middle: His Atkins-reward size 38 pants are to the right, while the carb-friendly 40s are to the left — the direction he's gravitating toward these days. With a weight that can shift five to eight pounds in one week "easily," depending on, say, how much pasta he's eaten, Blessing, an athletic 6-foot-4, says he has had to accept that he's a two-wardrobe kind of guy. The added expense "bothers me a little bit, absolutely," says Blessing, 33, who works in finance and lives in Hoboken, N.J.

But Shellie Topper often hears of more extreme situations: "I've got three sizes, and I want to keep them all, just in case."

It's OK to keep the clothes around as a crutch, says Topper, whose family owns a California Closets franchise in Fairfield, N.J. — as long as they're stashed way out of sight, not just in a few extra drawers. "If you have done really well on a diet but still have that attachment and that fear (of gaining back the weight), it's helpful" to get the larger clothes out of the closet. The thinking is: "Look how far you've come. You're now two sizes smaller. Have a little confidence in yourself and get that stuff out of there."

But not necessarily over to Goodwill. In 1997, after Manhattan retail manager Kalyn Smith lost 40 pounds thanks to Jenny Craig, she promptly donated her old, larger clothes. "I thought, 'Oh, I'll never gain this weight back,' " says Smith, 33. She did. In one year. So she reinvested in a new wardrobe and vowed never to toss out clothes again. Good thing, because after she dropped the weight again in 1999 through Weight Watchers, she has since gained some of it back.

Now, the left side of her closet is devoted to her "fighting weight" clothing: black and khaki basics in a size 8 "that I know I will fit into again," while the right side is filled with her currently wearable clothes, more or less identical black and khaki pants and skirts mainly in size 12. Empty hangers mark the boundary. She knows not to venture left "until I go back to the gym and weigh in 20 pounds less. It's so sad but so true."

Hers is a tale of caution: "Get rid of the trendy stuff, but classic pieces, hold on to them."

Sage advice, because woe be to the successful dieter who celebrates her achievement by marching into the office wearing her old size 6 jacket, the one with the phone-book-thick shoulder pads. Sometimes, a dieter's gain-lose cycle is just not in sync with fashion's cycle.

To those with bodies in flux, secondhand and consignment stores are proving fruitful sources for inexpensive, barely used attire — and, in the latter case, a means of unloading expensive goods.

Dieters also are finding creative uses for those castoffs. After slimming down to a 22, Selina Killian cut up her 32s and 34s and stitched them into quilts for her family. "The weight lost and the shedding of the clothes made a difference not only to myself but to others," says Killian, 41, a Milwaukee airline worker.

But sometimes, when the weight loss feels particularly permanent, getting rid of old clothes in a more permanent way feels particularly satisfying. After undergoing bariatric surgery last November, Wilbert is now a size 12. Those 60 pairs of chinos and jeans in sizes 18 to 24? They're sitting in six garbage bags in her garage, destined for Goodwill.