Somewhere between the invention of Photoshop and Kate Moss's "nothing tastes as good as skinny feels" life motto, six became the new four, and two became the new zero. Along with garment sizes, the female clothing industry's client base shrunk to fit only a specific body shape -- the "tubular" one. News flash: the only skinny thing about most women is their stilettos. Fashion designers and apparel retailers of this world,  the "curvy" revolution is already happening.

The unfolding 'curvy' revolution

When Eden Miller made history last September by being the first ever plus-size clothing designer with a show in New York Fashion Week, I couldn't help but wonder, is it the beginning of a new era? When lingerie brand Aerie decided not to retouch its models with Photoshop for its new advertising campaign, I knew it was.

In a fashion industry that worships all things skinny, there have always been excuses to maintain a "narrow" focus -- there isn't enough design expertise in the plus-size space, larger bodies are not uniform in shape and thus present a "design challenge," or larger mannequins are costly to produce. For so long, key industry players from high-end designers to mainstream retailers dragged their feet on embracing the "average" woman. In turn, curvy women were left to believe that wearing black and avoiding stripes was as good a fashion tip as it gets. But, that's all in the past.

More and more designers and retailers with name power are eyeing the plus-size market, looking for opportunities in all new places. After nearly two decades of cutting back on mannequins to save money, stores are finally investing in making them look more like the women who wear their clothes. David's Bridal, for instance, is adding saggier breasts, thicker waists, and back fat to its mannequins. Ralph Pucci International, which creates figures for Macy's (NYSE:M) and Nordstrom (NYSE:JWN), plans to offer versions with fuller hips and wider waists to mimic a more realistic shape.

Most importantly, normal-sized women are finally done apologizing for their bodies, standing up to rude salespeople and their judgmental looks, demanding that retailers cater to their curves. As plus-size fashion expert and owner of The Curvy Fashionista blog Marie Denee told me, industry players need to pay attention to the new plus-size woman, not the one they thought she was years ago, but who she is now; she is layered, multifaceted, and full of life.

An underserved market

The gist is that the plus-size market is overlooked. More than one third of Americans qualify as obese, according to the Centers for Disease Control and Prevention. The average American woman weighs around 25 pounds more than she did in the early 1960s and has a 37-inch waist. That's roughly a size 14. Yet, most designer styles top out at size 10 or 12.

Fashion industry analyst at NPD Group Marshal Cohen has pointed out that the plus-size market represents only 14% of the total women's apparel, even though around 65% of U.S. women wear sizes bigger than 16. Not to mention, two apparel-design students at Cornell University found in their research that plus-size women hold nearly 30% of purchasing power for apparel and accessories in the U.S. while their spending accounts for only 17% of purchases.

Clearly, there's an immense business opportunity in the "size-zero war." But who's going to get the most out of it?

Who are going to be the big winners?

Women's apparel maker Ascena Retail Group (OTC:ASNA) is well positioned to cash in on the "curvy" revolution. It tapped into this promising market in 2012, when it bought two of the nation's most recognizable plus-size brands, Lane Bryant and Catherines. For the first quarter of fiscal 2014 alone, total comparable sales at Lane Bryant and Catherines stores edged up 7% and 11%, respectively.

Stores like Macy's and Nordstrom have already established a strong foothold in the plus-size space. And if they take the whole "mannequin makeover" movement seriously, they could give brands like Old Navy, which sells plus-size clothing exclusively through its website, a run for its money.

Struggling retailer Abercrombie & Fitch (NYSE:ANF) learned its lesson and decided to look beyond only "cool, good-looking" shoppers. It plans to offer larger sizes for some of its women's clothes online. This change of heart could prove to be life-saving, provided that it's sincere and marketed effectively.

Nevertheless, those who are taking this market by storm are non-traditional apparel retailers and even newcomers. Recently, Glee star Amber Riley and her sister launched RileyLand Fashions, an online plus-size boutique. Minutes after the launch, all stock was sold out. San Francisco-based brand IGIGI strives to provide full-figured women with flattering and sophisticated collections. It has earned multiple awards and wholesales to 43 boutiques around the country.

These non-traditional players take the time to research what women really want. They show diligence in creating and profitably marketing versatile and stylish designs. Offering a generic plus-size selection or expanding regular-sized designer pieces isn't good enough for them. Brands like these are going to make waves in the retail business not only because they relate to the average woman, but also because they test the waters in an amazingly thorough and daring way.

Final thought

Apparel retailers need to keep in mind that singling out the full-figured woman and treating her as "the other" or offering a plus-size line while still employing waif-like models is wrong. With the right resources and enough marketing dollars, retailers could slay this arena. Otherwise, newcomers or underdogs could sneak up to them and steal their thunder. 

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.