(FORTUNE Magazine) – The bankruptcy filing of Atkins Nutritionals in late July signaled the twilight of America's latest diet obsession, as carb counters realized, to their amazement, that man cannot live on pork rinds alone. The filing also presents investors with a veritable buffet of small- and mid-cap stocks that suffered during the low-carb era and now stand to benefit. But not all of them are good for your portfolio, so put down that bagel and let's see how the post-Atkins era shakes out.

First up are two venerable diet plans, Weight Watchers International and NutriSystem. Weight Watchers (WTW, $51) has seen an uptick in attendance of late, but we'd prefer a slimmer forward P/E ratio than the 26 it currently sports. And rival NutriSystem (NTRI, $31), the best-performing stock on Nasdaq this year (as of Oct. 7), may not have much lift left in it. So try the diets--but pass on the stocks.

During the Atkins craze, you had to feel sorry for any company with the ticker symbol PSTA. Such was the burden of Monterey Gourmet Foods ($4), which changed its name from Monterey Pasta last year to reflect its wise decision to expand, mainly via acquisitions, beyond pasta and sauces into gourmet sausages, organic dips, and specialty cheeses. Monterey broke even in its most recent quarter on sales of $21.2 million, reversing a year-ago loss, and analysts see plump profits ahead. "As they integrate these acquisitions and get margins back to historical norms, there is tremendous upside in earnings potential," says Rodney Hathaway, an analyst at Heartland Advisors, whose Heartland Value fund owns 547,000 shares.

Such growth is probably not in store for American Italian Pasta (PLB, $8), whose shares fell 37% in one day in August when the company announced an internal investigation into dodgy accounting. This outfit, which has annual sales of $400 million and makes store-brand pasta for retailers such as Wal-Mart, can't blame Dr. Atkins entirely for its current woes. Still, for investors with patience and a strong stomach, a few analysts think the company--which just hired turnaround specialists Alvarez & Marsal--might be worth betting on.

Finally, in a world of fad diets and magic weight-loss pills, let's not forget those companies with a quainter approach to losing weight--sweating the pounds off. For many years Nautilus (NLS, $21) was a one-trick pony, selling its Bowflex systems via ubiquitous infomercials. But vicious competition from NordicTrack has prompted Nautilus to expand its distribution channels and its product line.

The company's gear debuts on Sears' shelves this fall, and nearly 30% of its projected $700 million in sales this year will come from products introduced over the past 12 months, like the Bowflex Revolution. Nautilus has had three consecutive quarters of 40% gains in earnings, and analysts see an attractive entry point now that its shares have suffered (down 26% since late July) along with other consumer product stocks in the face of rising interest rates and gas prices. Which, come to think of it, might prompt some people to get out of their SUVs and walk a few blocks. Now there's a diet plan with legs.