It's been a tough summer for United Natural Foods (NASDAQ:UNFI), complete with earnings warnings and declining investor sentiment. Like an organic loaf of multigrain bread, the company's fortunes rose yesterday in just a few hours. This proves, once again, that investors are about as fickle as New York sports fans (they booed Derek Jeter).

I tend to favor companies with a differentiated product line that gives it a huge competitive advantage. Can you name another natural and organic food supplier? Exactly, and that's why United Natural is such a key ingredient in the success of natural supermarkets Whole Foods (NASDAQ:WFMI) and Wild Oats (NASDAQ:OATS). Not only does the company distribute to these two markets but also it has about 18,000 other customers to distribute its 35,000 products to (now, that's what I call market coverage).

United Natural shares jumped more than 11% yesterday following its fourth-quarter earnings release. In early July, when the company lowered its annual earnings guidance for fiscal year 2005, Alyce Lomax was there to discuss how the shares got slammed by as much as 19%. This time around, United Natural reported earnings of $0.23 per share, which was a penny better than the analysts' expectations and $0.11 ahead of last year's $0.12 earnings.

The company's sales of $446.4 million also beat the consensus estimate and logged 22% growth over last year as management reported growth in all three of its distribution channels (conventional supermarket chains, natural product superstores, and independent retail operators). United Natural's results were also strengthened by a new primary distributorship agreement with Wild Oats.

Management reaffirmed its fiscal 2005 earnings guidance of $0.93 to $0.97 a share and revenues of $1.9 billion to $2.0 billion. The company also plans to continue its investment in "people, facilities, equipment, and new technologies," which should strengthen both its competitive advantage and barriers to entry in its market.

The shares of this attractive category killer are trading in a tight range relative to its 20%-plus growth rate. It is rare to find a company with this kind of deep market penetration in such a rapidly growing industry. As with most growth companies, however, the ride can be as stomach-churning as a roller coaster (just don't eat too much before buckling in).

Grab a spoon and a bowl of granola and check out these other natural wonders:

Fool contributor Phil Wohl has no stake in any firm mentioned above.