The stock of organic and natural food distributor United Natural Foods (NASDAQ:UNFI) is digesting a more than 10% gain on news that the company has signed its largest customer, Whole Foods Market (NASDAQ:WFMI), to a new three-year deal.

With the five-year deal United Natural announced in June with Wild Oats Markets (NASDAQ:OATS), the company has now locked up the top two "supernaturals" (as the big box natural food stores are called).

Prior to the Wild Oats deal, Whole Foods accounted for 24% of United Natural's fiscal 2003 sales. That's a lot of vendor concentration. Now, United Natural can better focus on customizing its operations to serve these premier accounts and maintain its lock on this marketplace.

Feeding the top of the natural food chain retailers has not gone unnoticed by Wall Street. Besides blowing away the previous 52-week high by a wide margin this morning, the stock also set an all-time high. It's trading for what might be a rich 31 times analyst earnings estimates for this fiscal year, and next year's earnings are expected to ripen up by a decent-but-not-mind-blowing 17%, though it remains to be seen if this new deal will have an impact on analyst forecasts.

Look at a one-year chart of United Natural's stock and you can see that it has taken investors on a wild ride. While the company can grow through acquisitions and expand geographically by adding distribution centers, it is unclear where rapid growth (enough to justify the 37 P/E multiple) might be found.

With United Natural's slim 3.7% operating margins, investors might want to consider high-flying and cash-rich Whole Foods and its meatier 5.4% operating margins.

Fool contributor W.D. Crotty does not own stock in any of the companies mentioned. The Motley Fool is investors talking to investors. Join in the discussion of Organic Living and United Natural Foods on The Motley Fool discussion boards.