Shares in high-end grocery retailer Whole Foods (NASDAQ: WFMI) have slid around 20% since early November. The most obvious explanation for the pullback -- investors remain concerned that a weakening housing market and continued turmoil in the credit markets could result in a slowdown at Whole Foods.

However, the company is more resistant to these pressures than many investors realize. Americans have shown an increasing desire to eat healthier -- a trend that has allowed sales of organic foods to grow at three times the rate as those at conventional groceries. As the largest retailer of organic products, Whole Foods is well-positioned to benefit from this trend.

Moreover, while the company is the clear leader in the organic grocery niche, it's still a minnow compared to traditional grocery giants like Safeway and Kroger. With only around 200 stores spread across the U.S., the U.K. and Canada, Whole Foods still has plenty of untapped markets to expand into over the coming years.

Two additional factors are also weighing on the shares at the moment. The first is a general fear regarding the potential impact of increasing competition in the organic foods market. In recent years, traditional grocery chains have been adding to their selection of organic foods. At the same time, new entrants, such as Britain's Tesco, are also targeting the space more seriously. However, Whole Foods remains the undisputed leader in this market and offers the widest product selection. Furthermore, there's plenty of room for multiple competitors in this growing space.

Finally, the U.S. Federal Trade Commission (FTC) continues to pursue an antitrust case against Whole Foods' merger with rival Wild Oats Market. However, the FTC's case is weak and was strongly rejected by a judge earlier this year. The courts also rejected the government's attempts to block the merger pending an appeal -- Whole Foods has now completed the deal. It's highly unlikely that an appeals court will overturn the deal and break up the merger.

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