More grocers are now tapping into the growing market for the health conscious, organic-seeking consumer. Even big box retailers like Walmart (WMT), Costco (COST) and Target (TGT) are taking a bite out of the natural products business. But when it comes to fresh foods and produce, Whole Foods Market (WFM) has dominated and some analysts are questioning its ability to stay on top with the added competition. Brad Lamensdorf is co-manager of The Ranger Equity Bear Short Only ETF (HDGE). His fund is shorting United Natural foods (UNFL) on that account. He says that as a major distributor for Whole Foods, 'United Natural Foods is currently experiencing margins that are getting slimmer and slimmer.'