Whole Foods Market (WFM) has lost a staggering 9 million to 14 million customers over the past six quarters. The company has been facing increased competition both online and in-store from other major grocers. Its biggest rivals include Kroger (KR - Get Report) , Trader Joes, Costco (COST) , Sprouts Farmers Market (SFM - Get Report) and Natural Grocers (NGVC - Get Report) . Shares of Whole Foods have fallen about 44% in the past two years. Whole Foods closed nine stores recently, calling into question the past five years of aggressive store openings.