WASHINGTON/SAN FRANCISCO, Aug 23 (Reuters) - Amazon.com Inc and Whole Foods Market Inc on Wednesday cleared two major hurdles needed to close Amazon's $13.7 billion acquisition of the natural grocery chain, with approvals from a U.S. competition regulator and Whole Foods shareholders. The U.S. Federal Trade Commission, in clearing the planned acquisition, said in a statement that it opted not to pursue its investigation further after reviewing whether the deal would substantially lessen competition or constituted an unfair method of competition. Also on Wednesday, Whole Foods shareholders approved the proposed sale to Amazon.