American Health Cos. Inc., parent of Diet Center Inc., a franchiser of diet centers in North America, has agreed to be acquired for $157 million by two investor groups. The company said Thursday the groups, CDI Holdings Inc. and DC Acquisition Corp., will pay $22.50 per share to acquire about 6.95 million shares of American Health stock. American Health's common stock rose 25 cents in over-the-counter trading Thursday, closing at $22 a share. The sale was announced Thursday after a meeting of American Health's board of directors in Salt Lake City. American Health spokesman Jim Liljenquist declined to discuss why the company agreed to the proposal. Diet Center is a leading franchiser of diet and nutrition centers, with about 2,300 outlets in the United States and Canada. Separately, American Health said Thursday it earned $3.5 million in the first quarter of its fiscal year. The profit in the three months ended June 30 was 16 percent higher than the $3 million earned in the opening quarter of last year.