Health-food stores in expansion mode: independents say they're prospering, while the GNC chain looks to grow through local acquisitions. (General Nutrition Center)

The health-food-store business is ... well, quite healthy.

Take Rainbow Grocery on Seattle's Capitol Hill. Last March, Ross Kling, who owns the store with his wife Pat, moved it a few doors down the street into a new location with 50 percent more space. A few months later, in the old space, Kling opened Rainbow Natural Remedies, a store with two naturopathic physicians.

Kling's expansion isn't unusual. According to Kathy Koska, executive director of the Northwest region of the National Nutritional Foods Association, the number of stores in the Puget Sound region "is definitely growing. A lot of people who own stores are opening up second and third ones. Those not opening new stores are enlarging existing ones."

Health-food stores have long been a Puget Sound-area fixture. Rainbow Grocery is 15 years old. Mari-Don Healthway Natural Foods, named after the married couple who founded the store, has been in Seattle's Wallingford neighborhood for about 30 years. And the original Groff's Nutrition, one of the oldest health-food stores in the Puget Sound area, …