Life Time Fitness has a challenge for one brave Twin Cities elementary school: Overhaul your lunch menu -- replacing processed food with natural alternatives -- and do it without raising costs.

If the gamble does increase the school's food budget, Life Time will pay the balance.

Either way, the project could improve students' health and reduce their exposure to high-fructose corn syrup, trans fat and food additives linked to health problems, said Bahram Akradi, founder of the Chanhassen-based chain.

"It's not rocket science," Akradi said on Thursday, standing behind dozens of one-liter bottles representing the average American's yearly soda consumption. "There are a number of ingredients you just do not want."

Life Time is inviting metro-area schools to apply. The selection will be based on the school's readiness, but also the willingness of students and their parents to improve their eating habits at home. Akradi acknowledged that the test will have better odds in an affluent suburb, where parents have easier access to organic produce and can afford it.

The proposal is but the latest effort to reduce childhood obesity and change school food. The St. Paul public schools work directly with growers in Anoka, Foley and Lake City to buy produce. Farmington elementary schools have created healthy snack carts to replace the unhealthy items that parents often send.

If Life Time's idea works, Akradi said, it would be expanded to other schools within the company's service area. Ultimately, he hopes to prove to federal and state policymakers that they can improve the health of lunches without raising costs. Motivating families to switch to healthier foods will also motivate grocers to offer more of them, he said.

Akradi's challenge came just days after the state released a survey showing that 25 percent of high school senior boys are overweight or obese. The rate for senior girls is 17 percent.

The 2010 Minnesota Student Survey did show signs of healthier eating: 41 percent of senior boys drank no soda in the average week, down from 23 percent when the same survey was conducted in 2001.

Life Time plans to select a school early next year.

Jeremy Olson • 612-673-7744