LOS ANGELES (Reuters) - Former Iowa science teacher John Cisna, who says he lost 60 pounds on a six-month regimen of McDonald's food and daily walks, has sparked outrage among public health advocates for taking his story to U.S. schools on the fast-food chain's dime.

The criticism comes as Steve Easterbrook, McDonald's Corp's chief executive, fights to remake the 60-year-old chain into what he calls a "modern, progressive burger company."

Part of that challenge is winning over youngsters who have seen documentaries such as "Super Size Me" and "Fast Food Nation," and as a result view McDonald's food as a contributor to obesity, diabetes and other serious diseases.

Cisna has tried to counter that impression, first with a book last year called "My McDonald's Diet: How I lost 37 pounds in 90 days and became a viral media sensation," detailing an experiment he said was created with his students. The goal was to stay within strict calorie limits while eating items from the hamburger chain's menu.

McDonald's hired Cisna as a "brand ambassador" earlier this year and provides him a stipend for time and travel related to his speaking engagements, spokeswoman Lisa McComb said. She would not disclose the size of the payments, but said Cisna came up with his experiment without help from McDonald's.

Thus far, Cisna has spoken mostly at the invitation of about 90 schools, predominantly colleges and high schools, said McComb.

Among other things, his program includes a 20-minute documentary "540 Meals: Choices Make the Difference" and a teachers discussion guide, both of which were edited by McDonald's, McComb said.

"John's story is not a weight loss plan, and we do not recommend that anyone eat every meal at one restaurant every day for an extended period," said McComb. "While the decision on how schools choose to educate and inform their students is up to them, we support John's desire as a teacher to provide students with facts to make informed choices."

Cisna was not available for comment.

Critics say the program is a new attempt by McDonald's to hook youngsters on unhealthy food. For example, Cisna says in the video that careful planning allowed him to eat french fries nearly every day.

"This is really beyond the pale in terms of its aggressive marketing to kids," said Bettina Elias Siegel, a former lawyer, who was first to write about Cisna's school program on her blog, TheLunchTray.com.

Mark Noltner, an Illinois elementary school teacher, called the program "a blatant decision by McDonald's to get their name into schools with what is basically an infomercial for the company."

McDonald's and its franchisees separately have come under fire for sponsoring "McTeacher nights," in which teachers work at a McDonald's serving food to students and their families, with a portion of the evening's proceeds going back to their schools.

On Wednesday, advocacy group Corporate Accountability International, the National Education Association and more than 50 teachers unions held protests in Chicago and Los Angeles, and called on Easterbrook to put a stop to brand-building school fundraisers.

(Reporting by Lisa Baertlein in Los Angeles; Editing by Steve Orlofsky)