'McDonald’s diet' supersizes critics' outrage: Man who lost 27kg on six-month burger chain regimen takes his message to schools

A former science teacher who says he lost 27 kg on a six-month regimen of McDonald’s food and daily walks, has sparked outrage among public health advocates for taking his story to US 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.

The former teacher, John 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.

WATCH: How John Cisna lost weight eating McDonald's

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.