Science teacher John Cisna after, left, and before, right, his McDonald's diet. KCCI News A science teacher who lost 56 pounds in six months while eating nothing but McDonald's is the star of a new documentary, The Lunch Tray reports.

John Cisna weighed 280 pounds when he decided to go on the McDonald's-only diet.

After 90 days, he had lost 37 pounds, and at the end of the six months, he weighed 224 pounds.

Cisna limited his daily intake to 2,000 calories and exercised for 45 minutes five times a week.

The documentary follows his journey, while incorporating footage from an amateur video he filmed while conducting the experiment.

In the film, Cisna pushes the message that you can eat anything you want as long as you regulate calories and exercise.

"I can enjoy any food that I want," Cisna says. "If my wife and I go out and I want a piece of cheesecake, I'll have that piece of cheesecake, because I'll plan the rest of the day accordingly."

McDonald's is now peddling the documentary to schools as a tool for teaching kids about healthy eating, according to The Lunch Tray.

McDonald's even created a teachers' discussion guide for the film and prepared a form letter to be sent to parent teacher associations, The Lunch Tray reports.

We reached out to McDonald's for comment and will update when we hear back.

Cisna is now a paid brand ambassador for McDonald's and he insists that he still eats there every day.

"I eat McDonald's every day because I enjoy it," he says.

In the film he also addresses critics' claims that he probably ate salads every day during the experiment.

He says he ate almost everything on the menu, and ordered fries every single day.

"I ate 540 straight meals at McDonald's," Cisna says. "I spent a half a year of my life eating nothing but Mcdonald's and I know it works so when I hear the skeptics, it doesn't disgruntle me. It actually fires me up because those are the people that I have to educate."

Here's the film.