A McDonald's "brand ambassador" speaking to schools across the country about how he lost 37 pounds by eating every meal at McDonald's for 90 days has drawn the ire of parents who believe it's just blatant advertising to students about fast food.

John Cisna, a former biology teacher from Iowa, has been speaking about his weight-loss diet of keeping total daily calories to 2,000 or less while eating three meals a day at McDonald's and going on daily walks. He dropped four waist sizes and lowered his cholesterol by a third.

Spreading his message via a book and a video, he has already spoken to more than 90 colleges and high schools across the country in the past year, with McDonald's paying for his time and travel expenses. His message is seen as a counter to filmmaker Morgan Spurlock's "Super Size Me," a 2004 documentary where Spurlock ate every meal at McDonald's for 30 days, gaining 24 pounds and seeing his cholesterol skyrocket.

"I'm not endorsing fast foods,'' Cisna said on TODAY Tuesday. "I'm endorsing that kids need to start using critical thinking skills when it comes to making the right choices of what they eat."

One Texas mom, Bettina Siegel, finds it hard to believe Cisna is not pushing McDonald's on students. Siegel, who is a member of a committee that makes nutritional choices for students at more than 300 public schools in Houston, thinks Cisna's message should not be in schools.

"I was really taken aback by what I saw,'' Siegel told TODAY. "Schools really ought to be a sanctuary where kids can just come and learn and not be bombarded by corporate messages, whether they are from McDonald's or an organic foods company."

A change.org petition started by Siegel, which asks to keep McDonalds' "infomercial" out of schools, has received nearly 60,000 signatures.

"This isn't strictly nutrition education by any means,'' Siegel said. "This is very much an advertising vehicle by McDonald's."

However, others believe the overall message trumps concerns about marketing to students like Brock Dudley, who listened to Cisna's presentation at a school in Rochester, Minnesota.

"It's a healthy message,'' Dudley told TODAY. "I don't see why he shouldn't be able to deliver it, even if it's free advertising for McDonald's."

"We have to work with the reality that teenagers are already eating fast food, so we can't put blinders on as adults,'' McDonald's nutritional consultant Shaye Arluk told TODAY. "We need to educate the teenagers on how they can make choices that are informed choices and balanced choices."

A McDonald's spokesperson told TODAY it does not provide any financial support to the schools where Cisna makes appearances and has no plans to stop his speaking engagements.

Follow TODAY.com writer Scott Stump on Twitter.