COLO, Iowa – Iowa high school science teacher John Cisna conducted an unusual experiment with his students, and the results were not at all what they expected.

Cisna weighed 280 pounds and had been overweight most of his adult life when approached students with a seemingly implausible hypothesis: “What if I eat McDonald’s three times a day for 90 days and I am better off because of that diet?”

“There wasn’t a single kid, a single faculty member, a single person in the entire community that felt this had a snowball’s chance in hell of being proven positive,” Sisna told WTSP. “They basically thought I was one French fry short of a Happy Meal.”

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Three students took Cisna up on his challenge, set up some parameters – including a 45-minute daily walk – and the results were astounding. Over the course of three months, Cisna ate only McDonald’s foods for all three meals, dropped 37 pounds, and improved his cholesterol levels significantly.

“He weighed 280 pounds before, and after three months, he weighed 219 pounds. His cholesterol level dropped from 249 to 170. His triglycerides dropped from 156 to 80 and his LDL dropped from 170 to 113,” the news site reports.

The key to the successful diet, Cisna said, came down to portion control and food selection.

The students “had to keep me on 2,000 calories a day, but more importantly we tracked 15 different nutrients. Sometimes I had to sacrifice calories for nutrients, so on some days, I had less than 2,000 calories a day,” he said.

“I was not eating a 630-calorie Big Mac every meal every day. I would have oatmeal and an Egg White Delight McMuffin for breakfast, a chicken salad with two bags of apples for lunch, and then a value meal for dinner,” Cisna told WTSP. “I was not eating desserts all the time and sugary-blended drinks. I did follow what the kids told me though. They monitored the McDonald’s’ website’s menu builder and were able to create 56 meal combinations …”

The initial experiment was so successful, Cisna said he continued the diet for another three months and lost another 23 pounds, though he also worked with a trainer to incorporate more exercise during the last phase.

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In total, Cisna shed about 60 pounds in six months, and both the teacher and his students learned some valuable lessons.

“I’ve learned something now for the first time in my life: I can eat any food that I want — and guilt free. If I want a piece of cheesecake, I can have it because I’ll plan the rest of the day to make sure I can have that piece of cheesecake,” Cisna told WTSP.

“One student saw the project afterwards and said, ‘It’s not McDonald’s that makes us fat it’s our choices and what we eat that makes us fat,’” he said. “And that says it all and that came from the students!”

Unsurprisingly, McDonald’s executives, who were not involved in the experiment, have applauded Cisna’s accomplishments.

“We congratulate John Cisna on his weight loss and improved overall health, and we are pleased he was able to accomplish his goals by making balanced choices, which included many of his favorite McDonald’s menu items,” Cindy Goody, senior director of nutrition at McDonald’s USA, said in a statement cited by USA Today.