After a month of eating only McDonald's food, an Edmonton teacher lost weight, lowered his blood pressure and won a bet with his biology students – but nutritionists say he's risking his health.

Les Sayer set out to recreate the diet behind the hit film Super Size Me, in which Morgan Spurlock's 30-day McBinge ends in a weight gain of 25 pounds and a host of ailments.

Unlike the documentary maker, Sayer wanted to show he could lose weight and stay healthy on the fast food diet, which included the chain's salads.

In a written statement, McDonald's Canada said: "We are not affiliated in any way with this individual."

While Spurlock got as much exercise as an average American, Sayer pumped iron while on the diet and did one-hour cardio workouts six days a week.

He also varied his menu choices, choosing small and medium fries, coleslaw and diet Coke.

"My key message really is as long as you don't overeat and as long as you exercise regularly, you can lose weight and be healthy," said Sayer.

Sayer started the exercise regimen two years ago, lost weight and then plateaued on what he called a "lousy diet."

After 28 days of McDonald's, Sayer has lost 17 pounds and his blood pressure has improved.

Dieticians at the University of Alberta who analysed his diet concluded Sayer lost weight by eating less, but that he's getting too much fat and salt and not enough fibre, vitamins and minerals.

"Certainly the high fat is the number one risk factor for increasing your blood levels of cholesterol, which is the number one risk factor for heart disease," Kim Raine, director of U of A's Centre for Health Promotion Studies, said.

After 14 Big Macs, 38 diet Cokes, 16 Egg McMuffins and every other item on the menu, Sayer is about to quit the diet.

Next week he'll meet with his doctor to learn more about how the 30-day fast food diet affected his cholesterol and the rest of his body.