[quote]"He also started walking 45 minutes a day"[/quote]That right there pretty much undermines this entire experiment. If he was serious about how scientific the experiment should be, he would have done it properly and control for independent variables. Essentially, he should have been exercising [i]before[/i] changing his diet and obtain a healthy weight, cholesterol level, etc... At this point his bodily state (measurements) would have been taken. He would have then changed his diet to McDonald's only, as this is the dependent variable he should be interested in, and then when the experiment was complete, his state taken again, then compared with earlier. tl;dr This "science" teacher's results are fundamentally flawed. By not providing an appropriate control beforehand (especially in relation to his exercise regime), it is possible (and likely) his exercise contributed to whatever extent to his weight loss, cholesterol drop, etc...; not simply because he followed the McDonald's "healthy" diet.