What was the purpose of morgan spurlock's in doing this experiment, super size me?

I believe it was to prove that eating Mc Donalds and junk food every day can be very bad for your body. Eating the junk that he ate gave him major heath issues. High blood pressure, he gained a lot of weight, and he was feeling sick all the time. Those were just a few of the horrible things that he experienced. In the beginning of the movie Mr. spurlock  expressed specifically why he did the experiment. Later on in the film Spurlock was asked on several occasions why he was putting himself at risk and he answered them by stating that he wanted to prove that fried fatty foods from mcDonalds was bad and can harm you when you eat too it too much.

It settles nerves, reduces the tension.