FWIW, the two nutritionists my wife has seen and other doctors I know say that while exercise can help, weight loss/gain is more related to genetics and diet. No matter how much exercise you do, you're not going to slim down if you're eating pizza, fried chicken and chinese food on a regular basis. Why do you think some football linemen are morbidly obese despite the amount of exercise they get. Their diet is specifically tailored to keep them as big as possible. People also tend to put on more weight as they age as metabolism slows. If I ate what I ate when I was a teenager, I would probably weigh 300 pounds (back then, I weighed 170).
Also, be very careful about claims that something "affects brain function". Most of the time, this claim is a truism in that everything you do and everything you eat affects brain function in some way. A few quacks who go in front of congress every so often to talk about the dangers of violent video games make that claim. The very act of playing any video game, whether it's Tetris, Super Mario Brothers or Grand Theft Auto affects brain function.
Some of my friends lost a lot of weight from changing their diet and running. So you're saying they probably could have gone without the running and would have lost almost the same amount of weight?