Weight can be a very personal issue. Not just because many people are sensitive about how much they might weigh, but because there are so many factors that go into someones body size. Some of these issues are beyond a persons control such as genetics and the enviornment you were raised in. Of coarse, many factors are controlable and an overweight person needs to take personal responsability.
I'm 6'0 and around 370 lbs. Both of my parents were obese. 3 of my 4 siblings have struggled alot with weight issues. As a kid I was always rewarded with food. All of this is beyond my control. That said, when a little kid asks me why I'm fat I tell him or her that I'm fat because I eat too much of the wrong foods and I don't excercise enough. Most problems are caused by personal choices. Your friend is the only person who is going to be able to help himself with this problem. You can encourage, you may be able to give him some helpful tools like walking with him or giving him Dr. Phils book (I would suggest staying away from severly restrictive diets like the high protein or vegetarian diets promoted by so many).
Another thing to remember; dealing with obesity is a tough problem. I've met a lot of fattys in my 46 years. I've yet to meet one who wouldn't prefer to be skinny. Unlike cigarettes, alcohol or drugs, you can't just tell someone to stop eating. Alot of us fatties are waiting for some wonderful drug(s) that can give us a more permanent solution. Whoever finally markets that drug is going to be richer then Bill Gates. Millions of people would pay anything for such a solution.
My short term answer for being with your friend at WDW, and I cannot stress this enough; RENT AN ELECTRIC WHEELCHAIR!!! I don't know why I was so resistant to this. For years when I went to WDW I dealt with an aching back, hurting, aching feet, resting every 15 to 30 minutes and an impatiant wife and now an impatiant daughter. Maybe it was the money. Maybe it was the fact that people may stare at me. Maybe it was that I felt that I shouldn't be in a wheelchair because I didn't have a broken leg or a dehabilitating disease, I was just fat. Finally, I just told myself that all of these concerns were stupid. Here I was at my favorite place on earth having a miserable time. I rented the wheelchair. I was happier. My wife, and my daughter were happier. No more aches and pains. No more frequent rest stops. The WDW staff couldn't be more helpful and kind. You'll be so much happier not hearing any complaining from your friend. You even get an added perk of being able to bypass most of the lines. I'm now trying very hard to lose weight. There's too much out there that I still want to do and being morbidly obese is really taking a gamble with my life expectancy. I don't want to leave my wife a young widow or my daughter fatherless. One day I hope to be able to spend a day at WDW without becoming tired and sore but until that day I'll spend the extra $35.00 a day for happiness versus misery.