Diet and exercise=treatment and prevention in 90% of the cases. Throughout our lives we may have hormonal changes and instabilities that make it harder to accomplish that and there are obviously some very extreme thyroid or other glandular issues that can do it regardless, but this certainly is not the case for the MAJORITY of people overweight. The majority simply need to eat less/differently and move more...period. I get so tired of this bs. I remember people asking me how I did it and what I did and every one of them got disheartened at the answer. People watch the biggest loser and rah rah them on, but I don't think they really realize just how hard those folks are working. Some of those activities are grueling and depending on your endurance, strength, and ability by 2 minutes in you start crying mama for the average person. I really don't think a lot of people internalize what they are seeing--those people don't just become tone, thin, average,normal weight overnight---they sweat, push themselves, change their lifestyles, and still struggle with emotional triggers everyday to get and stay where they are.
The ONLY caveat I will give is emotional eaters. In many cases, those people probably require counseling as well to deal with the coping skills they are using for stressful situations in the same way a smoker might use smoking for the same purposes. Use eating as a coping mechanism and gain 100 lbs. And that is another 'branch' to the prescription above and the reason I think some people can go up 50, 60, 70 lbs and then lose it again because they never deal with that coping mechanism and when things get stressful they use eating to cope again and the pounds pile on.