To treat obesity, you need to understand what causes it.
For muscles and organs to perform, they need energy. Like a car needs gas, every cell needs energy. Food that we take in (primarily carbohydrates and fat) is converted to energy. The amount of energy that one gets from food is defined as calories.
If, however, too many calories are taken in but not used by the body, those calories are stored as fat. Obesity occurs when "consistently" the amount of calories taken in is significantly higher than what is used by the body.
Therefore, to LOSE weight, one must expend (use) more calories than they take in. One way that people do this is, obviously, through diet:
Portion control (our society has an increasingly difficult time recognizing HOW MUCH of certain foods must be consumed at one time)
Wise food choices - complex carbohydrates (fruits, veggies, and whole grains) take longer to digest, leave you feeling fuller longer, and usually contain less calories than simple sugars (processed sugars, sodas, white bread/flour, etc) that will quickly convert to glucose
and also store as fat if not used quickly.
Using healthy oils such as olive oil, safflower oil, soybean or sunflower oil rather than saturated fats such as butter, lard, shortening.
Some research advocates eating small meals more frequently (like every 3 hours) rather than 3 large meals throughout the day to promote a healthy weight. The concept here is that blood sugar levels stay more consistent throughout the day rather than peak and dip due to long periods (fasting) between meals and that eating more frequently prevents feelings of intense hunger which leads to overeating.
Lastly, if one can lose weight by taking in less calories (and lower the calories taken in/ energy needs ratio) then increasing energy needs would also help with weight loss
Obviously, since you can't change how many calories your heart or brain need to funtion, the only way to do this is increase activity. Of course, that is through exercise.
Though there are many theories about what exercise is best, the fact remains that whatever the person will continue to do is the best exercise. If a person hates to run, then running isn't going to help because they'll give up. If money is an issue, joining a gym isn't a long term option either. They must find an activity that uses more energy than they take in.
Below is a link with some interesting calculaitons regarding how many calories must be cut back or expended in exercise to lose weight.
Hope this helps on your assignment.