I suppose its more of a personal choice than why they can do it.
I think by now, most of the population is aware that McDonalds and the entire fast food industry is going to add shit to your junk. No doubt about that. But even in my family, its a clear distinction of choice. I am a health freak, being incredibly obese as a child, i had dropped the fork and have been living as a very healthy teen ever since. True, my meals probably arent AS enjoyable as a nice butterly sirloin steak, or a giant bag of chips with some beer or soda. However, i get a different gratification of my self image. Now for some people, they dont give two shits about what they look like, but must have a good meal. I respect that as much as i respect having a good self image. Its all up to the person.
Now for SvnLyrBrto,
I may not be a trainer, but i have lost 60 pounds healthy in the matter of a couple of years.
Yes, true, exercizing (cardio and weights) will increase your basal metabolism by adding more muscle to your body and will burn more calories faster. However, because life is a bitch, eating the same as before isnt going to change much. You consequently might gain weight from the muscles you are gaining from your work out and fat from all the un metabolized foods in your system. This is bad for it puts pressure on your bones, for you may exceed a healthy range of muscle and fat for your body
My work out plan is simple andit works. Just try it out. Its hard, so maybe slowly adjust to it but here is mine.
Make sure your meals consist of...
Less than 2-3 servings of carbs (excess carbs are turned into glyocogen, at this stage, many left over foods in your body will turn into fat) and if possible limit carbs to only breakfast and lunch.
Eat plenty of vegitables 4-5 servings a day. Any time of the day is fine.
Eat lean protein, preferably chicken breast only if you are a body builder. Other lean meats work too but avoid fatty meats, or chicken skin. Terribly greasy.
Dont forget the legumes and nuts and dairy, but if possible eat low fat foods and dont over do the nuts and dairy, they are high in calories.
I personally havent touched any form of candy, or simple sugars such as sugar, syrup etc for a couple of years but this may seem like an impossible task so go ahead and let yourself go if you really must. Keep it at a minimum though. I dont suggest diet sodas either, they will kill you in a different way.
Now thats how you should eat, here is my simple meal guide.
Breakfast: Corn flakes, skim milk, some fruits and a low fat yougurt.
Lunch: Chicken breast (grilled) and vegitables
Dinner: Some sort of lean meat and vegitables.
Its not actually so bland once you mix it up a bit. Also when cooking avoid peanut, sunflower, palm oil. go for canola or olive.
The portions of your meal should be like a period. Your breakfast shoud be plentiful, for the breakfast runs your day's metabolism. Your lunch should be plentiful too, but dont gorge yourself. Your dinner should be light. Not too much pressure on the stomach..
Now regarding exercize.
Weight lift first
then cardio.
I dont know what kind of body type you wish to build, but whatever it is, try to exceed 45 minutes when exercizing. Thats when the real fat starts to burn if you keep exercizing consistantly, whether it be cardio or weight lifting.
You should weight lift first for it burns all the days carbs, and when the carbs deplete, your body will start to burn the fat (which you will be burning off by cardio)
Try to exercize everyday. It doesnt have to be 3 hours, but maybe an hour and a half each day. If you really cant, skip the weight lifting and go with just the cardio. Make sure you know you are pushing yourself. Lifting 2 10 lbs of dumbels and doing a lap isnt exercizing.
Lastly, after a good run or weight training, provide your body with some anti oxidants such as green tea, or some citrus fruits.
Hope this helps.