The mantra for a long time has been "exercise more", etc. Problem is when people are heavy, they end up hurting themselves. People get into shape fairly quickly(not in the clinical setting, BTW) almost exclusively through diet. Basically, our diets are complete crap in the US (and most other western countries)
The most critical thing we can change is to stop eating "fast" (think white and grain based) carbohydrates. Simply, our bodies don't really "need" to eat fast carbs, especially not those types. We use glucose for energy, yes. Our brain runs on it. That is why we have gluconeogenisis, so we never run out. People seem to get fat over insulin and cortisol issues, much more so than actual dietary fats. (see the masai or inuit who eat 90% meat, milk, blubber, cows blood, etc). Even more interesting is research showing cholesterol problems clear up when you manipulate the carbs in the diet more than the protein/fats. Also, nearly everyone has a grain allergy of some degree. Grains are built to resist digestion. Inflammed bowels hinder absorption, kick out lots of bad stuff, effect other parts of our bodies, etc..
You can never completely remove all refined carbs here in the US, for example, but you can get close. It takes will, and tenacity. It takes patience, and it takes effort to cook most your meals.
I follow a "paleo" type diet that essentially eliminates grains and starchy carbs and fruits from my diet. I am left with meat/ proteins, low sugar vegetables (think peppers, celery, radishes, artichokes, tomatoes, etc) to cover most of my diet. You can actually make an amazing number of dishes with some creative brainstorming.
Anyone interested should look into these things more. I am no dietician, YMMV. Weight kinda falls off easy when you are doing the right thing.