The reason why we're the most obese nation on the planet is simple -- Americans eat too many calories, way in excess of their daily energy needs, and too many of those calories are "empty" calories. The empty calories, composed primarily of sugars like sucrose, glucose, and lactose, are turned into glycogen in our livers and then must be immediately "burned" by the energy demands of our muscles. There's the problem -- that isn't happening, for the most part. People eat too much, then move too little.
The average caloric intake of a typically obese person would probably be a bit too much for a person who was going to spend the day working as a steveadore. However, when that caloric intake just spends the day behind a desk, or on a couch, then what becomes of it is that it is stored in newly-created fat cells -- hopefully for future use -- which also usually never happens. Those fat cells eventually reach a stage of maturity where they are actually no longer able to give up their energy-- and the blood then becomes saturated with dangerous low-density lipoprotiens and serum cholesterol. These fats build up in mass areas along the lining of our arteries, which become less flexible as the "plaque" hardens. Blood flow to critical organs like the heart muscles, brain, and kidneys is reduced, and eventually results in heart attacks, strokes, and renal failure.
There really is only one way to avoid these problems -- make sure you are burning (metabolizing) the calories you're taking in, and make sure you're not taking in more calories than you're burning.
The American addiction to oral pleasure -- in the form of food, alcohol, and tobacco, is probably our greatest problem. Another is that we eat junk because our culture doesn't allow us enough time each day to eat proper meals at proper times. Until this changes, Americans will be fat. I'm a more or less normal weight for a male my age, and I have to sacrifice a lot of eating pleasure to maintain my weight. I'd love nothing more than to sit down to a nice big plate of pasta every evening before going to bed, but I don't. Since I have to retire early (usually 8 PM) to get up early enough to be at work by 6 AM, my evening meal often consists of a glass of Ovaltine and some raw carrots. I have my main meal at lunchtime, which is 11 AM since I'm eating breakfast at 3:30 AM.
I've had to make some serious lifestyle adaptations in order to maintain a healthy weight, including the fact that I'm now riding my bike to work nearly every day. Most Americans, even those who live as close to work as I do, won't do that.
