Our weight is calculated by multiplying our body mass by the gravity of the earth. Therefore, our weight is less on the moon than on earth, becuse the gravity is less on the moon. Our mass, is, however, the part that we can control while here on earth. What we eat each day has a great deal to do with our mass. Basically, we gain mass when our daily intake of food is more than our daily burning of energy. Over several years of time, if we keep eating more than we need for energy, we gain more and more weight. Our body is very efficiant at getting its energy from food. The body stores any unwanted energy, but never wastes a great deal of valuable nutrition. We can gain mass by fat, protein, or both.
Getting fat means that our body mass is increasing, and this increase is in form of fat, and not so much protein. When we eat too much food, our body stores unwanted food in form of fat. This means that it does not make a difference in whether we eat too much fat, or to much sugar. Everything gets converted to fat before it is stored. There is a good reason for this. Energy is stored by the body, so it can be used when the body is startving, or not getting enough nutritions. For every one gram of stroed fat that is used, the body gets 9 calories. (kcal) If the body stored the food as sugars or proteins, it would only get 4 calories when it burned them. Therefore, in the interest of efficiency, the body stores food as fat.
What makes us gain weight is the extra calories. If we cut down on fat, but then increase our intake of sugars, we have not improved our eating much. One example of this is when people are eating the olestra containing potato chips instead of the regular kind. Now, they think that they can eat a whole bag without gaining weight. Not to mention my objection to olestra as physician, the problem is that you are simply exchanging fat calories for carbohydrate calories. As I said to you earlier, the sugar will just get converted to fat, and we end up back where we are. So, it is better to cut down on calories, than to cut down on fat.
There are several reasons. For one thing, some people may eat more on some social occasions, but on a day to day basis, they don't eat as much. Another reason is that some people's metabolic rate is higher. This has to do with the function of the thyroid gland. This means that they burn more energy, on average, in order to do their activities. Funny enough, the people who burn less energy are more efficient in energy use, which is why they have more leftover, and end up storing more. Another reason is that some poeple excercise more, and have a more active lifestyle.