In order to lose weight and maintain that loss in the long-run, you must first understand that the key to weight loss is simply a net loss of calories. Weight gain is generally a result of consuming more calories than your body spends. In other words, your weight is a direct result of the amount of calories you put into it.

Calories are energy for your body much like gas is fuel for a car; your body requires a certain number of calories to work just like your car requires a certain amount of gas to run. The difference is that if you put too much gas in your car, the gas would simply run out of the tank and pour out onto the ground, whereas if you put more calories into your body than it needs, it stores those extra calories as fat. Your body was created to survive so that if faced with a famine or shortage in food supply, you would have the ability to use those fat stores for energy. Fortunately (or unfortunately), in America, most of us have access to an abundance of food, so very few of us would ever need to call upon our fat stores to save us from starvation. So, as we pour in unnecessary calories without burning them in physical activity, our bodies become fatter. The goal in weight loss, therefore, is to achieve a net loss of calories by consuming fewer calories in the foods we choose and spending more calories in physical activity.

If you liken the concept of weight loss to a "fat" bank account that you are trying to empty, think of calories as money. The only way to lessen the money in your bank account is to either put less in or take more out. I would suggest both. In other words, you will need to start putting fewer calories into your body and start spending more calories in regular physical activity. It takes a net loss of 3500 calories to lose a pound of fat, whether that net loss is achieved by cutting caloric intake or by increasing calories spent in physical activity. For example, if you were to cut 300 unnecessary calories per day from your diet and spend an extra 200 calories in activity (a total of 500 calories per day), you would lose approximately 1 pound per week (500 calories per day times 7 days per week).

You may be wondering how many calories you should be eating in a day. You may also be thinking that if the key to weight loss is simply a net loss in calories, why not cut way back and follow a very low-calorie diet with 800 or 1000 calories per day? For one, following a very low-calorie diet is a quick-fix weight loss method and one that you cannot maintain long-term. Also, when you go from a high calorie diet, such as 3500 calories or more per day down to 1000 calories per day, your body assumes that you must be facing a famine and potential starvation, so it lowers your metabolism to conserve energy as long as possible.

Also consider that if you currently consume 3500 calories per day and you cut back to 2500, you will (theoretically) lose 2 pounds per week (a net loss of 1000 calories per day x 7 days per week = 7000 calories, divided by 3500 calories per pound of fat = 2 pounds of fat per week). All you need to do is cut out 500-1000 unnecessary calories from your current diet in order to lose 1-2 pounds per week. That's much less painful than trying to follow an impossibly restrictive low-calorie diet.