You may have heard that one pound of fat holds about 3,500 calories and that, to lose that pound of fat, you need to eat 3,500 calories less than you burn over some period of time. This formula is truly the cornerstone of weight management and has been for decades.
Unfortunately, things are a bit messier in the real world than this simple equation would lead you to think.
First, when you restrict calories to a level well below your metabolic needs, your body will attempt to adapt its metabolism to the newly reduced intake. That is, you will feel sluggish, move less, and a number of metabolic activities will go into a lower gear; reducing your caloric needs by as much as 30%. Severe caloric restriction is thus not only very difficult to endure, it also is likely to produce less weight loss than you hope.
The second factor affecting the nature of weight loss is that the content of your diet may affect what kind of tissue is lost. If you eat too little protein, for example, and you will tend to shed lean body weight: always a really bad idea. But lean body weight also yields fewer calories per pound: only about 600 calories. So lean body is used up more quickly than fat – but such losses come at very high risk to your overall health. In the end, your actual weight loss is not likely to be exactly 1 pound for each 3,500 calories that you eliminate from your diet. Only if you approach weight loss by moderately reducing calories, staying active, and eating a balanced diet with enough protein will you come close to the predicted pound of weight loss per 3,500 calories.
The research of Dr. Kevin D. Hall at the National Institutes of Health has revealed a number of other interesting facts about how caloric restriction interacts with metabolism. Dr. Hall has found that not only does the content of your diet affect the type of tissue lost, but that your starting body composition and level of calorie restriction do as well. For example, if you have significant bodyfat stores, your body will tend to give up the fat before working on lean tissue. As you lose weight and come closer to your ideal weight, the amount of lean body tissue given up will start to rise. This is one reason why it is progressively harder to lose bodyfat as you get closer to your ideal weight: your body will begin using lean sources more than it did when you had more fat to spare. The take-away here is that if you have a lot of bodyfat to lose, you can be a bit more aggressive with your calorie restriction. However, as you get closer to your ideal weight, it makes no sense to maintain a state of semi-starvation. Not only will this begin to damage lean tissue, it is also likely to induce psychological effects such as depression and hypochondriasis.
The next thing to consider is that as you lose weight, your body’s metabolic needs will go down. Even though the vast majority of fat on your body isn’t very metabolically active, you burn fewer calories when you lighter simply because you need less energy to move. Thus, you’ll want to re-scale your diet periodically as you make progress with weight loss.
Speaking of Metabolic Rate
The Motivation Alliance now permits you to estimate your daily caloric burn rate and to see how it stacks up against your dietary intake. Better yet, we’ve gone beyond the simple equations that you’ll find in most programs to provide a much closer estimate of your actual metabolic rate. The page will also capture important information about your diet – if you have been logging it – including total calories, macronutrient balance and the appropriate modifications to meet your weight loss or gain goals. To try out the new page, simply visit the “Metabolic and Caloric Balance” page using the button by the same name in the “Junk Food Averse” area.