Body Weight Simulator bwsimulator.­niddk.­nih.­gov


Background on the Body Weight Simulator: Losing Weight is Hard

Anyone who has ever tried losing weight knows that cutting calories doesn't work nearly as well as conventional wisdom suggests. The classical math of energy balance says that one pound of fat whether it's on the plate or on the body contains about 3500 calories. This classical math is valid and the body weight simulator neither changes nor challenges this. 

The problem with the classical math of energy balance is that it has been misused by extrapolating calorie content to weight loss. In other words, it has been misused by saying that SINCE a pound of fat on the body contains about 3,500 calories, all a person must do to lose that pound of fat is consume 3,500 less that normal. For example, according to this idea, if your weight is stable, neither rising nor falling and you want to lose a pound of fat, the conventional thinking argues that you merely need to reduce your daily calorie intake by 100 calories and in 35 days (35 x 100 = 3,500) you should have a pound less body fat and in a year you should have about 11 pounds less. The problem of course is that it doesn't work that way in the real world. The body ADAPTS to weight loss by reducing its metabolism. How MUCH the body reduces its metabolism and how this affects real world weight loss, these are the issues that the the body weight simulator addresses. THIS is the breakthrough.

Understanding the NIH Body Weight Simulator's Underlying Equation:

Rate of weight loss is related to weight LOST through a differential equation. That is to say that rate of weight loss is NOT a linear function. The more weight a human body loses, the more significantly does its basal metabolic rate slow so that rate of weight loss decreases over time. Still, as the java-script application demonstrates, rate of weight loss generally does not reach zero even for a modest chronic caloric deficit; it merely decreases. The equation itself is shown below:

The derivation is laudatory. The idea is old and unsurprising. Whether because of "thrifty" genes or some alternative teleology, humans, probably all mammals, perhaps all vertebrates, tend to respond to reduced food intake with reduced metabolic rate.

The body weight simulator is a Java-script widget that is based upon the "new weight loss math" that accounts for metabolic adaptation to caloric restriction.