In pursuit of making the treatment of obesity more of a science, my colleagues and I tried to establish principles for an appropriate rate of weight loss. Earlier research in body composition studies by Dr. John Garrow of St. Bart’s Hospital, London, England, found that the composition of excess weight in the obese individual is about 75 percent fat and 25 percent fat-free mass (the non-fat constituents of the body including muscle). This led us to determine that an appropriate rate of weight loss was a rate at which at least 75 percent fat and no more than 25 percent fat-free mass is lost.
One pound of body weight of acceptable composition (75 percent fat and 25 percent fat-free mass) is equal to an energy deficit of about 3200 calories. Therefore, if an individual in a weight loss program continues to lose more than a pound of weight for every 3200-calorie deficit, the lost weight is very likely to be higher in fat-free mass and lower in fat mass than is healthy and desirable. This reasoning assumes that the individual is not becoming dehydrated (i.e., is not losing excess water).
The more rapid the rate of weight loss, the more probable the proportion of fat-free mass (much of which consists of body protein) will exceed the 25 percent limit. When continued for a prolonged period of time, such unduly rapid weight loss can result in serious depletion of body protein. Depletion of body protein will cause weakness, apathy, loss of immunity, poor wound healing, and many other adverse effects.