Americans trying to lose weight have plenty of company. As per a 1995 report from the Institute of Medicine (IOM), tens of millions of Americans are dieting at any given time, spending more than $33 billion yearly on weight-reduction products, such as diet foods and drinks.

Yet, studies over the last two decades by the National Center for Health Statistics show that obesity in the United States is actually on the rise. Today, approximately 35 percent of women and 31 percent of men age 20 and older are considered obese, up from approximately 30 percent and 25 percent, respectively, in 1980.

The words obesity and overweight are generally used interchangeably. However, as per the IOM report, their technical meanings are not identical. Overweight refers to an excess of body weight that includes all tissues, such as fat, bone and muscle. Obesity refers specifically to an excess of body fat. It is possible to be overweight without being obese, as in the case of a body builder who has a substantial amount of muscle mass. It is possible to be obese without being overweight, as in the case of a very sedentary person who is within the desirable weight range but who nevertheless has an excess of body fat. However, most overweight people are also obese and vice versa. Men with more than 25 percent and women with more than 30 percent body fat are considered obese.

A number of people who diet fail to lose weight--or, if they do lose, fail to maintain the lower weight over the long term. As the IOM report, "Weighing The Options: Criteria for Evaluating Weight-Management Programs," points out, obesity is "a complex, multifactorial disease of appetite regulation and energy metabolism."

Because a number of factors affect how much or how little food a person eats and how that food is metabolized, or processed, by the body, losing weight is not simple. For example, recent studies suggest a role for genetic makeup in obesity. This area is still controversial, and more studies will be needed before researchers can say with certainty that a person's genes may set limits on how much weight can be lost and maintained.

Yet a number of people persist in seeking simple cures to this complex health problem. Lured by fad diets or pills that promise a quick and easy path to thinness, they end up disappointed when they regain lost weight.

---