Some people manage to modify their weight through effective lifestyle change, but many turn repeatedly to drastic, short-term, and ultimately ineffectual weight loss methods or to self-inflicted serious semi-starvation with its attendant negative physical and psychological consequences.
—Joel Yaeger, M.D., Department of Psychiatry, University of New Mexico School of Medicine, in "Weighty Perspectives: Contemporary Challenges in Obesity and Eating Disorders," American Journal of Psychiatry, vol. 157, no. 6, June 2000
One of the challenges facing public-health professionals as they seek to combat obesity among Americans is helping consumers to distinguish myths, lore, legends, and outright fraud from accurate, usable information about nutrition, diet, exercise, and weight loss. Some of these inaccuracies are so longstanding and deeply rooted in American culture that even the most educated consumers unquestioningly accept them as facts. Others began with a kernel of truth but have been so wildly distorted or misinterpreted that they are confusing, misleading, or entirely erroneous. The rapid influx and dissemination of information about the origins of overweight and obesity and conflicting accounts of how best to treat these problems compound the challenge. With media reports and advertisements trumpeting different diets nearly every week, it is no wonder that Americans are confused about diet and weight loss.
The fiction that people who are overweight or obese are lazy and weak-willed is among the most harmful myths because it serves to promote stigma, bias, and discrimination. Another common misconception is that it is equally easy or difficult for all people to lose weight. There are biological and behavioral factors that affect an individual's body weight, and people vary in terms of genetic propensity to become overweight, basal metabolic rate (BMR), and number of fat cells. BMR, often referred to simply as "metabolic rate," is the number of calories an individual expends at rest to maintain normal body functions. BMR changes with age, weight, height, gender, diet, and exercise habits and has been found to vary by as much as 1,000 calories a day. Differences in metabolic rate explain, in part, why not all people who adhere to the same diet achieve the same results in terms of pounds lost or rate of weight loss. Another factor that produces variation in weight loss is the number of fat cells in the dieter's body. Although fat cells do not determine body weight, they are affected by weight gain and act to limit weight loss since their number cannot be decreased. For example, a normal-weight person has about forty billion fat cells while an individual who weighs 250 pounds with a body mass index (BMI) of 40 may have as many as 100 billion fat cells. Weight loss causes fat cells to shrink in size but does not decrease their number. As a result, individuals with twice as many fat cells as normal-weight people may be able to shrink their fat cells to a normal size but even when they have attained a healthy weight will still have twice as many fat cells.