Coverage of obesity in the popular press has reached a fever pitch in recent years. By far, the most common definition of obesity uses the body mass index (BMI) to determine who is overweight or obese. A person's BMI is a ratio of his or her weight to height. Many times BMI is criticized for the false positives, where very muscular people are deemed to be obese despite ultralow body fat levels. Waist circumference or waist-to-hip ratio (WHR) measures something called “abdominal or central obesity”, a condition that is closely related to negative health outcomes such as cardiovascular disease. The costs to society of obesity and related health issues are tremendous. Women, ethnic and racial subgroups, and those of low socioeconomic status (SES) all display higher rates of obesity than the overall population. Obesity is much more common in certain racial and ethnic subpopulations, as compared with Caucasian Americans.

The genetic causes of obesity are often separated into to two types: monogenic and polygenic. Monogenic obesity refers to forms of obesity that result from very rare mutations in single genes. In the case of polygenic obesity, any single gene susceptibility would have a very small effect, but taken together, the cumulative effect of several susceptibilities leads to a substantially increased risk of obesity. There are many other pieces of compelling evidence for the environmental causes of obesity. The prevalence of obesity in the United States has been the highest in the world, though the prevalence of obesity is rising in both developed and developing nations around the globe as they adopt “Western” lifestyles of decreased physical activity and higher consumption of cheap, calorie-dense foods. There is another theory that “genetic drift” and “predation release” caused obesity to simply become neutral to our ancestors, as opposed to detrimental.

Most school-based interventions aimed at preventing obesity have focused on a few key areas: improving the food offered in school, increasing opportunities for physical activity, health and nutrition education curricula, and screening youth for overweight and obesity. Positive effects on physical activity are encouraging because developing good habits early may help prevent obesity later in life. Many obesity prevention programs have looked at adding health, nutrition, and physical education courses to the school day. One initiative that has been proposed is to screen children and teens for obesity in schools, similar to the hearing and vision screenings that already take place. Some schools also collect body mass index (BMI) data on students for surveillance purposes, where information is anonymous and used to track whether certain school policies are effective in reducing rates of obesity for the school, district, or state as a whole.

Generally speaking, there are various levels of intensity for obesity treatment. Self-initiated diets and commercial programs are typically the first step, and individuals may cycle through dozens of these diets before seeking more intensive treatments. Lifestyle or behavior modification programs are typically the next line of defense, which may include modifying eating behavior or dieting, exercise, and modifying other behaviors under professional guidance. The third level of intensity consists of medical treatment, such as prescription medication, or a combination of lifestyle modification and medication. Surgery is often a last resort for treatment for severely obese individuals with comorbidities. In revisiting the issue of weight-loss expectations, it seems that surgery is the only treatment that would allow obese individuals to meet their weight-loss goals. Few guidelines are available when it comes to the use of medication for obesity treatment among children and adolescents.

This chapter discusses the various medical problems associated with obesity among children and adults, as well as the long-term medical consequences of obesity. Throughout the history of mankind, various methods of addressing obesity have been documented. Physicians began to recognize the association between obesity and various other disorders or conditions, including shortness of breath, diabetes, coronary heart disease (CHD), lethargy, depression, ulcers, sleep apnea, and poor circulation. The link between obesity and related diseases and risk factors, however, is not wholly consistent across the life span. Longitudinal studies have found that obesity is related to heightened risk of CHD, heart attacks, and cardiovascular disease mortality in older men, but not necessarily in older women. Childhood obesity is also associated with increased risk of CHD in adulthood. Obese children's risk of hypertension is three times higher when compared with normal-weight peers regardless of race, gender, and age.

This chapter describes how overweight and obesity are defined or measured, most commonly with the body mass index (BMI), which is derived from a formula using height and weight only. People who are obese are more likely to suffer from a variety of negative health consequences-medical, psychological, and social in nature. On an individual level, genes are hugely important in determining why one person is obese, whereas his neighbor is stick-thin. Everything from school lunches to soda advertisements to the distance to the nearest park has been implicated in raising the risk of obesity. One controversy that receives a lot of attention is whether to blame poorer diet or lower activity level for societal increases in obesity. Although obesity has become a problem in many different countries across the globe, there are several differences in the pattern of who becomes obese.

This chapter discusses theories related to how social groups may promote the transmission of obesity. Some attention should be given to changes in perceptions of obesity, rather than simply changes in actual rates of objective measures of obesity, in part due to the role that social perception plays in actual psychological and social responses to obesity. Whereas many medical and physical consequences of obesity are more directly related to the physiological dangers of excess body weight, many social and psychological consequences of obesity are related to the perceptions of others. Prejudice against obesity is considered as common as racial prejudice. It’s important to note that there can be numerous moderator variables that contribute to the relationship between obesity and depression, such as having an under-active thyroid, which has been associated with both obesity and depression. The chapter also discusses eating disorders, attention deficit/hyperactivity disorder, sexual dysfunction, and other psychopathological disorders.