The World Health Organization now considers obesity to be a global epidemic and a public health problem as more nations become “Westernized.” Globally, an estimated 250 million adults are now obese, and many more are overweight.

Obesity in American Adults
The prevalence of obesity (defined as a BMI of over 30) in the United States has risen dramatically over the past few years. It is now estimated that 61% of Americans are now overweight, up from 43% in the early 1940s. And according to a 2001 study, nearly 20% of American adults are obese (BMI over 30). Regionally, the prevalence of obesity is lowest in the Western states (13.8% in Colorado) and highest in the South (24% in Mississippi).

Gaining some weight is inevitable with age and adding about 10 pounds to a normal base weight over time is not harmful. The weight gain in American adults over 50, however, is significant, with 64% of women and 73% of men being seriously overweight. This condition is made worse by the fact that muscle and bone mass decrease with age, so the fat increase is actually about one and a half pounds. Some studies suggest that by age 55, the average American has added over 37 pounds of fat during the course of adulthood.

Obesity by Ethnic, Social, and Income Groups
Obesity is more prevalent in lower economic groups but it appears to be increasing in young adults with some college education. Obesity, in fact, has increased in every state, in both men and women, across all age groups, and in every ethnic group. Among ethnic groups, African American women are more overweight than Caucasian women but African American men are less obese than Caucasian men. Hispanic men and women tend to weigh more than Caucasians.

Weight Gain by Gender
In men, BMI tends to increase until age 50 and then it levels off; in women, weight tends to increase until age 70 before it plateaus. A 2000 study has found that there are three high-risk periods for weight gain in women.

 
• The first is at the onset of menstruation, particularly if it is early. (It should also be noted, that obesity in childhood may actually be a contributor to early puberty, which in turn increases the risk for more weight gain.)  
• The second is after pregnancy, with higher risk for women who are already overweight.  
• Finally, many women tend to gain weight after menopause.

These findings are significant because they may allow women to target high-risk times, and consequently prevent unnecessary weight gain.

Obesity in Children
More children and adolescents are overweight in America than ever before. According to a 2001 report based on a study of 8,000 children, the rate of overweight children among African-American and Hispanics increased by more than 120% and among Caucasian children by 50% between 1986 and 1998. In the study, 22% of African-American and Hispanic children were overweight, while about 12% of Caucasian children were overweight. Other studies have estimated that about 35% of children were either at risk for being overweight or are overweight. And the problem is becoming global.

Dietary Habits
A number of dietary habits put people at risk for becoming overweight:

 
• Night-Eating. Consuming between 25% and 50% of daily calories between the evening meal and the next morning is referred to as night-eating syndrome and is associated with obesity.  
• Binge Eating and Eating Disorders. About 30% of people who are obese are binge-eaters who typically consume 5,000 to 15,000 calories in one sitting. To be diagnosed as a binge eater, a person has to binge at least twice a week for six months. Many experts believe that binge-eating carbohydrates causes an increase in a natural opiate leading to dependence on carbohydrates, and, therefore, the condition should be treated as an addiction. Dangerous consequences of binge eating are its antitheses, the eating disorders bulimia and anorexia. Bulimia is binge-eating followed by purging in order to lose weight. Anorexia Nervosa is a mental illness in which the person refuses to maintain weight at the normal level because of a terrible fear of getting fat and an abnormal perception of what his or her body looks like. Both conditions pose risks for serious medical problems, and anorexia nervosa can be life threatening.  
• Restrained Eating. Some people, mostly middle-aged women who have normal weight, have a pattern referred to as restrained eating. This pattern requires a high level of conscious control and usually maintains a lower weight. However, such restrain places these individuals at higher risk for loss of control and subsequent overeating.  
• Infrequent Eating. There is some evidence to suggest that eating small frequent meals uses more calories than infrequent large meals.

Specific Groups at Risk
Ex-Smokers. The trend toward weight increase has followed the trend for quitting smoking. Nicotine increases the metabolic rate, and quitting, even without eating more, can cause a weight gain, which may be considerable. It is important to note that weight control is not a valid reason to smoke. People in previous centuries did not smoke cigarettes, nor were they usually obese.

Shift-Workers. A recent study found that individuals who work late shifts (between 4PM and 8AM) tend to eat more and take longer naps than day workers and are more likely to gain excess weight.