Risk Factors:

Where you live plays a role in your risk for obesity. Simply living in the United States makes a person more susceptible to obesity. The prevalence of obesity in America has risen dramatically over the past few years and continues to increase.

• According to the latest figures available, 32.2% of American adults (aged 20 and older) are obese (BMI over 30) -- up from about 23% in the early 1990s.
• The number of Americans aged 20 - 74 who were overweight or obese also increased from about 44.8% in 1960 to 66.3% in 2004.

Fat tends to settle in certain regions, depending on gender. Women gain fat predominantly in the stomach, hips, and thighs, while men tend to gain fat in the belly and waist.

Risk by Age. People of any age are at risk for obesity. More children and adolescents are overweight in America than ever before. Gaining some weight is common with age, and adding about 10 pounds to a normal base weight over time is not harmful. The typical weight gain in American adults over 50, however, is worrisome. By age 55, the average American has added nearly 40 pounds of fat during the course of adulthood. This condition is made worse by the fact that muscle and bone mass decrease with age.

Risk 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. There are three high-risk periods for weight gain in women:

• The first is at the onset of menstruation, particularly if it is early.
• The second is after pregnancy, with higher risk for women who are already overweight.
• Finally, many women gain weight after menopause.

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

Risk by Economic Group. Obesity is more prevalent in lower economic groups. Low income women and their families tend to have fewer fruits and vegetables and are actually taking in more calories a day than higher-income women. However, obesity is increasing in young adults with college education as well as in other groups.

Ethnic Groups. Among ethnic groups in general, African-American women are more overweight than Caucasian women are, but African-American men are less obese than Caucasian men are. Hispanic men and women tend to weigh more than Caucasians.

US Regions. Regionally, the prevalence of obesity is lowest in the Western states and highest in the South.

Dietary Habits that Increase Risk

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

• Night-Eating Syndrome. Night-eating syndrome is defined as having no appetite in the morning, insomnia, and consuming more than half of the daily food intake after 6 p.m. It is associated with obesity and is difficult to treat. Stress reduction and relaxation techniques may be helpful.
• Binge Eating and Eating Disorders. About 30% of people who are obese are binge eaters who typically consume 5,000 - 15,000 calories in one sitting. To be diagnosed as a binge eater, a person has to binge at least twice a week for 6 months. Many experts believe that binge-eating carbohydrates causes an increase in a natural opiate, leading to dependence on carbohydrates. Therefore, this condition should be treated as an addiction. Other eating disorders are bulimia and anorexia. Bulimia is binge eating followed by purging in order to lose weight. A combined approach using behavioral therapy and antidepressants may help these individuals. [For more information, see In-Depth Report #49: Eating disorders.]
• Restrained Eating. Some people, mostly middle-aged women who have normal weight, follow a pattern called restrained eating. This pattern requires a high level of conscious control and usually maintains a lower weight. However, such restraint places these individuals at higher risk for loss of control and subsequent overeating.
• Infrequent Eating. Some evidence suggests that eating small frequent meals uses more calories than infrequent large meals. It should be strongly noted, however, that packaged snack foods add calories, and some do not produce a feeling of being full, so that people simply eat more than they should.

Specific Groups at Risk

Anyone with Sedentary Lifestyles. Office workers, drivers, and people who sit for long periods are at higher risk for obesity.

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 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 4 p.m. and 8 a.m.) tend to eat more and take longer naps than day workers, and they are more likely to gain excess weight.

People with Disabilities. Obesity rates are higher than average in people with physical or mental disabilities. Those with disabilities in the lower part of the body, such as the legs, are at highest risk.

People with Chronic Mental illnesses. People who have a chronic mental illness are at high risk for obesity and diabetes, most likely due to their lifestyle. In addition, many of the medications used to treat chronic mental illnesses can cause weight gain and increase the risk of diabetes.

Overweight Children: Special Considerations

Weight gain in children and adolescents is rising at an alarming rate. In 2004, 19% of young children aged 6 - 11 were overweight, an increase of 8% from 1994. Among children aged 2 - 5, 13.9% were overweight in 2004, up from 7.2% 10 years earlier.

Children and adolescents are considered to be overweight if their BMI is above 95% of the children in their age and sex categories. Ethnic variations, timing of growth spurts, and higher normal fat levels around puberty can affect these measurements.

Lifestyle Factors. Without educational or parental guidance, children are extremely vulnerable to the intense cultural pressures that are largely responsible for the obesity epidemic. The following are some specific problems created by the culture:

• Excessive television watching plays a critical role in obesity in children. Not only is it a sedentary activity, but television also offers innumerable temptations with its advertisements for fast foods, sugar cereals, and unhealthy snacks. Obesity rates increased in relation to the amount of time spent watching television
• Sugar, particularly from soda, other sweetened beverages, and fruit juice, may be the major contributor to childhood obesity. One study reported that drinking soda regularly increases a child's risk for obesity by 60%. The average American adolescent consumes 15 - 20 extra teaspoons of sugar a day just from soda and sugary drinks. (Juice, while better than soda, is still filled with sugar.)
• Less physical exercise and greater sedentary activities play another significant role in obesity in children. A high level of physical activity -- not just using up energy -- is important for weight control in young people. Unfortunately, according to one study, the annual distance walked by children has fallen by nearly 30% since 1972.Schools are also offering fewer opportunities for daily physical activities than in the past.

Neither the media nor the educational system has strong well-financed programs that encourage healthy alternatives, including exercise and healthy foods.

Family History. Parental obesity more than doubles the risk that a young child, whether thin or overweight, will become obese as an adult. In older children and teenagers, obesity in parents starts to count less as a predictor for body weight than their own weight. The risk for obesity may be due to environmental or genetic factors, or both.

Although some small studies have reported protection against obesity from breastfeeding, evidence is weak. Nevertheless, given the healthful effects of breastfeeding and the possibility that it may have even a slight impact on childhood obesity, it is highly recommended.

Biological Effect of Childhood Obesity on Adult Weight

Achieving a healthy weight becomes more difficult as children get older. The odds of obesity persisting into adulthood range from 20% in 4 year olds to 80% in teenagers. One reason for the persistence is biological. The fat cells change in number or mass depending on a person's age:

• Fat cells themselves multiply during two growth periods: early childhood and adolescence. Overeating during those times increases the number of fat cells. Some people are also just born with more fat cells.
• After adolescence, fat cells tend to increase in mass rather than quantity, so that adults who overeat and gain weight tend to have larger fat cells, not more of them. This growth in mass may be responsible for the greater risk of persistent obesity among teenagers compared to small children who are overweight. Losing weight after adolescence reduces the size of the fat cells but not their number, so weight loss becomes much more difficult.