第10章感情と動機づけ

When someone weighs more than what is generally accepted as healthy for a given height, they are considered overweight or obese. According to the Centers for Disease Control and Prevention (CDC), an adult with a body mass index (BMI) between 25 and 29.9 is considered overweight (Figure 10.10). An adult with a BMI of 30 or higher is considered obese (Centers for Disease Control and Prevention [CDC], 2012). People who are so overweight that they are at risk for death are classified as severely obese. Severe obesity is defined as having a BMI over 40. Note that although BMI has been used as a healthy weight indicator by the World Health Organization (WHO), the CDC, and other groups, its value as an assessment tool has been questioned. The BMI is most useful for studying populations, which is the work of these organizations. It is less useful in assessing an individual since height and weight measurements fail to account for important factors like fitness level. An athlete, for example, may have a high BMI because the tool doesn’t distinguish between the body’s percentage of fat and muscle in a person’s weight. BMI scales have not accounted for differences in body composition related to race or ethnicity; as a result, BMI is less useful in determining health of all people. While many healthcare professionals and organizations still utilize BMI, the American Medical Association in 2023 recommended that it be removed as a standard measure of health.

Being extremely overweight or obese is a risk factor for several negative health consequences. These include, but are not limited to, an increased risk for cardiovascular disease, stroke, Type 2 diabetes, liver disease, sleep apnea, colon cancer, breast cancer, infertility, and arthritis. Given that it is estimated that in the United States around forty percent of the adult population is obese and that nearly three-quarters of adults and one in six children qualify as overweight (CDC, 2018), there is substantial interest in trying to understand how to combat this important public health concern.

What causes someone to be overweight or obese? You have already read that both genes and environment are important factors for determining body weight, and if more calories are consumed than expended, excess energy is stored as fat. However, socioeconomic status and the physical environment must also be considered as contributing factors (CDC, 2012). For example, an individual who lives in a neighborhood with high crime rates and few food options may never feel comfortable walking or biking to work or to the local market. This might limit the amount of physical activity in which they engage. Similarly, some people may not be able to afford healthy food options from their market, or these options may be unavailable (especially in urban areas or poorer neighborhoods); therefore, some people must rely primarily on available, inexpensive, high fat, and high calorie fast food as their primary source of nutrition.

Generally, people are encouraged to try to maintain and improve health through a combination of both diet and exercise. While some people are very successful with these approaches, many are not. In cases in which a person has had no success with repeated attempts to reduce weight or is at risk for death because of obesity, bariatric surgery may be recommended. Bariatric surgery is a type of surgery specifically aimed at weight reduction, and it involves modifying the gastrointestinal system to reduce the amount of food that can be eaten and/or limiting how much of the digested food can be absorbed (Figure 10.11) (Mayo Clinic, 2013). A recent meta-analysis suggests that bariatric surgery is more effective than non-surgical treatment for obesity in the two-years immediately following the procedure, but to date, no long-term studies yet exist (Gloy et al., 2013).