Hunger and Eating: Learn It 2—Obesity

Obesity

When someone weighs more than what is generally considered to be healthy for a given height, they are considered by medical professionals to be overweight or obese. Historically, body weight and obesity has been assessed via the body mass index (BMI).

body mass index (BMI)

The body mass index (BMI) is a widely used measurement system for assessing whether an individual’s weight is healthy for their height. It is calculated by dividing an individual’s weight in kilograms by their height in meters squared.

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.
  • An adult with a BMI of 30 or higher is considered obese.
  • People who are so overweight that they are at risk for death are classified as morbidly obese. Severe, or morbid, obesity is defined as having a BMI over 40.
A BMI chart showing weight and height as it corresponds with being underweight, in the normal range, overweight, or obese. For example, someone who is 5 foot 7 and under 120 lbs would be underweight, in the normal range through 155 lbs, overweight until 180 lbs, and obese beyond that.
Figure 1. This chart is used to correlate weight and height with body mass index.
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 such as body composition (muscle mass versus fat), location of body fat, and lifestyle behaviors.

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 one-third of the adult population is obese and that nearly two-thirds of adults and one in six children qualify as overweight (CDC, 2012), there is substantial interest in trying to understand how to combat this important public health concern.

Causes of Obesity

What causes someone to be overweight or obese? Both genetics and lifestyle 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 can also be considered contributing factors (CDC, 2012). For example, an individual who lives in an impoverished neighborhood or one that is unsafe 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 and result in an increased body weight. 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 rely primarily on inexpensive, high-fat, and high-calorie fast food as their primary source of nutrition.

An illustration depicts a gastric band wrapped around the top portion of a stomach. A bulging area directly above the gastric band is labeled “Small stomach pouch.” The area directly below the stomach is labeled “Duodenum.” Down-facing arrows indicate the direction in which digested food travels from the esophagus at the top, down through the stomach, and into the duodenum.
Figure 2. Gastric banding surgery creates a small pouch of stomach, reducing the size of the stomach that can be used for digestion.

Weight Loss

Generally, overweight and obese individuals are encouraged to try to reduce their weight through a combination of both diet and exercise. While some people are very successful with these approaches, many struggle to lose excess weight. 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 (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).

A painting shows Eugenia Martínez Vallejo.
Figure 3. Eugenia Martínez Vallejo, depicted in this 1680 painting, may have had Prader-Willi syndrome. At just eight years old, she weighed approximately 120 pounds, and she was nicknamed “La Monstrua” (the monster).

Prader-Willi Syndrome (PWS) is a genetic disorder that results in persistent feelings of intense hunger and reduced rates of metabolism. Typically, affected children have to be supervised around the clock to ensure that they do not engage in excessive eating. Currently, PWS is the leading genetic cause of morbid obesity in children, and it is associated with a number of cognitive deficits and emotional problems.

While genetic testing can be used to make a diagnosis, there are a number of behavioral diagnostic criteria associated with PWS. From birth to 2 years of age, a lack of muscle tone and poor sucking behavior may serve as early signs of PWS. Developmental delays are seen between the ages of 6 and 12, and excessive eating and cognitive deficits associated with PWS usually onset a little later.

While the exact mechanisms of PWS are not fully understood, there is evidence that affected individuals have hypothalamic abnormalities. This is not surprising, given the hypothalamus’s role in regulating hunger and eating. However, as you will learn in the next section of this module, the hypothalamus is also involved in the regulation of sexual behavior. Consequently, many individuals suffering from PWS fail to reach sexual maturity during adolescence.

There is no current treatment or cure for PWS. However, if weight can be controlled in these individuals, then their life expectancies are significantly increased (historically, sufferers of PWS often died in adolescence or early adulthood). Advances in the use of various psychoactive medications and growth hormones continue to enhance the quality of life for individuals with PWS (Cassidy & Driscoll, 2009; Prader-Willi Syndrome Association, 2012).

Review the information presented above in the following interactive: