Defining Obesity

The Centers for Disease Control and Prevention defines obesity as a range of weight that has been shown to increase the likelihood of certain diseases and conditions. These diseases are serious on their own, and when combined with obesity can cause a host of problems, including premature death.

Determining Obesity: Body Mass Index

Obesity is determined using a measure called body mass index (BMI). Your BMI is calculated by an equation that factors weight and height.

A normal BMI ranges from 18.5 to 24.9. A person with a BMI of 25 to 29.9 is considered overweight. A BMI of 30 or more is considered obese, with a 40-plus BMI classified as morbidly obese. As an example, a five-foot, seven-inch adult can weigh anywhere between 118 and 159 pounds and fall within the normal range.

It’s important to note that BMI does not measure body fat. An extremely muscular and fit person may register a high BMI and be very healthy. Although an important issue in determining whether a person is at risk for certain diseases, BMI is not the only factor considered.

Physicians also consider the following:

  • Diet
  • Physical activity
  • Blood pressure
  • Cholesterol
  • Body fat distribution (“apple-shape” versus “pear-shape”)

View the BMI chart

Determine your BMI with an interactive calculator. 

Causes of Obesity

Obesity is multifactorial disease—which means it has many causes. Simply eating too much and exercising too little do not cause obesity, although both play large parts in weight gain. Obesity is related to a variety of genetic, environmental and medical factors. For example, a person whose parents were obese is more likely to be obese than someone whose parents were normal weights. Additionally, obesity can cause or exacerbate a number of other medical conditions—called comorbidities—such as sleep apnea and high blood pressure.

Americans live an increasingly sedentary lifestyle. Few Americans get enough exercise—currently, the government recommends one hour every day. These low activities levels, in addition to many peoples’ reliance on convenient prepared foods that are often high in fat and low in nutritional value, are contributing factors to increasing rates of obesity.