What is obesity?

Mrs. Marjorie Nolan Cohn
Nutrition & Dietetics Specialist

Obesity is a state of excess adipose tissue mass, or body fat. This condition usually translates into excessive body weight. On the one hand obesity can develop even in the absence of excessive body weight, whereas on the other hand a person (e.g., a body builder) can develop remarkable overweight without excessive body fatness. Meaning, ‘slim’ people can have a high fat mass and ‘overweight’ people (for their height) can have low fat mass. 

For adults, overweight and obesity ranges are determined by using weight and height to calculate a number called the "body mass index" (BMI). BMI is used because, for most people, it correlates with their amount of body fat.

According to the World Health Organization (WHO), obesity is classified as:

  • Class I for a BMI between 30 and 34.9 (moderate risk of mortality)
  • Class II for a BMI between 35 and 39.9 (high risk of mortality)
  • Class III for a BMI ≥ 40  (very high risk of mortality)
Dr. Michael T. Murray, ND
Naturopathic Medicine Specialist

Obesity is defined as a state of being more than 20 percent above "normal" weight or having a body fat percentage greater than 30 percent for women and 25 percent for men.

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Obesity refers to an abnormal and excessive amount of body fat. Most obese people are significantly overweight. However, obesity also occurs in people who are not overweight, but have more body fat than muscle. Obesity is considered a chronic illness. It is on the rise and is a risk factor for type 2 diabetes. Body mass index, skin fold measurements and bioelectrical impedance are common ways to assess obesity.

Dr. Dawn Marcus

Having a few extra pounds here and there is not obesity. Extra weight puts added stress on your heart and joints, but we’re not talking about a few love handles on most Americans. Obesity is generally considered to be having a weight that’s more than 20 percent above your ideal weight.

People who are obese have an abnormally high and unhealthy proportion of body fat. To measure obesity, researchers commonly use a formula based on weight and height known as the body mass index (BMI). BMI is the ratio of weight (in kilograms) to height (in meters) squared. BMI provides a more accurate measure of obesity or being overweight than does weight alone.

Compared with people in the healthy weight category, those who are overweight or obese are at greater risk for many diseases, including diabetes, high blood pressure, cardiovascular diseases, stroke and certain cancers. Obesity lowers life expectancy.

This answer is based on source information from the National Cancer Institute.

Obesity occurs when an individual has too much body fat because their calorie consumption is greater than what they burn in activity. Your amount of body fat is determined by a formula called the body mass index (BMI). Your BMI is calculated by dividing your weight in kilograms by your height in meters squared. A healthy BMI is anywhere from 18.5 to 24.9. If you are at 25 to 29.9, you are considered overweight. A score of 30 is considered obese, while 40 and higher is considered morbidly obese.

Obesity is a complex, misunderstood and mistreated disease, and with more than 30 percent of the United States adult population suffering from it, it has become the country's number one public health concern, according to the Centers for Disease Control and Prevention (CDC).

The World Health Organization (WHO) defines obesity as a disease in which excess fat is accumulated to an extent that health may be adversely affected. Measured by a person’s body mass index (BMI), a person is diagnosed as morbidly obese when his or her BMI is over 40. This presents significant health risks as well as opens the door for comorbid conditions such as type 2 diabetes, high blood pressure, heart disease, asthma and obstructive sleep apnea, among others. Morbid obesity is the second leading cause of preventable adult death in the United States, behind cigarette smoking.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.