What is body mass index (BMI)?

One of the most common topics patients talk about with their doctors is weight loss. One-third of Americans today are overweight, which can be caused by a variety of factors. Doctors now see excess weight as an important, treatable medical condition and work with patients to get to their healthy body weight.

Body weight can be measured in several ways. One of the most popular methods that show whether or not a person is overweight is the body mass index (BMI).

Body mass index (BMI) is calculated by dividing a person's weight (in kilograms) by his or her height (in meters, squared). BMI can also be calculated by multiplying weight (in pounds) by 703, then dividing by height (in inches, squared). People with BMIs of 25 and above are considered to be overweight. (Many people do a quick BMI calculation online.)

There are exceptions. Though body mass index is a good indicator of overweight or obesity, BMI may not apply equally to everyone. For example, bodybuilders and other athletes may have a higher BMI due to muscle mass, even though they're not necessarily overweight.

Another measurement is waist circumference, which can show body fat distribution. Too much belly fat may place you at higher risk for health problems related to obesity. Men with waistlines whose waist circumference is above 40 inches and non-pregnant women’s waistlines above 35 inches have higher risk of obesity-related conditions.

The chart below shows some examples of body mass indexes. The figure at which your height corresponds with your weight is your body mass index. BMI is classified as the following:

  • BMI under 18.5 is underweight
  • BMI 18.5 to 24.9 is healthy
  • BMI 25.0 to 29.9 is overweight
  • BMI 30.0 to 39.9 is obese

Having a BMI over 30 places you at risk for developing obesity-related medical conditions such as diabetes, high blood pressure and coronary artery disease. A BMI over 40 indicates that a person is morbidly obese (more than 100 pounds over ideal body weight, increasing the chance of serious health problems).

Body mass by height and weight

Body Mass Index Chart

Does being overweight lead to any medical risks?

The best reason to attain and maintain your ideal weight is to reduce or eliminate medical problems that are more likely to occur with increasing weight. These conditions include high blood pressure, coronary artery disease, type 2 diabetes, cardiovascular disease, cancer, and other medical problems. All of these conditions contribute to an overall increase in mortality (rate of death).

Are treatment plans available to help me lose weight?

There have been many treatment plans — from diets to pills — aimed at reducing weight. However, being overweight is a chronic condition and therefore needs a long-term plan aimed at weight reduction.

Your doctor or registered dietician is the ideal person to initiate and monitor an organized treatment plan for you. This treatment plan should center on behavior modification. There are also many community organizations and resources for gathering information on weight loss.

What steps should I take to help me lose weight?

  • Decide you want to permanently lose weight.
  • Educate yourself.
  • Have a realistic goal in mind.
  • Formulate a structured treatment plan with your doctor and receive proper follow-up.
  • Understand that obesity is a long-term condition and it will require life-long attention.

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