Body Mass Index
Body mass index (BMI) is calculated using height and weight. It is used to estimate body fat.
Starting at 25.0, the higher your BMI, the greater is your risk of developing obesity-related health problems. These ranges of BMI are used to describe levels of risk:
- Overweight (not obese), if BMI is 25.0 to 29.9
- Class 1 (low-risk) obesity, if BMI is 30.0 to 34.9
- Class 2 (moderate-risk) obesity, if BMI is 35.0 to 39.9
- Class 3 (high-risk) obesity, if BMI is equal to or greater than 40.0
Obesity is a medical condition in which a high amount of body fat increases the chance of developing medical problems.
People with obesity have a higher chance of developing these health problems:
- High blood glucose (sugar) or diabetes.
- High blood pressure (hypertension).
- High blood cholesterol and triglycerides (dyslipidemia, or high blood fats).
- Heart attacks due to coronary heart disease, heart failure, and stroke.
- Bone and joint problems, more weight puts pressure on the bones and joints. This can lead to osteoarthritis, a disease that causes joint pain and stiffness.
- Stopping breathing during sleep (sleep apnea). This can cause daytime fatigue or sleepiness, poor attention, and problems at work.
- Gallstones and liver problems.
- Some cancers.
Three things can be used to determine if a person's body fat gives them a higher chance of developing obesity-related diseases:
- Body mass index (BMI)
- Waist size
- Other risk factors the person has (a risk factor is anything that increases your chance of getting a disease)
Having a risk factor doesn't mean that you will get the disease. But it does increase the chance that you will. Some risk factors, like age, race, or family history can't be changed.
The more risk factors you have, the more likely it is that you will develop the disease or health problem.
Your risk of developing health problems such as heart disease, stroke, and kidney problems increases if you're obese and have these risk factors:
- High blood pressure (hypertension)
- High blood cholesterol or triglycerides
- High blood glucose (sugar), a sign of type 2 diabetes
These other risk factors for heart disease and stroke are not caused by obesity:
- Having a family member under the age of 50 with heart disease
- Being physically inactive or having a sedentary lifestyle
- Smoking or using tobacco products of any kind
Summing it up
You can control many of these risk factors by changing your lifestyle. If you have obesity, your health care provider can help you begin a weight-loss program. A starting goal of losing 5% to 10% of your current weight will reduce your risk of developing obesity-related diseases.
Women with a waist size greater than 35 inches (89 centimeters) and men with a waist size greater than 40 inches (102 centimeters) have an increased risk for heart disease and type 2 diabetes. People with "apple-shaped" bodies (waist is bigger than the hips) also have an increased risk for these conditions.
Cowley MA, Brown WA, Considine RV. Obesity: the problem and its management. In: Jameson JL, De Groot LJ, de Kretser DM, et al, eds. Endocrinology: Adult and Pediatric. 7th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 26.
Jensen MD. Obesity. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 220.
Moyer VA; U.S. Preventive Services Task Force. Screening for and management of obesity in adults: U.S. Preventive Services Task Force recommendation statement. Ann Intern Med. 2012;157(5):373-378. PMID: 22733087