Home Am I at Risk? Obesity, Overweight, and Heart Disease

Obesity, Overweight, and Heart Disease

What is obesity and overweight?

Obesity and overweight don’t mean exactly the same thing—obesity is a more severe form of being overweight. Because your ideal weight is related to how tall you are, doctors use a scale called the body mass index (BMI) to determine what a healthy weight for you might be. Your BMI is calculated by taking your weight in kilograms and dividing it by your height in meters squared. You can calculate your own BMI here (it will do the conversion to kilograms and meters for you).

A BMI between 25 and 29.9 is considered overweight, while obesity is defined as having a BMI of 30 or more. A woman with a BMI of 30 is about 30 pounds overweight. Obesity is then further broken down into 3 categories: Class I, Class II, and Class III. The table below shows the BMI cutoff points for underweight, normal weight, overweight, and the 3 classes of obesity.

BMI Categories of
Overweight & Obesity1

BMI Category
Less than 18.5 Underweight
18.5 to 24.9 Normal weight
25 to 29.9 Overweight
30 to 34.9 Class I Obesity
35 to 39.9 Class II Obesity
More than 40 Extreme Obesity

The main causes of being overweight or obese are eating too much and not being active enough. If you eat more calories than your body burns up, the extra calories are stored as fat. Other factors that may affect your weight include your genes (obesity tends to run in families),2, 3 your metabolism (how your body processes food),4 and your age (your metabolism slows down as you get older). Sometimes an illness or medication can contribute to weight gain.

How common is overweight and obesity?

The National Center for Health Statistics estimates that 64% of all Americans over 20 years old are overweight or obese.5 Since 1993, obesity in the US increased 61%.6 More than 62% of all American women are overweight or obese.7 Obesity tends to vary between racial and ethnic groups, and is particularly common in black and hispanic women. It is also a growing problem among children.8

How accurate is BMI?

For some people, BMI might not accurately gauge their health risk. For example, because muscle weighs more than fat, a very muscular person may have a BMI over 25, even though they are not really overweight or at increased risk for heart disease. For South Asians, Arabs, and mixed-race Africans, BMI can also be inaccurate because people with this ancestry tend to have a higher percentage of body fat than white people. 14-17 For Asian Americans, BMI may underestimate their health risk.18, 19 BMI may overestimate the risk of heart disease in older people.14

Increasingly, studies show that waist measurement (for Chinese people and black Africans) and/or waist-to-hip ratio are better than BMI for assessing the risk your weight poses to your heart health.1

What about weight gain during pregnancy?

When a woman is pregnant, it is normal for her to gain weight. The recommended weight gain during pregnancy depends upon your weight before you became pregnant. Women who are of normal weight should gain 25 to 35 pounds during pregnancy. Overweight women should only gain 15 to 25 pounds, and obese women should gain no more than 15 pounds.20 You should not try to lose weight if you are pregnant.

Next: Excess Fat & Your Heart


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