Article # 61. Body Mass Index (BMI)

Body Mass Index

Body Mass Index (BMI) is a number calculated from a person's weight and height. BMI provides a reliable indicator of body fatness for most people and is used to screen for weight categories that may lead to health problems.

Your body is made up of water, fat, protein, carbohydrate and various vitamins and minerals. If you have too much fat — especially if a lot of it is at your waist — you're at higher risk for such health problems as high blood pressure, high blood cholesterol and diabetes. That increases your risk for heart disease and stroke.

Obesity is now recognized as a major, independent risk factor for heart disease. If you're overweight or obese, you can reduce your risk for heart disease by successfully losing weight and keeping it off.

Waist circumference and body mass index (BMI) are indirect ways to assess your body composition. Waist-to-hip ratio (WHR) is another index of body fat distribution. However, WHR is less accurate than BMI or waist circumference and is no longer recommended.

Questions about BMI

What is the waist circumference?

Waist circumference is the distance around your natural waist (just above the navel). If your BMI is greater than or equal to 25 kg/m², your goal for waist circumference is less than 40 inches if you're a man and less than 35 inches if you're a woman.

What is the body mass index (BMI)?

Body mass index assesses your body weight relative to height. It's a useful, indirect measure of body composition because it correlates highly with body fat in most people. Weight in kilograms is divided by height in meters squared (kg/m²).

·    BMI values less than 18.5 are considered underweight.

·    BMI values from 18.5 to 24.9 are healthy.

·    Overweight is defined as a body mass index of 25.0 to less than 30.0. A BMI of about 25 kg/m² corresponds to about 10 percent over ideal body weight. People with BMIs in this range have an increased risk of heart and blood vessel disease.

·    Obesity is defined as a BMI of 30.0 or greater (based on NIH guidelines) — about 30 pounds or more overweight. People with BMIs of 30 or more are at higher risk of cardiovascular disease.

·    Extreme obesity is defined as a BMI of 40 or greater.

Some well-trained people with dense muscle mass may have a high BMI score but very little body fat. For them, the waist circumference, the skinfold thickness or more direct methods of measuring body fat may be more useful measures. 

Why is BMI screening important to children and families?

BMI is a screening tool that helps identify children who may be at risk for weight problems. A BMI that places a child below the 5th percentile may mean that the child is not growing well. It also may mean that the child is at risk of having an eating disorder. Children with BMIs that place them above the 85th percentile are considered overweight. Those with BMIs that place them above the 95th percentile are considered obese. Children with abody mass index that places them in the 85th percentile or above are at risk for adult diseases such as type 2 diabetes, high cholesterol and high blood pressure. If your child’s BMI is not in the healthy range, you should have your child examined by a physician who can conduct a complete evaluation.

Concern:

Why be concerned about your BMI and/or waist circumference or that of your child or yourself?

Unfortunately there are a number of diseases that could be prevented by watching these two measurements. They include: high blood pressure, high blood cholesterol or other lipid disorders, type 2 diabetes, heart disease, stroke, and certain cancers. The nice thing is that a weight loss of only 10% of your current weight will help reduce your risk of developing those diseases.

Tips:

Controlling weight is not easy, but by serving a nutritious diet including the basics of fruits, vegetables, whole grains and low fat dairy and low fat meat products will help. Increasing physical activity to about an hour a day will help. Making these priorities as a family will go a long way to keeping everyone in the family fit and healthy for many years of excellent health.

BMI Calculation:

To calculate your BMI without a chart you can use this formula: (Weight in pounds)/[(Height in inches)X(Height in inches)] x 703.