Body Mass Index: A 2-Minute Primer

What is your Body Mass Index how is it used?

The Body Mass Index (BMI) is one of several ways to measure the amount of excess fat (adipose tissue) in the body. Healthcare providers use BMI to determine your overall fitness and your risk of developing chronic diseases. You can also monitor your own BMI to track the results of your own diet and exercise plan if you’re trying to manage your weight.

BMI has its critics, and it’s true that there are other techniques, including hydrodensitometry (underwater weighing), skinfold measurements (using calipers) and magnetic resonance imaging (MRI) that can provide more accurate determinations of body fat. However, BMI can be still be quite useful in most cases since it allows an effective comparison across large populations and is statistically well-correlated to adiposity. Plus, it’s easier for most people to monitor on an ongoing basis.

How do you calculate your BMI?

Your BMI is essentially the ratio of your weight to your height squared. More specifically, BMI is calculated using the following formula:

BMI = weight / (height)2

Note that the formula above uses the metric system, with weight in kilograms and height in meters. To calculate your BMI based on height in inches and weight in pounds, just multiply the result by 703.

BMI = weight (lbs.) / (height [in.])2 x 703.

What does your BMI mean?

Here are the standard weight categories associated with BMI ranges for adults who are 20 years of age and older:

BMI  Below 18.5         Underweight

BMI 18.5 to 24.9         Normal or Healthy Weight

BMI 25.0 to 29.9         Overweight

BMI 30.0 and Above   Obese

Does having a high BMI always mean carrying extra fat, and vice-versa?

No, it doesn’t. As we mentioned earlier, BMI is generally a useful way to measure body fat. However, there are a few scenarios in which BMI doesn’t accurately capture the true situation. For examples:

  • Athletes and others with a high lean body mass (muscle and bone) may fall into the overweight category despite having very little body fat.
  • Elderly people and those who have lost muscle mass may fall into the underweight category despite having excess body fat.
  • At the same BMI, women tend to have more body fat than men do.
  • At the same BMI, Whites tend to have less body fat than Asians but more than African-Americans.

Experts believe that body composition and weight distribution can also affect your health. However, BMI doesn’t provide any information about these factors. The fact that BMI isn’t perfect is a good reason to look at other measures as well—such as your waist circumference—to get a clearer picture. It’s also a good reason to have your overall health evaluated by a trained healthcare provider who can interpret your BMI and other measurements correctly and put them in proper context.

Health Risks Associated with High BMI

High BMI is associated with a variety of other risk factors related to chronic health problems such as Type 2 diabetes, heart disease, high blood pressure, gallbladder disease and some types of cancer. These other risk factors include:

  • High LDL cholesterol (“bad” cholesterol)
  • Low HDL cholesterol (“good” cholesterol)
  • High blood sugar
  • High triglycerides
  • Sedentary lifestyle
  • Smoking

How much BMI do I need to loss to see improvements?

It may seem like you need to increase exercise and/or cut calories a LOT to lose a meaningful amount of weight. However, even a 5% or 10% reduction in body weight can help lower the risk of obesity-related diseases. Be sure to check with your doctor before beginning a new weight management program. This is especially important if you have a known medical condition or if you haven’t been physically active for a while.

If you or someone you care about is interested in weight loss or weight management as a way to improve overall health and wellness, we can help! Just call or visit our office today!

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