Like HowStuffWorks on Facebook!

How To Lose Weight


Body Mass Index (BMI)
Body Mass Index takes into account your height, weight, and percentage of body fat. This is significant because fat does not weigh as much as water or muscle.

Ironically, you have to accumulate larger amounts of fat than muscle (or water) in order to gain the same amount of weight. You appear slimmer when you gain weight from added muscle, but you look larger when you gain weight from added fat.

The bathroom scale is not very accurate at measuring body fat or the health risks associated with it. It can't distinguish between lean muscle tissue, organs, water weight, and body fat. Neither can it tell you where you carry most of the fat on your body.

A measurement called the body mass index, or BMI, is better than the bathroom scale at evaluating a person's health risks associated with weight. Although not a precise measurement of body fat, BMI takes body fat into account. BMI is calculated using your weight and height, so it's an easy and inexpensive way to find out if you're at a healthy weight.

To determine your BMI, use this formula:
  • Multiply your weight (in pounds) by 703.
  • Divide this number by your height (in inches).
  • Divide this number by your height (in inches), again.

To determine your BMI, visit Discovery Health's online body mass calculator.

Once you've calculated your BMI, you'll want to know what it means. BMI values are divided into categories that reflect a person's weight status: underweight, a healthy weight, overweight, or obese.

BMI Weight Category
Below 18.5
Underweight
18.5 to 24.9 Normal
24.9 to 29.9 Overweight
30.0 and above Obese

Knowing your BMI is a great starting point to maintaining a healthy weight, but it is not always the best method of measurement for some people. For example, athletes and body builders may have a high BMI, but in reality, their percent of body fat may be very low. Children should not use adult BMI tables, and the elderly may be healthier in a slightly higher BMI range to protect against osteoporosis. In addition, BMI does not tell you precisely how much body fat you have or where it's located -- two important indicators of risk.

There are other ways to tell how much body fat you have. The next page explains what those are.

For more information about losing weight, see:

  • 10 Ways to Eat Healthier: Once you know which foods are healthy for you, you can arrange them into entire meals. Get some suggestions on how to eat healthy all day long.
  • Benefits of Exercise: Regular physical activity can help you with everything from keeping weight off to preventing heart disease. Find out how to improve and extend your life through exercise.
This information is solely for informational purposes. IT IS NOT INTENDED TO PROVIDE MEDICAL ADVICE. Neither the Editors of Consumer Guide (R), Publications International, Ltd., the author nor publisher take responsibility for any possible consequences from any treatment, procedure, exercise, dietary modification, action or application of medication which results from reading or following the information contained in this information. The publication of this information does not constitute the practice of medicine, and this information does not replace the advice of your physician or other health care provider. Before undertaking any course of treatment, the reader must seek the advice of their physician or other health care provider.

More to Explore