Healthy Weights and BMI
The USDA Dietary Guidelines urge all Americans to achieve and maintain a body weight that
optimizes their health. But how do you know how much you should weigh?
Just as there is no magic weight-loss bullet, there's no magic number on the scale, either. But you can determine whether your weight and the amount of body fat you are carrying are within a range of weight that is optimal for your health. Once you've done that, you can go ahead and set a more specific goal weight.
There are two primary methods of measuring body fat, the Body Mass Index (BMI) and waist circumference. The USDA Dietary Guidelines recommend that you use both measures to assess your current weight and to monitor your weight whether you're in the weight-loss or maintenance phases of your weight-control plan.
Body Mass Index (BMI)
The Body Mass Index (BMI) is a measure of a person's weight
in relation to height. But don't confuse it with the traditional height and weight tables that used to be on display in your physician's office.
BMI is calculated with a formula, and it produces a number that indicates whether your weight falls into a range that's optimal for health. BMI is considered a more accurate measurement of body fat than weight alone in people 20 years of age or older. (For assessment of young people ages 2 to 19 years, visit www.cdc.gov/growthcharts.)
To calculate your BMI, weigh yourself first thing in the morning, wearing few or no clothes. Confirm your height and convert it to inches. Multiply your weight in pounds by 700 (using a calculator makes these computations quicker and easier). Divide this result by your height in inches. Then divide this result again by your height in inches. This number is your BMI. (You can also insert your height and weight into a BMI calculator at a Web site run by the Centers for Disease Control at www.cdc.gov/nccdphp/dnpa/bmi/calc-bmi.htm.)
Here's an example of BMI calculations for a 140-pound person who is 5 feet 6 inches tall:
140 (weight in pounds) X 700 = 98,000 divided by 66 (height in inches) = 1,484.85 divided by 66 (height in inches) = 22.49.
A BMI between 19 and 24.9 is considered to be in the healthy range and is associated with the least risk of heart disease or other health problems related to being overweight. So the person in the example above is right in the middle of the healthy range. Health risks begin when BMI is 25.0 to 29.9. They become even greater when BMI is higher than 30.0.
If you have a BMI that puts you in the "obese" category, don't despair. There are health benefits to even a modest weight loss of ten pounds. And you can significantly reduce your health risks by losing just ten percent of your weight. The lifestyle changes you're about to make will automatically lower your health risks -- you're on the right path!
Even if your BMI places you in the healthy weight range, it's important to take steps to prevent weight gain, which happens as you age because of metabolic changes even if you continue to eat the same number of calories. Preventing weight gain by eating fewer calories as you get older is also critical to your health.
Although it's a good indicator of body fat and health risk, BMI measurement is not perfect. It can overestimate the amount of body fat in people who are very muscular, because muscle is more dense than fat. And it can underestimate the amount of body fat in people who have lost muscle mass, such as the elderly. Even so, BMI is the preferred method of assessing health risks related to weight and amount of body fat.
Where's Your Fat At? -- Waist Circumference
In addition to BMI, it is important to consider where you
carry your extra weight. If fat tends to gather in your abdominal area, you may have increased health risks.
Large stores of fat around the waist are associated with a risk of heart disease, diabetes, and some cancers for those who have a BMI of 35 or less. (Waist circumference does not indicate any additional risks for those with a BMI greater than 35.)
" >To measure waist circumference, place a tape measure around the top of the hip bone. This location may not be what you consider to be your natural waistline, since it is not the narrowest part of your midsection. However, it is the position where you will get the most accurate measure of your abdominal circumference and therefore the best indication of where fat is being stored.
Pull the tape snuggly but not so tight that it indents the skin. Take the measurement after a normal exhalation of breath. Read the tape measure in inches. A waist circumference of 40 inches or more for men or 35 inches or more for women indicates that you are at greater risk of health problems, even if your BMI alone doesn't indicate that. Your waist circumference can put you in a high-risk category when your BMI does not.
Now you know what your target weight should be, at least in general terms. In the next section, we will talk about setting a realistic weight-loss goal and answering the question -- what does it take to get there?
Does your BMI put you at risk?
Body Mass Index
Less than 19.0 = Underweight
19.0-24.9 = Healthy weight
25.0-29.9 = Overweight (Moderate risk for health problems)
30.0 and greater - Obese (High risk for health problems