The bathroom scale is a standard tool for anyone trying to get into better shape. Many either dread or anticipate what that little scale will say. But can the scale tell you the whole story? While it may be a good idea to keep tabs on your weight, it is also important to understand what makes up your weight.
Body composition refers to the proportion of fat you have, relative to lean tissue (muscles, bones, body water, organs, etc). This measurement is a clearer indicator of your fitness. No matter what you weigh, the higher percentage of body fat you have, the more likely you are to develop obesity-related diseases, including
high blood pressure,
type 2 diabetes.
Your body mass index (BMI) is a measurement that takes your height into account. Health professionals use BMI to calculate whether a person is underweight, normal weight, overweight, or
obese. For most people, BMI is closely associated with the amount of body fat they carry. To
calculate your BMI, divide your weight in kilograms by your height in meters squared. The guidelines are:
|Interpreting Body Mass Index|
|Obese||30.0 and above|
The problem with BMI is that it does not work for everyone. Some people’s weight and height measurements put them in the overweight or even obese category while, in reality, they are lean and muscular. On the other hand, some people’s BMI indicates that they are healthy, when they are actually overweight, with little lean tissue and too much fatty tissue. So, whether or not your BMI indicates that you are overweight, it is important to find out if you are carrying too much body fat.
There are several ways you can find out your percentage of body fat. If you have ever had your body composition tested at a gym or by a dietitian, it may have been tested with calipers. Calipers are small clamp-like devices that determine the amount of fat you have lying just below the skin by taking skinfold measurements at various locations on your body, such as the back of your arm and your waistline. Health professionals use these skinfold measurements in equations that estimate body fat.
Calipers are widely used because they are inexpensive and easy to use, but they are less accurate than other methods. Other ways of measuring body fat include:
Underwater weighing—Under water, lean tissue sinks and fat floats. Your underwater weight can be used to estimate the amount of fat mass you carry. Underwater weighing is highly accurate, but it can be expensive and time consuming, and it requires special equipment.
The Bod Pod—This machine works by measuring the amount of air your body displaces. Like underwater weighing, the Bod Pod is highly accurate, but it can be expensive and requires special equipment. The Bod Pod is, however, slightly more convenient than underwater weighing, since it does not require underwater submersion. The Bod Pod also takes less time.
Dual x-ray absorptiometry (DEXA) scan—The DEXA scan uses low-level x-rays to calculate the amount of body fat, muscle, and bone in your body. The advantages of this scan are that it is quick and it takes bone into consideration when comparing body fat to muscle.
Bioelectrical impedance—This method works by measuring the speed of an electrical current as it travels through your body. It is one of the least expensive methods of measuring body fat. It is less subject to human error than calipers, but its accuracy depends on a number of factors, including hydration, the fullness of the stomach, and how recently a person has exercised. If you are looking for a way to keep track of your body fat percentage at home, you can buy a bioelectrical impedance scale. Keep in mind though, that these scales are not always accurate and are probably better for monitoring changes in your body fat than giving you precise numbers.
So, what should your body fat percentage be? A study in the
American Journal of Clinical Nutrition
published the following information based on your sex and age:
|Body Fat Guidelines|
|Age||Healthy Body Fat % (Women)||Healthy Body Fat % (Men)|
As you can see, women naturally have a higher body fat to lean tissue ratio than men, and body fat naturally increases with age.
When it comes to losing weight, the key is to eat fewer calories than you expend. If you do this, AND exercise, you will lose body fat. Your body was designed to store fat so it would have reserves of energy during famine. When you take in fewer calories than you expend, during exercise and rest, your body burns these fat reserves. Be sensible, however—if you eat too few calories or cut out all carbohydrates, the weight you lose will likely be fluids and muscle, not fat. In this case the scale will go down, but your body fat percentage will go up, rendering you less healthy. The Academy of Nutrition and Dietetics recommends losing weight slowly—½ to 1 pound per week—and continue exercising to maximize fat loss and minimize muscle loss.
About BMI for adults. Centers for Disease Control and Prevention website. Available at: http://cdc.gov/nccdphp/dnpa/bmi/adult_BMI/about_adult_BMI.htm. Updated July 11, 2014. Accessed December 23, 2014.
BMI calculator. Calorie Control Council website. Available at: http://www.caloriecontrol.org/healthy-weight-tool-kit/body-mass-index-calculator. Accessed December 23, 2014.
Body composition. Georgia State University website. Available at:
http://www.gsu.edu/~wwwfit/bodycomp.html. Accessed on December 23, 2014.
Diets for weight loss. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated December 8, 2014. Accessed December 23, 2014.
Gallagher D, Heymsfield SB, Heo M, et al. Healthy percentage body fat ranges: guidelines based on body fat index.
Am J Clin Nutr. 2000;72:694-701.
It's about eating right. Academy of Nutrition and Dietetics website. Available at: http://www.eatright.org/Public/content.aspx?id=6851. Updated November 2012. Accessed December 23, 2014.
Last reviewed December 2014 by Michael Woods, MD
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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