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What is Body Composition?

Find Out Why Body Composition Matters if You Are Trying to Lose Weight

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Updated December 05, 2012

What is Body Composition?
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In fitness and weight loss circles, people often talk about body composition. But what is body composition and why does it matter? If you’re trying to lose weight and especially if you are a woman over the age of 40, the answers may hold the key to long-term weight loss and weight maintenance.

What is Body Composition?

Your body is made up of fat mass and fat-free mass. Fat-free mass includes lean muscle, bones, organs, tissue and water. When people refer to body composition, they are generally talking about body fat percent, or the percentage of your body mass that is fat.

You can't change the part of your body that is bones, tissues and organs, but you can change the ratio of fat to muscle with good training and proper diet. Lean muscle mass burns more calories than fat, shapes your figure, and helps your body to function more efficiently throughout your daily activities. So increasing your muscle mass is in your best interests if you want to lose weight, look better in your clothes, and feel better during the day.

How is Body Composition Measured?

There are several different methods used to determine how much fat your body is carrying. For many years, the gold standard has been hydrostatic weighing. During this process your body is submerged in a huge tank to see how much water is displaced. A new method called DeXA scanning is now recognized as a highly accurate method as well. But both of these methods are very expensive and not widely available.

Other more accessible methods include:

  • Bioelectrical impedance. BIA devices send an electrical current through the body to measure lean body mass and determine body fat. The most common BIA devices are body fat scales.
  • Skinfold calipers. Many health clubs and personal trainers use skin calipers to measure folds of fat on your body. A skilled practitioner will use measurements from three different sites to determine an estimated overall body fat percent. The accuracy of this method depends entirely on the skill level of the person doing the measuring.
  • BodPod. This egg-shaped device is a relative newcomer to the fitness and health market, so it is not as widely available in all areas. BodPod uses the same principle as hydrostatic weighing but measures air displacement instead of water displacement.

Does BMI Measure Body Composition?

BMI, or body mass index is an assessment of body weight, but it is not a measure of body fat. BMI is often used in clinical settings such as a doctor’s office to determine if your weight is healthy. BMI is determined using your height and weight.

Why Does Body Composition Matter for Weight Loss?

A body with more muscle and less fat is a more efficient calorie-burning machine. But you don't have to be a body builder to reap the benefits.

  • A lean, strong body is a more efficient exerciser. As you become more fit, you are more capable of completing high intensity workouts that burn more calories and create greater improvements in the look and feel of your body.
  • Muscles burn more calories than fat. A lean, strong version of your body will burn more calories and have a better metabolism than the version of your body with more fat.
  • Studies have shown that particularly in peri-and post menopausal women those who maintain a very physically active lifestyle tend to gain less weight than those who don’t.
  • For aging women in particular, gaining more muscle and maintaining a good body composition is a great way to keep a lean physique and fit shape.

How Do I Change My Body Composition?

The good thing about body composition is that it is possible to change it to improve the way that you look and feel. To change your body composition, you need to eat a healthy diet that is low in fat and contains enough protein to build and maintain muscle.

A well-balanced exercise plan is essential as well. A good training program needs to include plenty of strength training to build muscle as well as high intensity aerobic activity, and moderate endurance cardio for burning fat. It's also a good idea to do flexibility work to keep your muscles and joints healthy.


For many people, getting on the scale is difficult. But if you focus on body composition, the struggle can be a little bit more tolerable. Weight can fluctuate from day to day, but if you set a goal based on creating muscle and building a lean frame, you’ll ensure better results in the long run.

American College of Sports Medicine. " ACSM Issues Position Stand on Exercise and Older Adults." 2009.

William J. Evans, PhD " Protein Nutrition, Exercise and Aging." Journal of the American College of Nutrition 2004.

Sternfeld, Barbara, Bhat, Aradhana K. Wang, Hua, Sharp, Teresa, Quesenberry, Charles. "Menopause, Physical Activity, and Body Composition/Fat Distribution in Midlife Women." Medicine & Science in Sports & ExerciseJuly 2005.

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