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What Does Body Composition Mean?

What Is Body Composition and How Is It Measured?

Definition of Body Composition

In physical fitness, body composition is defined as the percentage of fat, muscle, and bone in the body. Usually its expressed as a ratio of lean mass to fatty mass. Lean mass includes muscle, bone, skin, internal organs and body water. Fatty mass is mostly composed of body fat (subcutaneous fat) as well as internal essential fat surrounding organs. Body composition will typically be displayed as either a percentage of fat (body fat percentage or %fat) or as a percentage of lean body mass (LBM).

Why Is Body Composition Important?

Body composition is a much more accurate representation of a persons leanness than scale weight or Body Mass Index (BMI), because it does not rely on height and weight alone to measure leanness.  It measures the ratio of body fat to lean tissue and bone in the body, not scale weight.

This is important, because a person may have a high-scale weight (even for their height), yet have also have a high muscle-to-fat ratio which makes them extremely lean. That same person might be labeled overweight using the standard BMI calculation, which does not take into account body composition, only mass (weight) relative to your height, weight, age and gender.

Excess body fat, or a body composition with a high fat-to-muscle ratio is unfavorable because it increases the risk of cardiovascular disease, Type II diabetes, Metabolic Syndrome and certain cancers. Excess body fat, especially at levels considered obese, can also put stress on the joints and interfere with mobility and the ability to perform everyday activities.


Body Composition and Physical Performance

For athletes or even weekend warriors who participate in competitive or recreational sports excess body fat can impair physical performance. In general, the less body fat, the better the performance. Body fat contributes no strength advantage to a person (unlike muscle), and can interfere with endurance, speed and agility.

From a purely aesthetics perspective, two people can have the exact same height and weight, yet look completely different due to variations in their body composition. Since fat takes up more space on the body, a person who has a high body fat percentage but the same height and weight as a person with a low body fat percentage and more lean muscle will look larger and less lean. This is why its important to use body composition, and not scale weight, to determine overall physical fitness and leanness.

Measuring Body Composition

There are a number of techniques and devices for testing and measuring body composition, including:

  • Body fat calipers (hand-held, manual or electronic) which measures subcutaneous fat using a single or multiple skin fold tests
  • Bioelectrical Impedance Analysis (BIA), which measures body composition by passing a weak electrical current through the body. The most common BIA devices are electronic body fat scales, although there are also hand-held versions.
  • Hydrostatic Weighing,which involves submerging the body in a tank of water and measuring the buoyancy of the body (more muscle mass causes the body to sink, while more body fat causes it to rise.)
  • Air Displacement Plethysmography (ADP) which uses the same principle as hydrostatic weighing, but instead measures the displacement of air in a sealed chamber, verses water.
  • Dual X-ray Absorptiometry (DXA) uses a low-level X-ray to give very precise measurements of bone mineral content (BMC), bone mineral density (BMD), lean tissue mass, fat tissue mass, and % of fat.
  • Magnetic Resonance Imaging or Computed Tomography, which like DXA, provides very detailed and accurate body composition measures.

The most common, inexpensive and accessible forms of body composition testing for most people continue to be calipers and bioelectrical impedance analysis.

Of the two, calipers are considered to be the most accurate typically within four percentage points of a persons actual body fat percentage which is usually sufficient for most people. The difference in accuracy between single-point skin fold caliper tests and multiple-point tests is marginal, and research has shown that a single-point test, when properly done, can be almost as accurate as hydrostatic weighing.

Calculating Body Composition

Body composition is calculated by taking a persons body fat percentage, and subtracting it from a persons total scale weight.

For instance, a 200 lb man with 10% body fat would have 180 lbs of lean mass, and 20 lbs of body fat, or 90% lean mass. Unlike BMI, height, age and gender are not a factor in calculating body composition, although age and gender do come into play when determining ideal body composition targets.

Recommended Body Composition

The National Institutes of Health (NIH) recommends that healthy adult men should have between 13-17 percent body fat, while adult women should have between 20-21 percent body fat. Men who have a body fat percentage that exceeds 25% and women who have more than 30% body fat are considered obese.

However, athletes or people participating in competitive sporting activities may benefit from even lower body fat levels than recommended by the NIH.

Theideal body composition may also vary depending on the type of sport or activity.

For example, the typical body fat percentage for a male basketball player is 9% (13% for women), while the average Olympic cross-country skier has 5% (11% for women) body fat. This has to do with the type of activity and motion involved in cross-country skiing, where less body fat-to-greater lean tissue is advantageous to the competitor because it maximizes power, while reducing drag.

Most female fitness models will have body fat percentages in the mid-to-low teens, while competitive female bodybuilders or figure competitors will have body fat levels in the high single-digits. Male bodybuilders when preparing for a show will often have body fat levels in the low single digits. However, in both female and male bodybuilding, these low body fat percentages are typically not sustained year-round, and are usually only attained in the weeks leading up to a competition.

Can You Have Too Little Body Fat?

While having a body composition that favors more muscle and less fat is generally a good thing, it is possible to have too little body fat. The body needs a certain amount of essential body fat to cushion organs, regulate temperature, and regulate certain essential body nutrients as well as produce hormones.

For men the amount of essential body fat is around 3 percent, for women its considerably higher, about 12 percent. While it is possible for people to drop below those minimum levels for short periods of time, consistently maintaining body fat percentages below these essential body fat levels can have serious long-term health effects. For example, in women, maintaining very low body fat levels (sub 13%) can intefere with normal menstruation and cause hair-loss, skin disorders and organ damage in both genders.


Comments (5)

  1. Barb Smith (1 comments) says:

    If  you are in a friendly competition like the TV show, The Biggest Loser, should we use % of body fat lost and not the BMI for a person?   I am finding that my BMI continues to go up each week as well as my weight.  I consider myself an athlete as I work out 7 days a week, weight training, running, core workouts.  I am seeing results in my slothing fitting more loosely but the numbers arent showing it.  The weight doesnt bother me.  I know that I have gained muscle which would make my BMI increase, right?

    • Matt (194 comments) says:


      I would recommend using percentage of body fat lost, versus scale weight or BMI for your Biggest Loser competition. Using percentage body fat will help equalize any advantages that one person may have over the other at the start. So if one of you has less body fat than the other, you can still compete on a level playing field. BMI will not be precise enough for you needs in terms of measuring progress on changing your body composition.

      Heres how I would do it: Get a pair of body fat calipers. The Accumeasure 3000 Body Fat Calipers are all youll need. You can sometimes buy them at the gym or at a fitness or sporting goods store, or here on for under $10.

      Take an initial measurement, and use the chart that comes with the calipers to calculate your body fat percentage. You can then combine this with a scale weight to figure out your actual ratio of lean mass to body fat.

      Next, set either a percentage lost goal or a specific timeline as your target. The first person to reach that goal wins. For example, maybe you goal is to see who can lose 10% of their body fat first, or who can lose the most body fat in six weeks.

      If you only used total pounds lost, one person might have a starting advantage since they might weigh more, and thus be prone to losing more weight initially. Also, using body fat percentage keeps you focused on making positive changes to your actual body composition, versus just looking at scale weight lost, which can include lean muscle loss, not just fat.

      Great challenge by the way. Keep us posted on your progress and who wins. Best of luck!

  2. Edward Gonzalez (1 comments) says:

    I have a LBM of 128.21 and I weight 155.21 lbs.  Is this good?  I am trying to lose weight for my height to be at 150.  Each week my LBM goes down.  Should that number be higher each time?  Am I exercising too much?

  3. Kelly (4 comments) says:

    Thanks for the information.  I am a competitive (well used to be) runner and at the time my body fat was at about 3-4% when I was an 18year old male.  Now, that number has increased and my overall weight has increased too.  A friend of mine always had a much higher body fat %, but was usually in good running shape.  He attributed it to the fact that he was a swimmer and that swimmers were known to have more body fat? Is there any scientific truth to this and if so, why?