Body Composition and Why It Matters to You

The number on the bathroom scale flashes- whew! It’s within the recommended range. So you’re healthy. Good to go! No reason to exercise for you, right?


While the number on the bathroom scale serves as one of the most accessible and reliable indicators of health, there’s one other assessment you might want to consider before your write yourself off as a health virtuoso.

Although the scale tells you how much you weigh, body composition tells you how much of that weight is from lean (muscle) tissue and how much is from fat tissue.

If your body composition scores fall within the expected healthy ranges, your body is able to perform at its optimal level. Many of the physiological processes taking place within your body are carefully regulated by body fat, and too little or too much can throw off this intricate balance.

Although we usually equate the word fat with the stubborn roll atop our waistband or the dimpling across the back of a thigh, some fat is necessary for basic physiological functions within the body. This type of fat is referred to as essential fat.

Women have an essential fat value of 12%; men, a much lower 3%.

Body fat existing beyond essential fat ranges is referred to as nonessential fat.

Women with a total body fat percentage (essential +nonessential fat) between 12 -32 % and men with a total body fat percentage between 10 – 22% are considered to be in good condition so far as body fatness is concerned.

Although extra body weight beyond the accepted healthy ranges can generally be attributed to excess fat, and is therefore indicative of a higher body fat percentage, those falling within their accepted healthy weight ranges may still have a high percentage of body fat due to inactivity or condition such as sarcopenia.

Therefore, regardless of weight, exercise is imperative in maintaining healthy body composition.

How Do I Know If I Need To Change My Body Composition?

A wide variety of methods exist to assess body composition. Bod Pods, hydrostatic weighing, and biochemical measurements are among the most accurate means of evaluation, but these tests are often costly and/or inaccessible to the general public.

Callipers generally provide the most cost-effective and reliable means of assessing body composition. When collected by a trained professional, skinfold measurements accurately portray levels of body fatness.

Although hand-held sensors or scale sensors are often available at gyms or on bathroom scales, these tools can be widely inaccurate and are highly influenced by hydration status.

Given that the processes used to determine body composition can be difficult and time-consuming, it should be a relief to know that for the general population, body weight and BMI can still provide a fairly reliable indication of body composition status, especially if your BMI is higher than 25.

Generally, any excess weight pushing your BMI over 25 can be attributed to fat.

Often, people believe that they have “always been predisposed to a higher weight”, and that therefore, a higher weight must be healthy for their body. “I’ve always been bigger!” they may proclaim. While this may be true, a higher weight is usually due to poor eating and exercise habits that have taken place over a lifetime rather than any natural predisposition to being overweight.

For trained athletes or incredibly lean individuals, a higher BMI may indeed be caused by a high percentage of lean (muscle) mass. However, these individuals are outliers from the general population, for whom BMI is quite accurate.

How Can I Change My Body Composition?

Body composition can be altered by losing fat mass, gaining lean (muscle) mass, or both. For most individuals, losing weight is the quickest way to influence body composition, because any excess weight generating a BMI over 25 is usually due to an excess of nonessential fat.

Whether you’re pursuing weight loss or are already at a healthy weight and are interested in altering your body composition, exercise is the best means by which to achieve your goals.

Exercise works to improve body composition by adding lean mass and subtracting fat mass.

The best exercises for improving body composition are those performed at a high intensity, although any exercise has the potential to positively affect body composition.

In a study published in the journal Medicine & Science in Sports & Exercise, women who completed high intensity exercise (working at 70-85% of their MHR) burned significantly more fat than their peers working at a lower exercise intensity (50-60% MHR) during a 16 week period.

It is important to note that exercise intensity is very subjective. For instance, your body’s interpretation of intense exercise is likely very different from that of a trained athlete. Maximum heart rate (MHR) is used to measure work intensity- a higher heart rate is indicative of a high intensity workout for that individual.

MHR (maximum heart rate) can be calculated by subtracting your age from 220. Low intensity exercises are performed at 50-60% of MHR and higher intensity exercises are those working at higher than 70% of MHR.

Heart rate can be measured via a portable device or the handheld sensors on an exercise machine,

although the latter can often be inaccurate, especially after prolonged/heavy use.

To accurately gauge heart rate, invest in a monitor, or take your pulse at the juncture of your wrist- count the number of beats in fifteen seconds and multiply by four to find your number of beats per minute.

The talk test also serves as a reliable and accessible window to gauging exercise intensity. In high intensity exercise, talking should be difficult or nearly impossible. During low intensity exercise, you should be able to maintain a slightly breathless conversation.


  • (American College of Sports Medicine )ACSM | ACSM in the News.” ACSM | ACSM in the News. N.p., n.d. Web. 15 Jan. 2013.
  • ACSM | Articles.” ACSM | Articles. N.p., n.d. Web. 12 Jan. 2013.
  • ACSM | Articles.” ACSM | Articles. N.p., n.d. Web. 15 Jan. 2013.

Last Reviewed 11/Mar/2014


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Whilst wielding a couple of dumbbells in a gym class in 2003, Kate experienced an epiphany around the lack of accepted best practice guidelines when it came to staying well and avoiding disease. Kate realized that she had no chance of slowing her own aging process unless she became better educated about her options.

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