Why use body composition instead of weight

Weight alone isn’t necessarily a good health and fitness indicator

Many people use the scale and BMI (body mass index) as an indicator for determining their healthy, fitness weight.But the drawback of using a scale and BMI chart alone is that neither assess your body composition and cannot tell how much of your total weight is comprised of water, fat, or muscle.For those not familiar with BMI, it uses your height and weight to determine if you fall into one of the following categories:

  • Underweight: Your BMI is less than 18.5
  • Healthy weight: Your BMI is 18.5 to 24.9
  • Overweight: Your BMI is 25 to 29.9
  • Obese: Your BMI is 30 or higher

This BMI method is unreliable for those with a lot of lean muscle. At 5’9”, 185 pounds, and 10% body-fat, the BMI chart suggest I’m overweight with a BMI of 27.3

What is Body Composition?

Body composition is the proportion of fat and lean tissue in your body and a better indication of your health and fitness. Healthy body composition is one that has a lower percentage of body fat and a higher percentage of lean tissue, which includes muscle, bones, and organs. Body fat percent is a measurement of body composition identifying how much of the weight of your body is fat and how much is lean tissue. The health and fitness ranges for body fat differ for men and women.

Healthy Body Composition

How to Measure Your Body Composition

There are several methods to get an estimate of your body fat percentage at home, at the gym, or from your healthcare provider:

Bioelectrical Impedance

Bioelectrical impedance is the method used by handheld units and by BIA body fat scales which sends a small electrical current through your body. Fat, water and lean tissue affect the current difference to give the reading of fat percentage, but I haven’t found one of these units that accurately measured my body-fat percentage yet. Many factors may affect accuracy such as:

  • Hydration
  • Fitness level
  • Recent physical activities
  • Recent food and beverage consumption


A DEXA scan or dual-energy x-ray absorptiometry scan is performed in a medical setting and it’s used to measure fat, muscle and bone composition.

Hydrostatic Weighing

Hydrostatic weighing is a method that requires you to be fully submerged in water. This method is suggested to be one of the most accurate, but locations with these tanks are few, and it could be costly if you plan on tracking progress.

Skinfold Measurements

Taking skinfold measurements is a method often used by fitness trainers or as part of a weight loss program. Calipers are used to take measurements at different parts of your body and input into a body-fat calculator. Skinfold measurement is the method I used when preparing for bodybuilding shows. I also used it for monitoring my clients’ body compositions. Although studies have suggested a plus-or-minus of 3.5% accuracy, it worked well for my show preparations and was useful for tracking improvements with my clients. This method of body fat measurement is the least expensive and easy to perform. All you need is a caliper, a scale, and access to a skin fold calculator or body-fat calculator, which can be found online easily. There are many manufacturers of calipers, but I found that the Slim Guide Skinfold Caliper to be most comfortable to use. It has a trigger operation with a pistol-grip handle. The jaw pressure is automatically adjusted to provide consistent, reliable pressure.

Bottom Line: To know where your body composition falls in the health and fitness range, you need to measure your body fat percentage.