Body Composition: What It Is and What You Need to Know

Two women in fitness clothing


The number on the scale is a poor indicator of what's really going on with your body. For instance, the scale can't tell you if you're building muscle, losing fat, or both. Your body composition is unique and based on how much fat and lean mass you have. A healthier body composition is one that's higher in lean mass compared to body fat.

Meet the Expert

  • Chad Walding is a doctor of physical therapy and co-founder of NativePath.
  • Danyele Wilson is a trainer for Tone & Sculpt.

Knowing your body composition can provide you with a clearer picture of what's really going on with your body if you're working out and hoping to gain muscle or lose fat. It's also a better way to tell if your weight is appropriate and healthy for you.

What Is Body Composition?

Body composition refers to the proportion of fat and non-fat mass you have in your body relative to lean tissue such as muscles, bones, body water, and organs.

 How Is Body Composition Measured?

Body composition is a more tricky and precise measurement than body weight. However, there are a few ways to measure body composition, described here by physical therapist Chad Walding and trainer Danyele Wilson.

  • Bioelectrical impedance: A small electrical current passes through your body and can be measured by handheld units and by BIA body fat scales that you step onto like a regular scale. Many scales are sold for home use, and no special training is required. Some scales, like the Fitbit Aria 2, even sync with your fitness tracker so that you can see how changes to your daily activity and diet affect your weight. 
  • Skinfold measurements: This is a method often used by fitness trainers or as part of a weight loss program. Calipers take measurements at different parts of your body, like your thighs, abdomen, lower back, and arms, and then a calculation helps translate them into a body fat percentage.
  • DEXA scan: Dual-energy x-ray absorptiometry. This body scan is done in a medical setting and is often looked at as the most accurate body composition reading.
  • Hydrostatic weighing: Your body is weighed on land and then underwater, and the difference helps determine your body’s density. The heavier you are underwater, typically the less body fat you have, and vice versa

Body Composition vs. Weight

Weighing yourself on a regular bathroom scale does not assess your body composition. "A regular scale cannot tell how much of your total weight is water, fat, or muscle which is what body composition will tell you. This makes body composition a better indicator of health and fitness," says Walding.

"Your scale weight is a single unit of measurement and should be considered a single piece of data that is part of a much larger puzzle. Skinny does not always mean “healthy.” Low body fat does not always mean “healthy” and vice versa," explains Wilson.

For example, some people's body weight is within a healthy limit for their height, but they have very little muscle on their body and a higher body fat percentage. On the other hand, a heavier individual could have a lower body fat percentage accompanied by more lean mass.

"Body fat percentage is part of a measurement of body composition that reveals how much of the weight of your body is fat. There are normal ranges for body fat, which differ for men and women," explains Walding.

The body fat percentages considered normal are in the range of 17.6%–25.3% for males and 28.8%–35.7% for females.

Understanding Body Composition

Measuring your body composition will help you determine your body's unique makeup and help you identify areas to work on to improve your overall health and wellness.

"Two people of the same sex, height, and weight may look completely different and have completely different health issues because their composition may be vastly different. This is why looking at the composition to assess overall health or determine fitness goals should be the preferred method," says Wilson.

Body composition is a better indicator of health than the traditional Body Mass Index as well. "Body composition measurement is a clearer indicator of your fitness than BMI because body composition analysis can accurately show changes in fat mass, muscle mass, and body fat percentage. Healthy body composition includes a lower percentage of body fat and a higher percentage of non-fat mass, including muscle, bones, and organs," says Walding.

But this measurement tool also has its limits. "It’s only one area of many to consider when assessing one’s overall health and wellness. When painting a bigger picture of health, it’s best to also include blood pressure, HDL and LDL cholesterol numbers, waist size, fasting blood sugar, and triglycerides," Walding explains.

Factors That Influence Body Composition

Other factors influence your body composition, such as gender, age, and race, that you cannot control. In addition, other factors are more environmental and can be modified to change your body composition.

"Your nutrition is key, and focusing on lean proteins and whole foods like fruits and vegetables will keep you healthy. The amount of physical activity you do also plays a role, so aim to get at least 30 minutes of exercise a day," suggests Walding.

The Takeaway

When trying to get a clear, overall picture of your health, there are many factors to consider, including body composition. However, there's more complexity to health than any single type of measurement.

"I advise my Tone & Sculpt athletes to stop putting so much emphasis on what the scale says and start looking at the bigger picture—look at your own unique composition and makeup, your lifestyle, nutrition, sleep, mental well-being, and a plethora of other factors that influence your overall health and physical progress," advises Wilson.

Article Sources
Byrdie takes every opportunity to use high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial guidelines to learn more about how we keep our content accurate, reliable and trustworthy.
  1. Branco BHM, Bernuci MP, Marques DC, et al. Proposal of a normative table for body fat percentages of Brazilian young adults through bioimpedanciometryJ Exerc Rehabil. 2018;14(6):974-979. doi:10.12965/jer.1836400.200

  2. Pasco JA, Holloway KL, Dobbins AG, Kotowicz MA, Williams LJ, Brennan SL. Body mass index and measures of body fat for defining obesity and underweight: a cross-sectional, population-based studyBMC Obes. 2014;1:9. doi:10.1186/2052-9538-1-9

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