Body Composition

Body Composition: Definition and Insights Into Health

Body composition is the term used in the fitness and health community to refer to the percentage of fat, water, bone, muscle, skin, and other lean tissues that make up the body. 

While checking your weight on the scale can be helpful for seeing your total weight, it doesn’t tell you how the weight is distributed in your body.

Body composition is typically broken up into two groups:

• Fat mass refers to the body's stored fat. Fat insulates the body, surrounds your organs, and is used for energy.
• Non-fat mass refers to all of your body's components except fat. Non-fat mass includes bones, liver, kidneys, intestines, muscles, and other organs and tissues your body needs to function.

Many health risks are tied to the ratio of fat mass to non-fat mass. Research shows that the risk of premature death is greater in people who have higher percentages of fat compared to non-fat mass.

In comparison, people with higher percentages of non-fat mass compared to fat mass tend to be leaner with more muscle. These individuals have a lower risk of many diseases

Importance of Measuring Body Composition

Body composition is a valuable tool for assessing:

• Health status: Body composition assesses the percentage of fat in the body. Having excessive body fat, especially fat around organs (visceral body fat), increases the risk of many health conditions, including heart disease, diabetes, and several cancers.³
• Fitness levels: Athletes and fitness enthusiasts can use body composition as a tool to track their lean muscle-building progress. Body composition helps athletes optimize their strength, endurance, and overall athletic performance.⁴
• Nutritional status: Body composition can help you and your healthcare provider understand if you have too much or too little body fat relative to your weight. This information can be used to design a safe and effective diet intervention or meal plan.¹
• Metabolic health: Having excess fat increases the risk of metabolic health issues, including insulin resistance, imbalances of cholesterol and triglycerides, high blood pressure, uncontrolled blood sugar, and slowed metabolism. Body composition is therefore an effective tool for monitoring and reducing these risks.⁵
• Weight control: Weight loss is often accompanied by a loss in lean body mass, especially muscle, which can impede long-term weight loss by slowing metabolism and increasing fatigue. Monitoring body composition helps maintain lean body mass while also shedding body fat.

Body Composition vs. Weight and Body Mass Index

BMI is a screening tool commonly used to assess a person's weight in relation to their height. The tool provides a general evaluation of a person's health risks relative to their weight. But, unlike body composition, it does not provide specifics about the distribution of a person's weight.

BMI is calculated by taking total body mass in kilograms (kg) and dividing it by height in meters (m) squared. The results are written as kg/m2.

The number is then put into a chart to find the category. The BMI categories include:⁷

Centers for Disease Control and Prevention. Adult BMI categories.

• BMI less than 18.5 = Underweight
• BMI 18.5 to 24.9 = Normal
• BMI 25 to 29.9 = Overweight
• BMI 30 to 34.9 = Obese class I
• BMI 35 to 39.9 = Obese class II
• BMI more than 40 = Obese class III

Whereas BMI measures weight relative to height, body composition measures fat in proportion to lean body mass. For this reason, body composition offers a more accurate and comprehensive insight into a person's overall health.

Take, for example, an athlete with excessive muscle and very little fat. This individual will likely have a high BMI. In this instance, though, having a high BMI does not mean they have obesity or a greater risk of health conditions that are associated with obesity.

In order to get an accurate evaluation of how much fat, muscle, and all-around lean mass this individual has, an evaluation of their body composition is needed.

Calculating Body Composition

Bioimpedance Analysis 

A bioimpedance analysis (BIA) uses a painless, low-energy electrical current to assess fat mass, muscle mass, and hydration (water mass). 

Muscle contains more water than fat, so it conducts the energy current better than fat. Fat tissue impedes the movement of the current. The BIA scanner can assess body composition based on how the energy moves through the body. This test tends to cost less and may be easier to find than other types of scans.

However, the accuracy of this assessment changes based on how hydrated you are. If you drink too much water before the test, you could appear leaner than you are. If you’re dehydrated, the test may say you have more body fat than you do.