Analyzing Your Body Composition

Why body composition analysis can help you stay in step with your health and fitness goals.

Body Analysis

When you step on a scale, the numbers you see do not tell the whole story of how healthy or fit you may or may not be; a scale will display the same exact weight for a 160-pound highly conditioned athlete as it does for a 160-pound professional couch potato. The obvious differences can’t be explained by weight alone. A more accurate assessment of your body also includes characteristics such as body mass, body fat, body water and bone mass – the stuff you are made of.

Whether your next marathon involves running or binge watching, an understanding of your overall body composition, not just the pounds you are packing, will provide insight into your well-being. Many bathroom scales come with features that can help you with this, and are especially useful for tracking changes in body composition over time.

Body Mass Index (BMI)

Body Mass Index is a simple calculation derived from your height and weight: First, multiply your weight in pounds by 703. Then multiply your height in inches by itself and square the answer. Divide the number you got in the first step by the number you got in the second step. The resulting number is your BMI.

Or, you can just use our BMI calculator to get the answer faster.

Where does your BMI fall?

Low at or below 18.5
On target 18.6–24.9
High 25+

What does the BMI number mean?

The BMI is simply an expression of your height related to your weight. The BMI itself is not a measurement of your health or physiological condition. The best way to actually use your BMI information is as a screening tool. In general, the higher your BMI, the higher the risk of developing a range of conditions linked with excess weight.

A normal BMI is between 18.5 and 25; a person with a BMI between 25 and 30 is considered overweight; and a person with a BMI over 30 is considered obese. A person is considered underweight if the BMI is less than 18.5 according to the CDC.

Body Fat

Body fat weight is the weight of fat your body is carrying. It is important for the body to store certain levels of fat to function properly; however, carrying too much or too little body fat can be dangerous.

Measuring and tracking your body fat gives you another tool to monitor your overall health. For example, a person might be a perfectly healthy weight, but could be carrying too much or too little body fat. It is especially important to monitor your body fat as you exercise. Regular exercise will help you to develop lean tissue (muscle mass), which may mean you gain weight overall, but lose body fat.

How is body fat measured?

While body fat can be measured in many ways, the method used in your home scale is bioelectrical impedance. This indirect method of determining body fat starts when a safe and very low electrical current is sent through the lower half of the body. The electrical current flows more quickly through water and muscle than it will through bone and fat. The scale measures the speed of the current. Based on this number, the scale estimates body fat using a multi-step mathematical formula.

Measurements of body fat tend to fluctuate a lot more than simple weighing, and different methods of estimating body fat yield very different results. Just as different scales may give different results, different body fat analyzers can provide very different body fat estimates. Even with the same scale, the numbers may vary because:

    • Weight loss tends to produce substantial, continuous, and unpredictable changes in body water content. Because body fat analysis is determined by water content in the body, results can vary considerably from day to day.
    • Hydration status affects body fat results. If you've just worked out, there is less water in your body for the electrical current to flow through. This may result in a higher body fat reading result. In the same way, if you measure your body fat after drinking a lot of fluid, it may appear that body fat is lower than it really is.
    • Skin temperature can have an influence, too. Measuring body fat in warm, humid weather when skin is moist will yield a different result than than if when skin is cold and dry.
    • Results may not be accurate for persons under the age of 16, or persons with an elevated body temperature, diabetes or other health conditions.
    • As with weight, when your goal is to change body composition, it is better to track trends over time than to use individual daily results.

Body Water

Your body is 50%-65% water – a significant portion of your overall weight, and an important metric in your body's health. While you can shed a few pounds quickly by losing water weight, the percentage of water in your body changes daily and the loss isn't lasting. An overnight change of a half pound or more is most likely from the amount of water your body is retaining – not a sudden shift in muscle or fat.

A well-hydrated body is less likely to retain water or lose too much water. The amount of fluid needed every day varies from person to person, but maintaining a healthy level of hydration is essential to your health.

How is it measured?

The hydration level is measured by using Bioelectric Impedance Analysis (BIA). The same analysis that is used to calculate your body fat is used to calculate your hydration level. Taking into consideration a user's age and gender, a calculation is made that determines the percentage of water.

Hydration measurements should not be taken in certain situations, such as following exercise, after drinking a glass of water, or directly prior to, during, or shortly after menstrual cycles. Hydration may not be at normal levels during these times.

Bone Mass

Bone is a living, growing tissue. When you are young, your body makes new bone tissue faster than it breaks down older bone. In young adulthood, bone mass is at its peak; after that, bone loss starts to outpace bone growth, and bone mass decreases. But it's a long and very slow process that can be slowed down even more through calcium-rich diets and weight-bearing exercise.

Who should monitor bone mass?

Most people have no need to monitor bone mass, but certain groups — postmenopausal women, men and women with certain diseases, and anyone who takes medications that affect bone tissue — might want to watch for decreases in bone mass. The bone mass reading is to be used as a guide only. Watch for trends over time and contact your healthcare provider for a more detailed explanation of the readings or if you have any questions or concerns.

Benefits of Body Analysis

A body analysis scale can be a useful device for monitoring your weight loss. You should measure your body composition at the same time of the day and under consistent conditions in order to obtain the most reliable trend data. Use a body analysis scale to help stay motivated, but the best way to know how you are doing is awareness of how your clothes fit and how your body feels.