If you’ve ever wondered how much of your body is made up of fat, you’ve likely turned to the Body Mass Index. It’s a calculation of your body fat based on your weight-to-height ratio.
Unfortunately, it’s woefully dated and an inaccurate means of establishing if you’re over or underweight. But what to use instead?
A Body Composition Test
A body composition test determines how much of your body is made up of fat and fat-free mass. Your body fat is responsible for storing energy while fat-free mass (made up of muscles, water, bones and organs) is responsible for burning calories.
A body composition test can give you the insight you need to make targeted adjustments to your diet and exercise regime.
A body composition test provides a better estimate of fitness and health than the Body Mass Index because it takes more than just weight and height into account. Doctors, like me, can learn so much more about you by putting you on an analyzer and running a painless, imperceptible electric current through your body. Understanding the composition of fat and fat-free mass in your body helps us to determine if you need to build more muscle or lose fat.
A body composition test can also reveal certain underlying health issues and give you the insight you need to make targeted adjustments to your diet and exercise regime.
In my medical practice, I use the InBody 720. Body composition analysis takes all of two minutes and allows me to quickly learn about a patient’s body in comparison to others their age, height and sex. The analysis calculates several factors not included as part of the body mass index, including:
- Lean body mass (LBM) as a percentage of the ideal in each limb and in the trunk
- The level of extracellular and intracellular water in the body
- Basal metabolic rate (BMR) which indicates how many calories the body burns per day without movement or exercise
How the Test Measures Are Used
Based on calculations from the test, your doctor will assess how much fat or muscle you need to gain or lose. Lean body mass, or LBM, is everything in your body that isn’t fat. It’s a decent estimator for your level of muscle mass compared to the ideal for your age group. If your lean body mass is below expected, chances are your doctor will recommend that you incorporate strength training into your exercise regime.
For patients recovering from an accidental fall or stroke, a body composition test can also objectively gauge your level of recovery compared to your baseline.
Athletes routinely use body composition to monitor their level of muscle mass. For instance, if their arms look light for their size, an athlete will focus on strengthening them, especially if doing so could give them a competitive advantage.
But sarcopenia, the fancy word for losing muscle mass, can also be measured using this method. For older adults, monitoring muscle mass is especially important because sarcopenia is a common condition that can contribute to functional decline and loss of independence. In my experience, when a patient sees actual numbers on the machine, like those telling them to gain 5.6 pounds of muscle, it’s empowering.
Louisa Flinn, Certified Personal Trainer and founder of Lifetime Daily agrees. “As individuals age, body composition changes. Fat mass can increase and muscle mass can decrease. This can happen even in the absence of changes in your body weight. A body composition analysis can provide information that makes changes in your routine worth the effort.”
Personal trainers and nutritionists also use basal metabolic rate to calculate calories for individualized nutrition plans, and the water measurements can tell us if you’re retaining water, which is a marker for something worrisome like liver failure or dehydration.
A body composition test can also reveal potential health issues. In one case, a runner patient’s body composition test results didn’t make sense to me at first. Her basal metabolic rate was quite high, indicating a robust amount of muscle on her body (more muscle equals higher metabolism). Her arms and legs were above the expected lean body mass for her weight, yet the machine recommended she gain quite a lot of lean body mass.
I realized then that she was running so much that her menstrual period had stopped, and she was showing early symptoms of osteoporosis at a very young age. Her estrogen was so low from her low body fat that it was affecting her bone mass. While she had plenty of muscle, she needed to build bone. Her bone density must have been compromised in her spine, leading to the unusual test results.
What to Know Before Taking the Test
If you’re interested in taking a body composition test, speak with your doctor during your next visit. Though know that body composition tests that use electrical impedance haven’t been validated as safe for patients with electrical devices like pacemakers. Also, you should only take a body composition test after fasting for at least two hours, with an empty bladder and once you’ve removed all metal near your body, like jewelry and underwire undergarments.
If you meet the Centers for Disease Control’s physical activity guidelines of 150 minutes of moderate-intensity aerobic activity per week in addition to two 30-minute-long strength training sessions, a body composition test is a great way to compare yourself to the ideal for your age group. If you don’t meet the requirements, the results of your body composition test may be the motivation you need to get moving.
Editor’s note: The writer, Monya De, does not have a financial interest in the InBody 720.
