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As experts tout the many proven benefits of strength training for long-term health, longevity, and metabolic function, building and maintaining muscle continues to gain popularity as a health goal. Yet in spite of the growing interest in improving strength, many people still fixate on lowering the number on the scale — even though that number isn’t necessarily an accurate indicator of the change happening in their bodies.

A better and more effective indicator of progress is body composition.

What Is Body Composition?

Body composition refers to the percentages of fat mass and lean mass in your body; together, these make up your total body weight. Essentially, body composition tells you what makes up your body weight — and in what proportion.

Fat mass includes actual fat tissue under the skin (a.k.a. subcutaneous fat) and around your internal organs (called visceral fat), while lean mass includes anything that is not fat — think skeletal muscle, organs, bones, fluids, and waste material.

When most people say they want to lose weight, what they really mean is they want to lose unwanted fat mass and feel stronger and more toned. In almost all cases, this outcome requires muscle gain as well as fat loss. Most people are surprised to learn they can gain muscle while losing fat and still see significant changes in their body.

If your health and weight-loss plan does not prioritize losses from fat while minimizing losses from lean mass (and ideally, gaining skeletal muscle), you’re probably going to lose both. (Learn more: “Measuring Body Weight”)

Why Does Body Composition Matter for My Health?

Instead of tracking your scale weight alone, measuring your body composition provides a more accurate picture of what’s going on in your body in terms fat storage and musculature. For example, you could be a “normal” weight for your height (in terms of having a body mass index under 25) and be strong and lean and love how your clothes fit, or you could be at that same weight and have low skeletal muscle tone, underlying metabolic issues, and feel frustrated about how your clothes are fitting.

Body composition is usually reported in body fat percent, or the percentage of total weight that is made up of fat. It compares that in proportion to your total body weight. Your body fat percentage can drop from a loss of fat mass, a gain of lean body mass (since the total percentage of weight from fat would decrease), or both.

For most who are looking to feel and function better, a drop in body fat percentage is a more accurate, meaningful indicator of progress than a drop in weight. They often coincide, but not always. (There are a number of reasons why it’s expected for scale weight to fluctuate day-to-day, which is another factor as to why it’s a less informative metric than body fat percentage.)

Tracking body composition can also help you reframe your health goals. For instance, instead of losing overall pounds, you may focus on gaining muscle to increase your resting metabolic rate, the number of calories your body burns at rest.

Muscle burns about three times as many calories per pound as body fat does. So, as you drop body fat and add muscle, your scale weight might not change, but you can create a significant shift in how you look while also increasing your inherent calorie burn. (Learn more: “7 Body and Mind Benefits of Building Muscle”)

How Do I Measure My Body Composition?

You can measure body composition using skin calipers, a DEXA or DXA bone density scan, and certain advanced measures in a medical or research lab setting.

Another tool that’s highly accurate — and available at most Life Time locations — is the InBody scale, which uses electrical currents to estimate body fat and body water through Bioelectric Impedance Analysis (BIA). While there are some limitations to BIA, the InBody uses eight electrodes to send multiple frequencies through several body segments to better estimate body composition; many other machines only use one low frequency and look at a single area of the body.

The InBody can quickly analyze and provide several key data points so you can measure your progress over time. These include body fat percentage, water ratios (which can indicate inflammation and fluid retention), and skeletal muscle mass.

Want to give the InBody scale a try? Ask any Dynamic Personal Trainer for guidance on using it at your Life Time club. (Learn more: “Why This Scale Is the Best Way to Measure Progress”).

Keep the conversation going.

Leave a comment, ask a question, or see what others are talking about in the Life Time Health Facebook group.

Samantha McKinney, RD, CPT

Samantha McKinney has been a dietitian, trainer and coach for over 10 years. At first, her interests and experience were in a highly clinical setting in the medical field, which ended up laying a strong foundation for understanding metabolism as her true passion evolved: wellness and prevention. She hasn’t looked back since and has had the honor of supporting Life Time’s members and nutrition programs in various roles since 2011.

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