What Are You Made Of? – Body Composition

Several metal panels peek out of the museum floor. “Your Weight On the Moon” proclaims one. You remember of the footage of astronauts hopping effortlessly on the lunar landscape. Other bear the labels “Your Weight On Jupiter” and “Your Weight on the Sun,” each scale tweaked to show the effects of gravity. Now, no one here is walking on the sun any time soon; however, the scales at the Rose Center for Earth and Space prove an important fact.
Your body didn’t magically change when you hopped from one scale to the other. You still had the same bones and organs and muscle and fat, but the “gravity” changed the number on the scale. It’s a little bit of a flashback to weight versus mass in middle school science.
Why are we talking about the planetarium on a fitness blog? Well, it’s because of those scales. For many of us, the scale is the number we live and die by when we want to get healthier. “Lose Weight” is one of the most common ways people say they want to get fitter. So, seeing that number on the scale carries an elevated importance. For some people, ‘undesired’ changes in that number can cause a lot of emotional turmoil and stress.
But I’m here to tell you that the scale is only showing you part of the picture.
If you want to see a lower number on the scale, you could go to the moon. But it doesn’t actually impact your health. Which brings me to today’s topic: body mass and body composition. We’re going to talk about what makes up our bodies, how we measure body composition, and how to reframe progress.
Olympic Athletes 2000-2002

Photo by Howard Schatz.

Body Composition

When we look at body composition, we look at four key elements: Water, Bone, Muscle (known as lean mass), and Fat. Every one of those plays a vital role in how our bodies work and function, so let’s take a quick dive into each of these.


After a few weeks of steady progress — dialing in your nutrition, nailing your workouts — you get on the scale. Somehow you’ve gained three pounds overnight. What the heck!? You’ve been doing everything right!e you’re just not meant to be lean, you think; you wonder if all this effort is worth it. Raise your hand if you’ve been there before.
Water is the easiest component of our bodies to manipulate, especially since it makes up 50-60% of our mass. A quick jump on the scale is almost definitely due to water. (Not So) Fun Fact: those diet teas you see sold online that help you lose weight? They’re mostly diuretics that make you pee and poop to get extra water our of your body. Yuck.
So, what causes these sudden jumps? Sodium, Carbohydrates, and Hormones are the most likely culprits.
The body needs to maintain a balance of electrolytes in the blood stream. A restaurant-made meal may have way more salt than you’re used to having. So, your body will hold on to more water than it typically does to keep that balance in check. This will absolutely show up on the scale, and possibly in your clothes as well via bloating.

Back in our Carbohydrate Profile we talked about how our bodies store glycogen as a quick energy source. However, for every gram of glycogen our bodies store, we store three grams of water to go with it. A high-carb meal the night before a race can be a great way to make sure your body has the fuel it needs to keep going. But if you’re looking at the scale the morning after a pasta dinner, that water will make a difference.

Hormonal changes are constantly being studied by scientists around the world, so our understanding is still evolving. But one thing we know for sure is that high levels of estrogen correlate with water retention. So, for anyone who menstruates and has experienced up to 5 lbs of weight variation, that’s pretty much the answer right there.


While bone mineral content only makes up 3-5 percent of our body mass, a little goes a long way. There’s no denying that providing the physical structure and support for our bodies is a very important job. But, once we hit adulthood, there’s not much that’s going to change the mass of our bones — outside of the aging process.

The rate at which bone mass changes is largely based on genetics. Most people reach their peak bone mass around 25-30 years old, and by around 40 can begin a slow decline. Not only does that take away our body’s calcium reserve, but it also leaves you open to a greater risk of fractures and breaks. Bone loss can be slowed by proper nutrition and weight-bearing exercise.


Generally when people think about muscle they think physique — big and bulky or lean and toned. But the muscle in our body does so much more than make us look good. We also have blood-pumping cardiac muscle, and smooth muscle tackling involuntary internal movement.
Mobility, balance, and strength are essential to everyday wellness. That’s why maintaining muscle mass is important — especially in older populations. In fact, total lean body mass seems to be the key to maintaining bone mineral density as we get older. As you get older, hormonal changes may make it harder to put on muscle. And, in general, it’s easier to prevent muscle loss than start from scratch. But, it’s never too late to get started.

And, if you’ve been getting into resistance training for the first time, you may be perplexed as to why the scale hasn’t changed. There are two reasons I can think of right off the top of my head.

First, is the one we all know — muscle is denser than body fat. No, it doesn’t weigh less. A pound of fat and a pound of muscle are both still a pound. But it takes up less space on your body. Check progress photos, or measurements, check how your clothes fit and you may be surprised that there are changes the scale can’t tell you.

Second, the day after a very hard workout can lead to some serious fluid retention. Delayed onset muscle soreness or DOMS is the pain you feel the day (or 2 days or 3 days) after a particularly strenuous workout. Currently believed to be caused by small tears to the muscle, DOMS will lead to an increase in fluid retention as your body works hard to repair those muscles to make them stronger. DOMS can be particularly pronounced in people just starting an exercise routine.

Body Fat

Emerging research on body fat, also called adipose tissue, shows that it’s not just a lump of lipids that sits there, but a critical part of the endocrine system. Body fat plays a large role in the function of estrogen (yes, in all humans), cortisol (the stress hormone), insulin (the blood sugar hormone), growth hormone, and leptin (the hunger hormone).

According to the National Academy of Sports Medicine, where I got my training certification, there is a range of adipose tissue that is considered essential and beneficial. For people whose predominant sex hormone is testosterone, the recommended range is between 8 and 25%, and not below 3-5%. For people whose predominant sec hormone is estrogen, that range is a little higher from around 12-35% and not below 8%. What is healthy and beneficial for you may vary based on genetics, but these are a few guideposts to help you explore what works for you.

Above those ranges, excess adipose tissue can begin to cause problems. Because adipose is an active part of the endocrine system, it has a direct role in producing adipocytokines. Basically, that’s a lot of syllables to say “molecules that send signals to cells.” Unfortunately, a lot of those molecules end up creating a pro-inflammatory environment within the body. The stress that this state puts on the body increases the risk of cardiovascular disease, diabetes, and even cognitive decline.

As a percentage of the population, fewer people are at risk of the complications of being underfat; however, those risks are no less dangerous. Whether it’s caused by an eating disorder, wasting from chronic illness, or lack of access to food, not having enough body fat will also lead to hormonal dysregulation and often coincides with malnutrition leaving the body in a vulnerable state.

So, when it comes to body fat, we generally want that Goldilocks spot — not too little, not too much, just right for supporting our health and our goals.

Measuring Body Composition

Body Mass Index

I’m sure most of us are familiar with BMI. It is a simple, guideline tool, but it can be inaccurate. Terry Crews, for example, is 6′ 3″ and 245 lbs. He clocks in at 30.6 on the body mass index, which is just over the cut off for “obese”. However, Terry Crews also has 4% body fat, and is likely not at risk of health complications of being overfat. In his case, this is inaccurate because it has overestimated his body fat percentage.

However, the most common inaccuracy of the BMI is that it often underestimates adipose tissue. This study by Nirav R. Shah and Eric R. Braverman plotted the BMI versus the body fat percentage of 1400 individuals and found interesting results.

Scatterplot of Body Mass Index vs Body Fat Percentage of almost 1400 individuals. For 60% of the patients, their BMI and body fat percentage reflected the same results. 1% of the patients showed the Terry Crews problem of being overweight by BMI but had a low body fat percentage. However, a full 39% of participants had a higher body fat percentage than their BMI would indicate.

What it really boils down to is a massive change in the way people live their lives. The BMI was developed in the mid-1800s, a period of time that didn’t have our accessibility of food and required a lot more physical work throughout the day. Far more physical labor went into simple tasks like going to the store or washing laundry. While it seems simple, the combination of less convenience food and more physical exertion lead a populace that generally used more energy on a regular basis and consumed less than we do today.

Body Measurements & Ratios

Probably the simplest way to see changes in body composition is through measurements — whether you want to grow your biceps or whittle your waistline. All you need is a tape measure and a piece of paper to write down some numbers. These changes can be slow, so I don’t recommend doing body measurements more than once a month.

These measurements can also be plugged into a few different formulas like the Army Body Fat Calculator. Take this with a grain of salt, these are based on averages and may be a bit off from your actual percentage.

You can also look at measures like the waist-to-height ratio. While not a measure of body composition per se, it does take into account the amount of visceral belly fat around the stomach and waistline which can be a big contributor to health issues.

Skin Fold Calipers

Calipers can measure your subcutaneous fat by measuring the millimeters of a pinch of fat. Usually, a skinfold test will take a few measurements and plug them into a formula to find the result. You may want a friend to help you take the measurements because some of the areas can be hard to reach on their own.

While this can be an accurate test, it takes someone skilled and knowledgable to ensure accuracy.

Bio-Electrical Impedance Analysis (BIA)

If you’ve ever gotten on a scale with metal sensors that measures body fat, or tested with a hand-held device, then you’ve experienced BIA. BIA works on the idea that electricity will travel at different speeds through lean mass versus fat mass. It is a quick and widely available method of calculating body fat percentage, but it struggles not only with accuracy but precision.

The amount of food in your system or your hydration levels can drastically shift the calculations, which means variation on a day to day basis. An inaccurate but precise tool (like the BMI) can help you at least track trends. But BIA isn’t even precise, so using it to track long term trends can be a challenge.

Hydrostatic Weighing and Air Displacement Plethysmography

These two tests estimate your body fat percentage based on your density. They tend to be more accurate than the previously mentioned tests, but that comes with a catch. They require specialized equipment and are more expensive than some of the other options, meaning it takes time and money to seek them out. However, once the test begins, they only take a matter of minutes.

And, if you have a fear of closed spaces these may not be for you. The first test requires being fully submerged under water and the other requires being enclosed in an egg-shaped pod. I tell my clients that it looks like an alien egg.

Dual-Energy X-ray Absorptiometry (DXA or DEXA)

A DEXA scan takes approximately 10 minutes, as you lie on your back and get scanned by, well, X-rays. The scan provides very detailed information, giving feedback on bone, muscle, and fat mass. Your results are also broken down by arms, legs, and torso. I’ve had this scan done before and being the data nerd I am, it’s very informative.

It’s also pretty expensive and hard to come by as most DEXA scans are done in medical settings. However, there are more and more companies, like DexaFit, that are providing this service.

Body Composition & Fitness Progress

Progress. It’s the confirmation that all the effort we are putting into our fitness and nutrition is working.

Now that we know the scale doesn’t give you a full picture, it seems really tempting to just shift focus to body composition as that signal that you’re succeeding. And for some people, this concept can be gratifying and freeing. They can look at numbers and see them as data points and move on, this is especially true for athletes and people competing in weight categories for their sport. But for others, those numbers can become as stressful and controlling as the numbers on the scale.

As we work towards new fitness goals, it’s important to frame progress as more than the numbers on the scale. If you really dig into why someone wants to get in better shape, the root of it is rarely about quantifying our bodies. The heart of getting fitter is adding more quality to our lives.

Here are some real world signs of progress that you may not even notice.

  • You can carry all of your groceries in one trip. (My actual favorite part of strength training)
  • You can bend over, crouch, and squat down with ease.
  • Taking the steps no longer takes your breath away.
  • You sleep better at night.
  • You feel more alert during the day.
  • You’re having fewer cravings for processed food.
  • It’s easier to play with your kids/nieces/nephews/dog.
  • You get sick less frequently.
  • You have less knee, hip, or lower back pain.
  • When you dance like nobody’s watching, keep going and going.
  • You can do more reps with the same weight.
  • You get excited about going for a walk or a hike.
  • You’ve stopped stressing over the scale.

And that last one is a huge one. It can take some time, some mindfulness, some positive self-talk. But when you can look at your body composition in terms of matter and remember that, regardless of any measurement, you matter, it is the best breath of fresh air. Instead of punishing yourself for how you look, think about all the ways your body supports you. Then try to support it right back.

In the end, the goal is a balance. And body composition is part of it, but it is only one part.

Did you find this article helpful? Are you feeling just a little bit better in your skin? Make sure you share with someone who needs to hear it, too.


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