Body Composition

Editor’s Note: This post was updated on July 31, 2018, for accuracy and comprehensiveness. It was originally published on November 13, 2015.

“I used to be fit, but then I stopped exercising and it all turned to fat.”

Sound familiar?

It doesn’t seem like it should make sense – that muscle can turn into fat – but everyone’s seen the retired professional athlete who got really fat.

Well, here it is in black and white (and in bold): No. Muscle does not “turn into fat.” Period.

There is no process in the human body by which muscle  – which is made up of mainly protein, amino acids, and water – transforms itself into adipose (fat).  The human body, no matter how amazing it can be at times, cannot magically turn one tissue into another.

So then, what’s going on?

It’s Not Magic – It’s Body Composition

The illusion of “muscle turning into fat” becomes believable for many people when they don’t see their weight change over time, yet see themselves get fatter.  While muscle turning into fat is a myth, the possibility of your body fat percentage rising over time definitely isn’t, and that’s what’s actually happening.

So what’s actually happening? It is simply a negative change in body composition.  

Specifically, it’s a loss of Skeletal Muscle Mass combined with a gain of Fat Mass occurring at about the same rate, at about the same time.  How does this happen, and how can you avoid this? Let’s take a closer look.

Here’s what a 7-pound decrease in muscle and a 7-pound increase in fat would look like in someone who weighed 261.9 pounds with a body fat percentage of 13.0%:

Results completed on the InBody 570.

Notice how as Lean Body Mass drops, Skeletal Muscle Mass drops with it.  Because the Lean Body Mass decrease matches the Fat Mass increase, this person’s weight doesn’t change.

However, this person’s body fat percentage increased from 13.0 to 15.7.  The increased body fat percentage combined with the lack of body weight change creates the illusion that muscle is transforming into fat, when in reality it’s just an increase in body fat disguised by no change in scale weight due to muscle loss.

How do things like this happen, and why does it seem to happen to people who are or used to be very fit?  It starts with muscle loss.

Muscle Loss

Although you may not realize it, you “lose muscle” every minute you are alive.  That’s because your muscles, like any other tissue in your body, depends on cell turnover and protein synthesis.  This means that your body is continually breaking down the protein in your muscles and rebuilding them. You want your body to do this – it’s part of what’s keeping you alive!

Skeletal muscle can be grown and developed through proper nutrition – which includes consuming sufficient protein to provide the necessary amino acids – and through physical activity.  The converse is also true: if you become less physically active and/or your diet can no longer support the development of increased muscle tissue, you will enter a catabolic (tissue-reducing) state known as muscle atrophy.

Muscles that are partially used – using less than 20% of their maximum force – will start to atrophy over the long term.  Complete disuse is even worse:  muscles that are completely unused, such as when someone is bedridden and performs very little movement, can degrade by about 1/8 of their strength per week.

Of course, if you don’t have any major health complications, your muscles are not going to degrade at such a significant rate as someone who is bedridden.  However, if your body was used to operating at a high, athletic level and you suddenly stop exercising, your body won’t see any reason to maintain your muscles at that level and will begin to atrophy.

And what takes its place instead? Fat!

Same Diet, Different Lifestyle

But where does the fat come from?

The same place it always comes from: an energy surplus – caused by eating more than you’re burning.  Although for many people this isn’t exactly news, it can catch people by surprise, especially people who are used to being athletic and fit.

Athletes require massive amounts of energy in order to perform at a high level. And this energy demand requires large amounts of all major macronutrients.  In order to get that energy, they need to eat – and eat a lot. According to an interview given by Susan M. Kliner, a nutritional consultant for the Seattle Seahawks, NFL quarterbacks required somewhere between 4,000 to 6000 calories, spread out over about 6 meals per day in order to be in ideal playing shape.

A major reason why high-performance athletes like NFL quarterbacks require so many calories is that they typically have higher-than-average amounts of Lean Body Mass as compared to average people at the same height.  That’s significant because as Lean Body Mass increases, Basal Metabolic Rate (BMR) increases. BMR is the number of calories a body needs at rest, not including what is needed for movement and digesting food.

Here’s an example of someone whose body composition falls into the athletic profile:

The Lean Body Mass, SMM, and Basal Metabolic Rate was measured using the InBody 570.

Notice the high values for Lean Body Mass and Skeletal Muscle Mass.  This contributes towards the BMR value of 2,602.

However, BMR is not the total calories you need a day.  A more appropriate number is the Total Daily Energy Expenditure (TDEE), of which BMR is one part.  In order to calculate TDEE, you’ll first need to determine BMR and then multiply it by a factor determined by how active you are.  

Professional football players would fall under “extremely active” as their full-time job involves very high amounts of physical activity.  Taking the BMR in our example and multiplying it by 1.9 would result in a TDEE of 4,943.8, consistent with the statements made by Dr. Kliner.

Extremely Active: 2602 (BMR) x 1.9 (Activity level) = 4,943.8 (TDEE)

What’s important to remember is that this number is the amount of calories that this individual needs to consume maintain his weight due to his Lean Body Mass, and critically, at his current activity level.

What would happen if this person stopped being so active and took an office job – jobs that are typically sedentary?  TDEE would plummet quickly because the activity level would drop significantly.

Let’s say that this individual decided to continue being active while working at this office job and worked out enough to be classified as “moderately active.”  Assuming that BMR remains consistent, this person’s TDEE would be 4,033.1. That’s a difference of 910.7 calories, or eating approximately 22 strips of pan-fried thick cut bacon on top of what you usually eat.

Extremely Active: 2,602 (BMR) x 1.9 = 4,943.8 (TDEE)

Moderately Active: 2,602 (BMR) x 1.55 (Activity level) = 4,033.1 (TDEE)

Caloric Surplus: 4,943.8 (Old TDEE) – 4,033.1 (New TDEE) = 910.7 calories

In the example above, if this person continued to eat at the same level they did when they were extremely active, they would be in a caloric surplus of 910.7 a day, or an extra 6,374.9 calories a week.

What happens when the body remains in a caloric surplus for an extended period of time? Fat gain!

So tying it all together, it isn’t that your “muscle turns into fat.” From a body composition standpoint, here is what is happening:

• Your Lean Body Mass is decreasing due to a skeletal muscle mass loss
• Your Skeletal Muscle Mass is decreasing because of disuse. Your BMR decreases accordingly.
• Because activity level has dropped, your TDEE has also dropped.
• Energy intake remains consistent, not accounting for TDEE drop. Caloric surplus created.
• Caloric surplus leads to Fat Mass gain.

Now that we know what is happening, how do we make sure it doesn’t happen to us?

Who’s At Risk and What They Can Do

People who are at risk for gaining large amounts of fat are, somewhat ironically, people who are at their fittest right now.  That’s because when you’re at your fittest, the amount of nutrients you are consuming is necessary fuel to help the body recover after a tough workout.  You’re in balance.

The problem is, people become accustomed to eating a certain amount of food, especially when they have lived a certain way for many years.  They develop a mental understanding of how much they can eat, and they often order and/or cook portion sizes that match this mental understanding of how much food they need.

Although it is a challenge, here are three steps you can get back on track.

1. Test your Body Composition

Testing your body composition regularly is the best way to ensure that you’re staying at the level you want to be.  

By tracking your body composition, you will be able to track Lean Mass and Fat Mass gain or loss.  With that kind of information, you’ll be able to make the changes you need to ensure that you stay as fit and healthy.

2. Change your Diet

You must adjust your diet to match your current activity level, or you will risk running a caloric surplus. That change might be more than you’d expect, too.

A great way to optimize your diet is to use BMR which will make sure you are getting enough nutrients to fuel muscle growth, but also lose that stubborn belly fat.

3. Find an activity that fits your new lifestyle

Find new ways to increase your activity level that works with your current lifestyle.  Although you may no longer be performing at high levels every day, you can find new ways to be active on a schedule that works for you.

Two days of strength training a week has both great physical and mental benefits.

Remember the key is to maintain the balance between food consumption and exercise intensity that fits your current lifestyle. Once you achieve that balance, you lose the extra fat start getting your old athletic body back.

Editor’s Note: This post was updated on August 24, 2018, for accuracy and comprehensiveness. It was originally published on September 24, 2015

Consider the following three statements:

• “I’m not working out to get huge; I just want to build strength and put on five pounds of lean muscle.”
• “My goal is to workout more and put on a healthy five pounds of muscle mass before next season.”
• “I’m going to add more protein to my diet and hopefully gain 5 pounds of lean body mass by the end of the month.”

In each one, someone wants to gain five pounds of something but is using three different terms.  Are these three ways of saying the same thing? Can they be used interchangeably? Or are they different?

Let’s get one thing out of the way: “lean muscle” is a bit of a misnomer.  Although there are indeed different types of muscle, from a biological point of view, there is no such thing as “lean muscle”. The word “lean” is usually meant to suggest the absence of body fat.  But here’s the truth: all muscle is “lean muscle”.

What about Lean Body Mass and Muscle Mass?  Both of these exist. However, they are two very different parts of your body composition, and in order to understand your weight, health, and fitness goals properly, you’ll need to understand the differences between them.  Let’s take a look below.

Lean Body Mass vs. Muscle Mass

Lean Body Mass (also sometimes known as simply “lean mass,” likely the source of the word “lean muscle”) is the total weight of your body minus all the weight due to your fat mass.

Lean Body Mass (LBM) = Total Weight – Fat Mass

LBM includes the weight of:

• Organs
• Skin
• Bones
• Body Water
• Muscle Mass

Unlike lean muscle, Lean Body Mass correctly uses the word “lean” as it describes the entire weight of your body minus fat.  This is why it is also known as “Fat-Free Mass.”

Because your Lean Body Mass comprises so many parts, any change in the weight of these areas can be recorded as changes in LBM. Keep in mind, the weight of your organs will not change much. Bone density will decrease over time, but it won’t significantly affect the weight of your LBM.

Two major areas to focus on with Lean Body Mass is body water and muscle mass.

When people talk about gaining muscle by eating more protein or muscle building workouts, what they’re really talking about is gaining or building their Skeletal Muscle Mass.  This is because of the three major muscle types – cardiac, smooth, and skeletal – skeletal muscle mass is the only type of muscle that you can actively grow and develop through proper exercise and nutrition.

But Skeletal Muscle Mass is one part of your Lean Body Mass. Another major influencer is water and this can be a problem when people use muscle gain and “lean gains” interchangeably.

The Problem with “Lean Gains”

Because an increase of Skeletal Muscle Mass is an increase of Lean Body Mass, people will lump them together as “gaining lean mass” or “lean gains.”

However, it doesn’t work the other way: an increase of Lean Body Mass is not always an increase in muscle.  That’s because body water makes up a significant portion of your Lean Body Mass. To illustrate this point, here’s a body composition analysis of a 174.1-pound male.

Body Composition Analysis taken using the InBody

98.1 (Total Body Water) + 35.5 (Dry Lean Mass) = 133.6 Lean Body Mass

Water made up more than 55% of total body weight, which is normal for healthy adult males.

Notice how from a body composition standpoint, Lean Body Mass is made up of three components, two of which are water.  Everything else is grouped together in what’s called your “Dry Lean Mass,” which includes your bone minerals, protein content, etc.

Muscle gains definitely contribute to LBM gains, but so does water, which can fluctuate throughout the day depending on hydration status, diet, and physical activity.

It’s also important to note that muscle itself contains water – a lot of it.  According to the USGS, muscle can contain up to 79% water content.  Research has also shown that resistance training promotes the increase of intracellular water in both men and women.

All of this points to two main problems when talking about “lean gains”:

1. Big Lean Mass gains, when it occurs quickly, are largely increases in body water
2. It’s difficult to say with any certainty how much any gain in Lean Body Mass is due to Skeletal Muscle Mass without using the right tools

How to Measure Your Lean Body Mass and Muscle Mass

Body Composition Analysis taken using the InBody

Since there’s a significant difference between Lean Body Mass and Skeletal Muscle Mass, how is it possible to know how much of each you have?

Let’s start with what not to do: do not try to use a scale to calculate changes in Skeletal Muscle Mass.

It’s a popular method to estimate muscle gain using a combination of the number on the scale and advice from fitness magazines.

The problem with using a scale to estimate progress is there are so many factors that can influence an increase in body weight, a few of which include:

• An undigested meal or drink
• Water retention due to glycogen
• Water retention due to sodium
• Body Fat gain due to being in a caloric surplus

There is only one way to calculate what is happening to your Lean Body Mass: getting your body composition analyzed.  Without testing your body composition, there will be no way to know what any gain or loss in your body weight is due to.

Most methods of body composition analysis will at the minimum divide your body into Lean Body Mass (this may be referred to as Fat-Free Mass) and Fat Mass.  These methods include:

• Skinfold calipers
• Hydrostatic Weighing
• Air displacement plethysmography

Each of these has their pros and cons, and accuracy may vary depending on a number of factors unique to each testing method.

For more in-depth body composition analysis, you would need to look to two more sophisticated methods: dual-energy X-ray absorptiometry (DEXA) and Direct Segmental Multi-Frequency bioelectrical impedance analysis (DSM-BIA). Not only will these methods tell you how much fat you have, but they will differentiate your skeletal muscle mass from your lean body mass.

So, Lean Body Mass, Muscle Mass, Lean Mass, Which Is it?

Back to our originally three statements: which is correct to say?  Let’s review:

• Lean Muscle: You should stop using this term because it is misleading.  All muscle is “lean muscle,” and it is a confusing mix of two real terms: Skeletal Muscle Mass and Lean Body Mass.
• Muscle Mass (or Skeletal Muscle Mass): Yes, it is likely true that if you’re performing resistance training/weight lifting workouts and adding enough protein to your diet, a percentage of the change is likely due to muscle mass development. But remember that skeletal muscle mass is part of LBM. Things get tricky when you start putting numbers on your muscle mass gains. Everyone’s body composition is different, and the proportion of your skeletal muscle mass to Lean Body Mass will not be the same as someone else’s. This makes accurate estimations even harder unless you have access to sophisticated tools that can differentiate between LBM and SMM.
• Lean Mass (lean body mass):  This is probably the best and safest term to use to describe your gains.  When you use this term, you’re telling people that you have gained weight from muscle and water, not body fat.

However, that’s all you can really say.  Because of the nature of Lean Body Mass, it is very hard to say how much of the gain is due to water and how much is due to muscle (which is largely water to begin with). A gain of 5 pounds of LBM is not 5 pounds of pure muscle,

When it comes to tracking your muscle gain (or fat loss), it all comes down to what tools you’re using to measure your progress.  If all you are working with is a weight scale, then all you will ever know for sure is your weight is increasing or decreasing. It would be hard to differentiate the weight gain from water, muscle, or body fat. If you are serious about accurately measuring your muscle gain and assessing your health, go get a body composition analysis. Then – and only then – can you tell people that you gained five pounds of muscle with confidence.

How do you track your progress?

Do you keep a log of your maximum lifts and try to set personal records every day at the gym?

Every time you go out to run, do you try to run further than the run before? Do you try to run longer?

Do you weigh yourself every week, or every day? Or is your appearance in the mirror the final judge as to how much progress you’re making?

People work out for many reasons, and so there are many ways to track progress. Tracking your progress is a very good idea. It helps you stay motivated and keeps you focused on achieving your goals.  However, not all methods of tracking are created equal, and some of them are just plain bad (weighing yourself every day is a terrible idea).

No matter what your goals are in the gym or with your fitness – whether it’s gaining muscle and becoming stronger, getting toned, or simply losing fat – tracking your progress by using your body composition data is one of the best ways to get results. This means tracking your changes in:

• Body Fat Percentage
• Lean Body Mass
• Body Fat Mass
• Skeletal Muscle Mass

While almost any type of tracking can help you reach fitness goals faster, tracking the changes in your body composition allows you to do some unique things in your training that you can only do with a breakdown of your body composition.

For example…

Tracking Changes in Body Composition Lets You Turn Your “I Wants” Into Actual Goals

It’s so much easier to get results when you set goals, and it’s even easier if you set defined, numerical goals based on your body composition.

What’s meant by defined, numerical goals? Something clear, not something vague like:

• “I want to get bigger”
• “I want to lose weight.”

These aren’t goals: these are desires. They express an interest in a general, overall change in body size or shape that doesn’t allow you to measure your progress in any defined, objective way.

How are you going to assess if you get “bigger”? You can eat 4,000 calories a day and get “bigger.” You want to lose weight? You can certainly do that by cutting calories, but did you know you can also lose weight due to muscle loss? You don’t want that.

So instead, let’s take these desires and turn them into goals.

• “I want to gain 10 pounds of muscle”

Why this is better: It’s safe to assume that in most circumstances, when people want to get “bigger”, they want their muscles to get bigger, not their waistlines.  By defining your goal as being Lean Body Mass gain (muscle is the biggest component of Lean Body Mass) and putting a number to it, you have a numerical goal to work towards.

• “I want to lose 10 pounds of fat”

Why this is better: Similar to getting bigger, when people say they want to lose “weight”, it’s safe to assume that they really want to lose fat.  You don’t want to lose muscle – muscle is metabolically active tissue that serves many important roles: from maintaining your metabolism to supporting healthy bone density to keeping a healthy immune system.

It’s likely that some muscle loss will occur when you try to lose fat, so by monitoring the changes in your body composition, you’ll be able to keep an eye on this and minimize any losses that may occur by making the necessary corrections in your diet and exercise program.

Tracking Changes In Your Body Composition Lets You Set Reachable Time-Based Goals

Sometimes, you start a fitness journey because you have a special event coming up. Maybe you’re going on a vacation and you want to have a rockin’ body when you hit the beach.  Maybe there’s a wedding coming up, and you want to make sure you fit into a new/favorite dress.

Point is: there’s a deadline you want results by, and you want a solution that will help you get there. This is a really common situation, so common that nearly every fad diet or gimmicky product makes time deadlines a critical part of their marketing. These diets and products all claim to solve an immediate problem, which makes people feel better, and which is why popular magazines just love promoting them (looking at you, Cosmopolitan).

There are no shortcuts to losing weight, gaining muscle in a very short amount of time. But instead, by tracking your progress by tracking your changes in body composition, you can actually set real goals with real results that you can actually achieve.

Let’s build on the goals we made before, this time adding a reasonable time frame.

• “I want to build 10 pounds of muscle in 5-6 months”

When you try to build develop muscle and Lean Body Mass, there are a lot of factors that go into whether or not you achieve that goal.  What type of exercises you do, the degree to which you properly perform your exercises, whether you lift heavy with few reps or light with many, how often you strength train, how often you rest…the list goes on, and that doesn’t even include proper nutrition.

However, assuming that you do everything perfect and you’re a beginner, experts posit that you can gain roughly 2 pounds of muscle a month with consistent, proper training. If you’re not a beginner, your rate of lean mass growth will be slower as you get closer to your genetic limit for natural muscle development.

Knowing this, if you’re just getting started, you can track your progress every month and expect to see around a 2-pound increase every month until you reach your goal of 10 pounds of muscle by following a challenging lifting program.

Here’s what this can look like over 5 months:

When you use your body composition to track your progress, it suddenly doesn’t matter as much how much you can lift, or how many reps you can do. Instead, what matters is that you’re working towards a physical goal – getting bigger and more muscular – and you’re doing it in a way that you can reliably track towards a realistic goal.

• “I want to lose 10 pounds of fat in 10-12 weeks”

In some ways, losing Fat Mass is easier than building Lean Body Mass and muscle.  There are many types of exercise that encourage Lean Body Mass development, many workout plans to organize them in, and it requires significant amounts of rest and recovery. Fat loss, on the other hand, requires less arguably less planning and actually occurs faster than muscle gain.

To lose Fat Mass, you need to be in a caloric deficit (taking in less calories than you use) and maintain it carefully over an extended period of time.  This isn’t rocket science, and virtually every peer-reviewed study that includes groups that undergo a caloric deficit experience fat loss. Here are three published in 2015 alone. Hypocaloric diets work.

How quickly can you lost fat? Many studies and health groups, including the Centers for Disease Control, report that by reducing your caloric intake by 3,500 calories a week typically results in a pound of fat loss.

Here’s what that can look like over 12 weeks:

Note: a pound of fat loss, not weight loss.  If you’re just a scale to measure your rate of change, you may experience even more “weight loss,” but if you’re on a hypocaloric diet, especially one that focuses on cutting out carbohydrates, you might experience additional water weight loss.

That’s because water bonds to glycogen at rate of about 4 grams of water: 1 gram of carbs. If you’re much lower on carbs than you usually are, you’ll be retaining less water and weigh less accordingly.

When you use your body composition to track your progress with fat loss, you can account for what’s actually being lost when you see your weight decrease on the scale. This helps you avoid mistaking your weight loss for water weight loss or (hopefully not) muscle loss.

Why is this important to know? If you’re tracking your body composition changes instead of simple scale weight changes, you won’t be confused when you gain a few pounds back after reintroducing carbs into your diet.  You’ll know that this weight is water, not fat.

Also, by being patient and tracking a pound or two of fat loss each month, you can stay motivated by knowing you’re making real changes that will last in your body. Gaining water weight is as easy as refueling on carbs, but gaining actual fat? That requires you to be in a caloric surplus over a period of time.  Eat within your Total Daily Energy Expenditure, and you can expect your fat mass to remain stable.

Tracking Changes In Your Body Composition Helps You Reduce Negative Changes In Your Body

Unfortunately, the truth is that “positive” results– increases in muscle and decreases in fat – usually come paired with negative consequences.

• Gaining Fat With Muscle

If the results you’re working for are muscle gain, you may end up experiencing some unwanted fat gain as a side effect.  This is due to the nature of the diet you should go on to encourage muscle tissue growth: namely, a caloric surplus.

Getting sufficient nutrients/calories – particularly carbohydrates and protein – is essential for encouraging increased muscle and strength. However, just as eating fewer calories than you use causes a decrease in fat, eating more than your body “needs” will cause a gain in fat over time.

For some people, gaining a little extra fat is not a big concern, but for others it is – especially if clothes start to not fit properly.  By tracking your body composition changes, you’ll be able to track both muscle and fat gain, allowing you to change your diet or exercise routine if you feel that you’re gaining too much fat.

• Losing Muscle With Fat

The opposite is true when you try to lose fat. With large reductions in fat due to a hypocaloric diet, you can lose Lean Body Mass and Skeletal Muscle Mass.  Muscle is healthy tissue that you should work hard to preserve.

Fortunately, you can minimize the loss of muscle while reducing fat mass by increasing your protein intake and by performing resistance training. In a study of overweight police officers, the group that ingested casein protein supplements and performed regular resistance training experienced less loss of muscle tissue and increased strength vs. the group that simply dieted.

By tracking your body composition changes, you’ll be able to keep an eye on any losses in muscle development.  Just like for people who want to build muscle, if you see that your negative change – loss in muscle – is becoming too great when you track your body composition changes, you can made the necessary adjustments to your diet and workout plan to help mitigate that loss.

Tracking Progress and Setting Reachable Goals Leads to Success

Tracking your progress over time is one of the most important things you can do to ensure your reach your health and fitness goals.  Whether that’s gaining muscle, losing fat, or both, by accurately tracking your progress with something measurable instead of something visual – like a mirror – or unreliable – like scale weight – you will be able to reach your goals faster.

That’s why tracking progress with your body composition delivers results: it offers objective, measurable values in your body that translate into physical results.

With more muscle and less fat, you’ll be stronger, look fitter, and will be healthier. You’ll be able to gauge this progress objectively instead of guessing, and you’ll be able to make smart adjustments in your training as needs be.

Doesn’t that sound nice?