Editor’s Note: This post was updated on October 16, 2026 , for accuracy and comprehensiveness. It was originally published on March 25, 2016.

You track body composition because it answers the one question the scale can't: is the weight you're gaining or losing muscle or fat? A number on the bathroom scale lumps muscle, fat, water, and bone into a single figure, so it can move the wrong way for the right reasons, or the right way for the wrong ones. Tracking your body composition splits that number apart and shows you what's actually changing.

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…

It Turns Vague Wants Into Real 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.

It Lets You Set Deadlines You Can Actually Hit

Sometimes, you start a fitness journey because you have a special event coming up. . Maybe a vacation is coming up and there's a target date attached to it. 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 or 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 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 everything is done correctly 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, arguably requires less planning and tends to occur faster than muscle gain.

To lose Fat Mass, you need to be in a caloric deficit (taking in fewer 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 undergoing a caloric deficit reports fat loss. Here are three published in 2015 alone. Hypocaloric diets work.

How quickly can fat loss occur? Many studies and health groups, including the Centers for Disease Control, report that reducing caloric intake by 3,500 calories a week typically results in about 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 using 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 a rate of about 4 grams of water per 1 gram of carbohydrate. 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.

Tracking a pound or two of fat loss each month also distinguishes gradual fat change from short-term water shifts. Water weight can return quickly with carbohydrate intake, while fat gain generally requires a caloric surplus sustained over time. Eating within Total Daily Energy Expenditure is generally associated with stable fat mass.

It Catches Fat Gain and Muscle Loss Early 

Positive" results, meaning increases in muscle and decreases in fat, often come with trade-offs.

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 commonly used 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 metabolically active tissue, and preserving it is generally a priority during fat loss.

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.

The sThe same tracking that identifies unwanted fat gain also identifies unwanted muscle loss, allowing adjustments before either becomes significant.

How Often Should You Track Body Composition?

For most people, every two to four weeks. Body composition changes slowly, so meaningful shifts in fat and lean mass take a few weeks to show up. Testing daily mostly captures water-weight fluctuation, the same limitation as the scale.

Typical intervals by goal:

• Actively losing fat or following a new program: every two weeks, since you'll often see a change within one to two weeks and want to catch what's working

• Building muscle: every three to four weeks, since lean mass builds slowly and needs time to register

• Maintaining: every couple of months is generally sufficient

Consistency of conditions matters as much as the interval. Testing with the same method, at a similar time of day, and under similar hydration makes results more comparable over time. Testing method also affects frequency: methods that require radiation exposure or a scheduled appointment are generally limited to a few times a year, while a test that takes about a minute can be repeated at shorter intervals.

The Takeaway 

That’s why tracking progress with your body composition delivers results: it offers objective, measurable values in your body that translate into physical results. Tracking the values that separate muscle from fat, at an interval suited to the goal, provides a clearer picture of whether an approach is working.

Frequently Asked Questions

Why track body composition instead of weight?

Weight is a single number that can't tell muscle from fat from water. You can lose ten pounds and lose muscle, or gain weight and lose fat, and the scale reads both the same. Body composition shows which is happening.

How long before I see body composition changes?

Most people on a consistent program see measurable change in two to four weeks. Fat loss and muscle gain are both gradual, which is why measurable data is more reliable than estimation.

Can your weight stay the same while your body composition improves?

Yes, and it's common. If you lose fat and build muscle at a similar rate, the scale barely moves while your body is changing underneath. This is a case where body composition data is more informative than weight alone.