How Do Muscle And Fat Affect Your Weight?

If you’re trying to lose weight, the chances are that you have a “goal weight” in mind. 

With so many of our conversations about health centering around factors like obesity, sedentary lifestyles, and overall fitness, it seems that we’re always looking for ways to get healthy and reach what we believe is our ideal weight. 

After all, the best way to make sure that you actually reach a goal is by making it measurable in the first place, and your weight is a great way to see how much progress you’re making. 

But what’s going on beyond the scale?

There’s a lot more to being healthy than just knowing how much you weigh. Your weight can be a crucial indicator of your health, but that final number might not show you the whole picture.

If you want to talk about weight (or weight loss), it’s vital to have a solid understanding of the two most significant contributors to your weight: muscle and fat tissue. 

The Two Different Tissues Contributing to Your Weight  

There are a couple of components that make up your body weight, but the two types of tissue that can be the biggest indicators of your health and fitness: muscle and fat. 

Let’s Talk About Muscle 

Your muscles are the tissues in your body that are responsible for strength and movement. They also help to support your bones and contribute to your energy metabolism. 

There are three different kinds of muscle: 

When it comes to body composition and body weight, we’re mostly talking about Skeletal Muscle Mass. Theseare the muscles that you can typically change through a combination of a healthy diet and exercise. Traditionally, we work out and grow these muscles (or neglect them and let them atrophy). Think biceps, triceps, abdominals, glutes, etc.  

What About Fat?  

Fat, also known as adipose tissue, is another major contributor to your overall body weight – and it’s often the one that people are looking to get rid of when they talk about weight loss. 

There are two different kinds of fat: 

Despite the negative connotation, having a certain amount of fat tissue is actually necessary. Your body stores unused energy from your food as fat, so it can provide a reliable source of fuel when you need it. Fat tissue also acts as insulation to keep you warm and as a “cushion” to protect your vital organs. 

Finally, fat is an endocrine organ, which means that it plays a role in releasing hormones and regulating your blood sugar

The visible problem is excess body fat, which can lead to higher body weight and altered hormone release that can make the condition worse. 

How Muscle And Fat Contribute To Your Body Weight

When it comes to weight, most of the focus is on body fat and muscle because they can both be controlled (and changed!) by your lifestyle

Your Body Fat Mass (or the amount of fat you have in your body) is highly variable based on your diet and exercise. Since one of its primary functions is energy storage, your Body Fat Mass can change depending on whether you’re eating at a caloric deficit or caloric surplus. 

This means that if you are at a caloric surplus, or eating more than what your body uses, the excess energy can be stored as fat, which leads to weight gain. 

You also have a lot of control over how your Skeletal Muscle Mass contributes to your weight since these are the muscles that can grow with exercise. Because of this, the amount of muscle mass you have can be an indication of your fitness. 

Does Muscle Weigh More Than Fat? 

Not only do these two tissues have different functions, but they also take up space in your body in very different ways. 

You may have heard the phrase “muscle weighs more than fat” before. What this means is that, while a pound of fat is going to weigh the same as a pound of muscle, they’re going to look very different. 

Muscle tissue is denser than fat tissue, so a pound of muscle tissue takes up much less space than a pound of body fat. This means you can be the same height and weight as someone else but look completely different and have different body composition because of the different body fat-to-muscle ratios—and this can also mean that the healthiness of your weight can vary. 

Why Knowing Your Body Composition Is Just As Important As Your Weight

When it comes to determining their “healthy weight range,” a lot of people put the focus on their BMI, or Body Mass Index, which uses a general formula to decide how your weight compares with your height. But these two numbers don’t necessarily give you the whole picture of your health since it doesn’t show exactly how your muscle and fat contribute to that weight. 

Take this study, for example: while evaluating the weight and body composition of college athletes, researchers found that 38 of the subjects had BMIs indicating that they were overweight, but only 4 of those subjects actually had excess body fat. This means that a higher Skeletal Muscle Mass may classify you as overweight on the scale! 

There is more to your health and fitness than your body weight alone. 

Understanding Your Body Composition

To understand how the weight on the scale relates to your body composition, you have to understand that your weight is broken down into Body Fat Mass and Lean Body Mass and where Skeletal Muscle Mass fits into that mix.

The definition of Lean Body Mass is your total body weight minus your Body Fat Mass, which leaves your Skeletal Muscle Mass as well as the weight of your organs, skin, bones, and body water. This measurement can give you an idea of how much of your body weight is made up of fat and muscle. 

Not only is this important for having a grasp of how healthy you are, but it can also help with your metabolism, which can then go on to help you with any body composition or weight loss goals you may have. People who have more Lean Body Mass use more calories every day when they’re at rest to maintain those muscle tissues, so having a higher muscle mass is actually beneficial for using more calories daily and burning fat. 

And on the flip side, excess body fat can pose health risks like heart disease, high cholesterol, and metabolic syndrome, even if you have a normal BMI

You Can Improve Your Health Regardless of Your Weight  

The right balance of Lean Body Mass and Body Fat Mass can help you to maintain your health and your capacity for functional movement outside of weight alone and is generally a better indication of your overall fitness. 

The really good news about this is that it means weight loss on its own isn’t always the end-all-be-all of improving your health and quality of life.

For example, one study found that patients improved their knee pain by lowering their body fat percentageand increasing their activity, even when their body weight didn’t change significantly. 

Key Insights for Goal-Planning


Knowing your body composition can give you vital insights into just how healthy you are—and that can mean a more clear path for making the right decisions for your health and fitness. 

Having a “snapshot” of your Body Fat Mass and Skeletal Muscle Mass—and how both of those components contribute to the final number on the scale—can help you determine what steps you should be taking to improve your overall body composition and health. 

For example, if you find that your Body Fat Mass is high, but your Skeletal Muscle Mass seems to be in a normal range, you can focus more on cutting your fat through a combination of exercise and diet rather than just resistance training to build muscle.

This can also help you see that your progress doesn’t always show on the scale! If you’ve been hitting the gym hard and are feeling a lot more fit, but the scale hasn’t moved, you might be building muscle. Again, muscle takes up less space in your body than fat tissue, so this progress won’t necessarily show on the scale, but it doesn’t mean that you aren’t making any progress. 

Getting a body composition test lets you learn more about your body composition and can show that you’re building muscle to keep you motivated to continue. 

How To Maintain Muscle Mass While Losing Fat 

If you want to lose weight, you should lose excess fat tissue, not muscle mass. Studies have indicated that it’s important to focus on diet and exercise if you want to preserve your Skeletal Muscle Mass while losing weight

To do this, you need to make sure you’re losing weight “the healthy way:” 


There’s more to your body weight than what meets the eye—although having a healthy body composition can definitely help with that! Knowing how your fat and muscle contribute to your weight can give you key insights into your health and help you plan out a more specific diet and exercise routine for your goals. 


Erica Digap is a freelance writer specializing in nutrition science, fitness, and health. After receiving her BSc in Clinical Nutrition and working in the corporate diet industry, she decided to set forth and use her experience to inspire readers to make lasting, healthy lifestyle changes, one healthy meal and workout at a time.