Fat vs Muscle Density – What’s the difference?

Fat vs Muscle. I bet you’ve heard the saying muscle weighs more than fat, but is it true? Is one more dense than the other? Does it affect how you’ll look?

The Science

Weight is weight. The difference is the density. That’s why two things that weigh the same can look hugely different in size. A 1kg pile of feathers would look much bigger than a 1kg pile of rocks. Muscle is more dense than fat and so 1kg of fat will look much larger than 1kg of muscle. In fact the picture below shows exactly what 1kg of each looks like.
Kg of fat vs kg of muscleAs you can see, the volume, or size, of 1kg of fat will take up much more space thank 1kg of muscle in your body, so of course you will look larger or ‘fatter’ with more fat than muscle. This is why you mustn’t become too obsessed with just losing weight. Fat is an essential part of our body and we need some but too much is not healthy. Fat helps to insulate the body and keep you warm. Muscle boosts metabolism, it needs more energy to keep it going. So, having more muscle means you burn off more calories while resting.

Don’t be obsessed with your weight

If you see a friend walking down the street, you don’t pick them up and say ‘ooh you’ve lost weight’ you notice what they look like and take in their shape. In fact, that friend may not have lost any weight at all. They may simply have started to lose body fat and gain muscle mass (otherwise know as toning) Weight should not be the only factor to being healthy. 

In this picture, the women are all the same weight but all look different. (154lbs or 70kg) Weight isn’t everything. Body fat percentage is much more important.

Or how this fitness trainer’s weight and body changes. (Kelsey Wells)

Weight Change


Don’t get disheartened if you’re exercising and not losing weight

For some people starting out, just doing some light exercise and losing a few pounds is great and the best start. However as you progress, at some stage you will plateau. Don’t worry. Look at the big picture. Step back and look at yourself in the mirror. Maybe you see changes to your shape. Maybe you’re building muscle underneath some excess fat. It’s a slow process and will take weeks or months for you or other people to notice. Measure yourself, waist size is always the best place to start and record it. Record other areas as well to see where the fat starts to come off first. Depending on where you’re starting from or your body type, not losing weight shouldn’t necessarily be seen as a bad thing and total body weight is not always a true indicator of what someone looks like or how healthy they are.


You can’t chose where you’re body stores fat and neither can you chose where your body loses it from. However, you can decide which muscles you want to develop.

Lose fat not weight, that should be the saying.

(If you want to see what body fat % you should be for your age or gender the How Does The Body Store Fat – Men & Women page will give you a good idea)


BMI – It’s flawed

Body Mass Index, or BMI, is often mentioned as an indicator of how healthy or over/under weight someone is and while it is not a bad generic tool, it is flawed. According to health institutions, the higher your BMI the higher your risk of diseases like type 2 diabetes, heart disease and high blood pressure as well as others.

It measures your weight in kg’s divided by the square of your height in metres. It does not differentiate between muscle and fat. Nor does it take into account gender, age, body types or fat distribution.

In Why Should Older Adults Exercise it explains how our muscle mass decreases as we age and we naturally store more fat. So, in theory, an elderly person with low muscle mass and higher body fat percentage could have a low BMI. This will imply less risk of diseases, and a fit, strong, athletic person can have a high BMI implying they are overweight or even obese and therefore at higher risk of these diseases.

You can generally look at someone and see if they are over or underweight. Even though BMI does have its limitations it is not bad for most people to get a starting point for their health, as long as it is used in conjunction with some other form of test or a doctors visit. It should not be used solely as an indicator of someone’s health and this is why some doctors are shying away from it. A better form of test is the waist to neck ratio.



  1. Improving your fitness shouldn’t just be about a number on the scale, so I would advise that you do your best to focus on how you feel, what you can achieve and how beneficial it is for overall wellness. My question is how is it possible to shift ones focus from weight loss to fat loss?

    • Hi and thanks for your comments, I completely agree with you on making sure you feel comfortable in yourself. There is no point in making yourself feel exhausted all the time or generally unwell just trying to lose that extra couple percent body fat or lose a few more pounds. A certain level of fitness will improve your daily tasks and give you more energy to do them but taking it too far can also have detrimental effects. Coming to your question about shifting your focus from weight loss to fat loss, it is just trying to think about your body differently. What are my goals and what can I do to start achieving them. If you can take a step back and forget about your weight to begin with and focus on what do I need to do to reduce any excess body fat. Whether it’s a change in diet, starting or changing your exercise routine. Remember if you only diet without exercise you will only become a slimmer version of your current self. If you build up some muscle strength as well that will shape the body more but more importantly it will burn more calories while you rest. Good luck

  2. As someone who is overweight, I enjoyed reading this post.  It’s easy to just focus on the number on the scale (which is what I tend to do).  Your information on fat vs muscle mass is interesting and one I don’t tend to consider.  When my weight plateaus, I tend to give up but your pictures of the different body shapes on women who are all the same weight are eye-opening.  And I like your suggestion to take measurements as a better judge of where I am in my journey.  Thank you for posting!

    • Hi Cynthia, thank you for your comments, I’m glad you enjoyed it and that I could bring something extra. You’re right in that it is difficult to get away from weight being just a number. Your weight is important but it must be taken in context with everything else. I wish you luck

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