Why what you thought about lean body mass is wrong.

Why what you thought about lean body mass is wrong.

When we talk about weight loss, we are focusing on fat loss. For instance, if the scale weight stays the same, but lean body mass has gone up and fat goes down that is seen as a success.

This is true. But people assume it is just muscle. But that’s not 100% true. 

Lean body mass constitutes all of your body weight, which is not body fat.

This includes:

  • Muscle
  • Water 
  • Bones
  • Organs
  • Skin
  • Food matter

This means if you carry a lot of water, this would increase your lean mass.

How is lean body mass calculated?

To calculate your lean mass, you’d subtract your body fat mass from your total body weight.

This can be done in various ways.

You can get a skin calliper reading to estimate your body fat percentage, from there you can subtract that from your total body weight.

A DEXA scan will give you a somewhat accurate reading of your body fat percentage.

Or you can do what I do and use a set of scales, which will estimate your body fat and lean mass. A word of note. Any set of scales you buy will never be 100% accurate. But they are usually consistently wrong. What this means is; if you are losing body fat, the body fat readings will decrease. And if you gaining lean mass then the lean mass readings will increase.

However, I will say again. As great as it is, to know what your numbers are, they are not the be-all and end-all. It’s good to have an idea, but obsessing over them meticulously would be a waste of time.

What is a healthy percentage?

What is healthy will depend on whether you’re male or female. Men will on average have a higher lean mass. This is because women tend to carry more body fat, thus their lean body mass readings will be lower.

These are what have deemed the sweet spots depending on gender:

Male: 80-88%

Female: 70-80%


If the lean mass is too low, it would be assumed that body fat percentage, must be high. When body fat percentage is too high, that can lead to various health risks such as:

  • High blood pressure
  • High cholesterol
  • Type 2 diabetes
  • Joint issues and mobility
  • Various cancers

On the other end of the spectrum if the lean mass is too high. This would be assumed body fat percentage is too low, this can also lead to health risks. These risks include issues such as:

  • Weakened immune system
  • Malnutrition
  • Fertility issues


Lean mass vs BMI

There’s a lot of debate about whether BMI is a good indicator of health. There are a lot of people who claim BMI is a load of rubbish and should be totally dismissed. 

That’s an extremist way of seeing things. BMI is not amazingly accurate for an individual person. However, when undertaking whole populations BMI does have its place.

For instance, the ‘normal’ BMI range is 18.5-24.9. Over that you’re overweight and under, you’re underweight.

For most people this is a quick and OK basis, to work from. For instance, if you have a BMI of 32 or 14, that is probably an indicator, that you are increasing certain health risks.

However, if you have a healthy lean mass range, but your BMI is 1-3 over, you’re most likely still healthy. BMI does not take into account muscle weight for instance. So if you regularly lift weights and eat a high protein diet and have a low body fat percentage, you most likely don’t have any issues.

The reason I have an issue with people saying BMI is useless is that they bastardise the idea of muscle causing a high BMI. Usually, someone will say a certain actor has an “obese” BMI and is very lean therefore, BMI is useless. What they don’t realise, the said actor takes copious amounts of steroids, therefore their reading is totally nullified.

Unless you’re taking steroids, you’re never going to have a BMI of over 30, just from muscle and lean body mass. 

How to improve lean mass

There are 2 ways to improve your lean body mass.

  • Lose fat
  • Build muscle

Despite fat and muscle being only 2 elements of your lean mass. These are the only 2 elements which we have control over.

Losing fat requires a caloric deficit. Losing fat for most people is the most effective. Most people carry more body fat than what is recommended, so losing some makes a great difference.

Building muscle requires progressive overload in the gym, adequate-protein windows and enough calories to fuel training. 

Overall, these are the 2 ways you can increase your lean mass.

Final thoughts

Whilst most people believe lean body mass to be muscle. This is not the case. It’s easier to see it like your whole body weight, minus your body fat.

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