### Lean body mass or lean body weight: A waste of arithmetic?

Sometimes, people ask me to explain what is **lean body mass** or lean body weight. However, it is not what you think. Indeed, lean body mass has nothing to do with your ideal weight or what your body should be like if you were ‘lean’.

Lean body mass refers to the sum of the weight of your bones, muscles and organs. Basically, lean body mass is the sum of everything other than fat in your body.

However, who would like to have a body with ZERO fat? Nobody. In fact, you’d probably die if you had no fat.

So why is it included along with the Body Mass Index (BMI) on the body surface area calculator page? Because it’s kind of **fun **to think about. That is all.

In addition, some medical formulas use lean body mass for calculations of organ function and medication doses.

Maybe you are wondering why your lean body mass goes up as your weight increases even though your height is unchanged.

The reason is because skeletal muscle mass tends to increase as body fat increases. It takes extra muscle to carry extra fat around, right?

Hope this helps!

### The Formula for Lean Body Mass

The formula for lean body weight using the method of James^{1,2} is:

Lean Body Weight (men) = (1.10 x Weight(kg)) – 128 x ( Weight

^{2}/(100 x Height(m))^{2})

Lean Body Weight (women) = (1.07 x Weight(kg)) – 148 x ( Weight^{2}/(100 x Height(m))^{2})

An alternate formula for lean body mass using the method of Hume^{3} is:-

For men over the age of 16: lean body mass in kilograms = (0.32810 * (body weight in kilograms)) + (0.33929 * (height in centimeters)) – 29.5336

For women over the age of 30: lean body mass in kilograms = (0.29569 * (body weight in kilograms)) + (0.41813 * (height in centimeters)) – 43.2933

These formulas are trusted and highly scientific and are based on various types of measurements of human body composition. The measurements include dual energy X-ray absorptiometry (DEXA). However, remember that they are based on ‘averages’. The measurements predict the lean body weight ‘average’ of a group of people with similar height and weight.

However, an individual might have more muscle than others in your average group. Furthermore an individual may have bigger internal organs or denser bones. Indeed, there are any number of factors that make one individual a little different than others. Thus, even the lean body weight formulas are estimates.

### References

- Hallynck TH Soep HH et al. Should clearance be normalised to body surface or to lean body mass? Br J Clin Pharmacol. 1981; 11: 523-526.
- James WPT. Research on obesity. London. Her Majesty’s Stationery Office.
- Hume R. Prediction of lean body mass from height and weight. J Clin Path. 1966; 19

- Mettler S, Mitchell N, Increased protein intake reduces lean body mass during weight loss in athletes. Med Sci Sports Exerc, 2010; 42:326-37.
- Volek JS, Volk BM, et al. Whey protein supplementation during resistance training augments lean body mass. J Am Coll Nutr. 2013; 32:122-35.