Let’s let the Moose explain this one.

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

Whoever wrote that headline, likes bluntness.

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’.

Do people actually ask you questions like that?

Not for a long time. Actually, I can’t remember the last time.

Praise be to Wikipedia and Google.

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.

There’s a nursery rhyme about Jack Sprat, could eat no fat… The modern version: Jack and his wife try a bunch of diets and write a blog.

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.

Building a play fort in the kitchen is also fun.

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.

No. I wasn’t wondering that. But I was wondering whether to go and get a cupcake or a donut.

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 ( Weight²/(100 x Height(m))²)
Lean Body Weight (women) = (1.07 x Weight(kg)) – 148 x ( Weight²/(100 x Height(m))²)

An alternate formula for lean body mass using the method of Hume³ 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

Dammit. Two formulas. My OCD makes me wonder which is better and are they in the correct order?

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.

Oh, I think that I have a bigger organ than the average in my group.

Oh Hector. You always have to lower the tone. I think that the doctor is talking about internal organs.

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

The above references were from the original page in 1999. I’ve updated in 2014 and found a few more references below.

Also, there’s a Lean body mass calculator on the body surface area page.

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.