The Fat Free Mass Index and approximating your bodyfat percentage-Updated 3/21/2016

The "natty limit" of a 25 Fat Free Mass Index (FFMI) is quite commonly known in those places on the Internet where all things lifting weights are discussed, debated, and argued.

Apparently it comes from a 1995 study where researchers compared pre-steroid era champion bodybuilders with a contemporary sample of "bros", some of which admitted to using steroids and others that claimed they had never used steroids.  Using the FFMI (a measure generated using maths that is beyond the scope of my meagre skillset), they determined that it was extremely unlikely that one could amass a FFMI of greater than 25 without the use of drugs.

That same study  also mentioned that the "natty limit" of 25 might not apply to "fat athletes" since there was an idea that there was some lean mass gained with excessive accumulation of non-lean tissue.  Whether or not that lean mass was muscle or just stuff that wasn't fat wasn't mentioned.  In any case, whatever this "not muscle but not fat" tissue might be, it apparently allows for a fudge factor (pun not intended but appropriate) in the FFMI "natty limit" for fat guys (like me).

Using the ever-abundant information available on the Internet, I decided that I could use FFMI and the "natty limit" to approximate my percentage of bodyfat.  This would prove to be a huge benefit for me since traveling to Toronto to have an appointment with a dual energy X-ray absorptiometry scan  (DEXA) would be both expensive and time consuming.

Because I have never used steroids or other drugs, I can comfortably assume the "natty limit" applies to me.  Because I'm also not built like a 1940's era bodybuilder, I can also assume that I am nowhere near the "natty limit" that correlates so strongly with champion bodybuilders of the pre-steroid era.





So, I picked a random site that had a FFMI calculator and plugged in some numbers.

First, I used my numbers when I was 21 yrs old and in my 3rd year at UCLA.  I was and still am 5' 9" tall but back in 1987, I weighed 178 lbs.  I had been weight training for about 7 years and had just started training to compete in powerlifting. Edit: At the time of the picture below, I had not recently attended the UCLA kinesielogy lab to test my bodyfat using the hydrostatic method.  I don't remember the exact reading but it was in the 9-10% range.  For purposes of this exercise, I'll call it 10%.  This was pretty much the only time in my life I've ever had my bodyfat % calculated using a reputable mechanical method.  Edit: I did later attend the UCLA kinisielogy lab and get my bodyfat tested but this picture does not reflect that condition.  In the picture below, I was lighter and leaner than when I attended the lab the next year.

178 lbs 5'9" approx 10% BF

Edit:  attached below is my result from getting my bodyfat tested two ways, hydrostatic and skinfold. I weighed 192 lbs and was given a result of 10% bodyfat.  Based on those numbers, my FFMI was over 25.  Believe me, I did not look like anything close to a champion bodybuilder.



Because I knew my height, weight, and bodyfat %, for this starting point, I'm just solving for FFMI. Plugging in the numbers, the FFMI calculator tells me my FFMI in 1987 was 23.6.  Lean mass of 161 lbs.  If you would've told me that I had already reached at least 94% of my likely genetic ceiling, I wouldn't have believed you.  If one does the same calculations using  15% bodyfat (because, let's face it, I wasn't super lean and the student running the test could've been distracted by my killer flat-top), the FFMI is 22.3 and the lean mass is 152 lbs.  Still doesn't leave much room to bump up against my "natty limits".

Fast forward to 2013 and 2014.  I don't take many progress or before/after pictures but every now and then, circumstances catch me without my shirt on as they did back in September 2013.  I later mimicked that picture to take a progress picture after losing some weight.  If I were Dan Bilzerian, I would've hopped on a private jet and recreated the picture at Ala Moana beach but I'm not so I was in my basement (like so many others writing about lifting on the internet--at least it wasn't my parent's basement).

Sept 2013, 255 lbs, Nov 2014 227 lbs
 This time, I'm solving for bodyfat %.  I know my height and weight but I'm using a FFMI of roughly 24.  Obviously I'm not genetically elite and I'm probably giving myself way too much credit by using 96% of the genetic maximum (for all intents and purposes) but I had to allow myself between 0.4 and 1.7 FFMI units progress over 27 years!

September 2013, 255 lbs, 5' 9"  FFMI 24.3  Calculated BF%:   35%  Lean mass 166 lbs
November 2014, 227 lbs, 5' 9"  FFMI 24.0  Calculated BF%:   28%  Lean mass 164 lbs

So, there you have it.  According to "natty limits", I'm approximately 28% bodyfat and have gained between 3-12 lbs of lean mass going from 178 lbs to 227 lbs.

If you search the internet for "body fat percentage pictures" there are a variety of sites but there are also quite a few different "looks" for each indicated bodyfat percentage.  In the end, it's all kind of ridiculous since one is either judged how one looks (bodybuilding) or how much one lifts (weightlifting/powerlifting).  Any actual measurement of bodyfat doesn't affect one's results in either.

The interesting thing is that 3-12 additional pounds of lean mass have contributed to almost 200 lbs on my powerlifting total* so at least I'm getting some bang out of it.


*yes, I have really only put about 200 lbs on my raw powerlifting total from when I started in 1987 to my most recent PR total.  Whether that's toiling in mediocrity or a labour of love is a question for another day.

EDIT:  Greg Nuckols recommended I try using the "US Navy Calculator" to estimate my bodyfat, saying it is reasonably reliable.  Using measurements taken near around when I was 227 lbs, the calculator spits out a bodyfat percentage of 21%.  Plugging that into the FFMI calculator gives 26.7.  Using measurements taken recently at 238 lbs, the US Navy Calculator also spits out 21% with a FFMI of 27.7.  So clearly the US Navy Calculator is broken according to the "natty or not" types that believe in "natty limits".   http://fitness.bizcalcs.com/Calculator.asp?Calc=Body-Fat-Navy

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