Disclaimer: Power Athlete HQ, Power Athlete Nutrition, and myself are not medical professionals. If you or someone you know may be displaying behavior associated with disordered eating, please seek proper medical assistance.

Previously I highlighted the current data that shows we, as a population, are too fat and the dangers associated with that. While I attempted to present an unbiased format, I would be remiss to not cover the other side of the coin. Being too lean is no more healthy for you than being morbidly obese. Though the outcomes may look different, they will both have severely negative effects on your overall health.

What is “Too Lean”?

Being “too lean” would mean that one’s low level of body body fat is starting to negatively impact their health and/or performance. When talking about athletes, some sports are at higher risk of this. Specifically endurance athletes, gymnasts, divers, combat athletes, and figure athletes or body builders. This is because their sports rely on either aesthetics, weight class qualification, or a sustained power output which can be increased by literally “trimming the fat” from the load they are moving. Competitive cyclists, for example, will go to great lengths to drop fractions of kilograms because, over the course of a race, that adds up to a significant amount of work saved. So while there is a definite performance advantage, how can we accurately assess this to help our athletes stay lean and healthy.

Measuring Body Composition

To objectively put numbers on being “too lean” we can either look at blood tests where there may be hormonal disturbances or severe deficiencies in our fat soluble vitamins despite adequate intake. Specific to women we may see secondary measures in an amenorrheic state (1). A less invasive, and more readily available method, would be to measure an estimated body composition via one of several techniques. When measured accurately, the threshold set for an unsustainable level of body composition is typically put at ≤5% or 15% for men and women, respectively. These are numbers that can be reached for a short period of time, such as competition day for physique and bodybuilding athletes, but should not be maintained for much longer than that. With that in mind, let’s see how one can measure their body composition.

The Gold Standard

The only 100%, well…99.99%, accurate measure of body composition is impossible to do for those who want to live. If you’ve seen the music video for Pink Floyd’s “Another Brick in the Wall pt. 2”, you have an idea of what needs to be done. While you don’t need to necessarily grind up bodies, you do need to dissect the tissues from one another. This means separating the fat mass from the fat-free mass (bone, muscle, organs, etc.). We call this the “Two Compartment Model”. You can see why this would be an issue, right? It has been done but, unfortunately, many of the studies were before the 1900s and had glaring issues that render the conclusions invalid. Thankfully there was one more recent study published in 1984, using 25 Belgians who died of natural causes(2, 3).  And, even then, the conclusion was that individual variance was so high that modern in vivo methods of measurement are not accurate. Read that again, no method of measurement is truly accurate. Don’t @ me on this, just accept it. Now, with that pill swallowed, let’s move on to more common and attainable forms of measurement.

A Fool’s Gold Standard

Since we can’t slice and dice our clients, we need to get close enough. The best way to do this is not a DEXA scan, despite common belief. It is in a hydrostatic weighing tank. This is a form of densitometry, the measuring of a body’s density. We know that fat-free mass is denser than water but fat mass is not…fat floats. The degree to which it floats relies on the temperature of the water, but that can easily be controlled. But what else floats in the human body? If you guessed the giant balloons we call lungs, you might have a career in science. And the truth is we can’t fully exhale our lungs, so we estimate the residual volume, or air left in the lungs after a full exhalation. And it’s that estimation that adds, under the best circumstances, a 2% error in the measurement. So now our 6% man or 16% woman might read as low as 4% and 14% or as high as 8% and 18%. But that’s assuming you are comfortable sitting under water for ~10-15 seconds with no air in your lungs and are able to hold as still as possible. Having ran this test on hundreds of people, it never goes that smoothly (4). So let’s find something that is a little more…comfortable.

The People’s Choice

The DEXA (Dual Energy X-Ray Absorptiometry) Scan. Often touted as the gold standard, but the method is full of error that often goes unmentioned. While it does add some value by splitting things into a four component model (water, mineral, protein, and fat), it does not accurately account for some very important measurements. First, this method was initially designed specifically for measuring bone mineral density, not total body composition (5). In trying to apply this method to measure fatness, there are assumptions requiring correction factors to be applied that have been shown to be less accurate for subjects outside of specific age ranges (6). The machine also shows a bias towards those with a thicker tissue to penetrate, meaning there will be a bias for those who have more fat or muscle (7). There is an issue of assessing individual pixel difference, which all the scan is doing, so when there is fat on top of a bone it will make assumptions based on surrounding pixels (8). Depending on the instrumentation used, it may completely disregard the soft tissue of the head in it’s assessment (9). And most importantly, the prediction equations the DEXA scan uses are based off of the equations developed using hydrostatic weighing, thus starting the entire process off with inherent error. Because of the several potential sources of error, some dependent on the manufacturer, it’s difficult to say specifically what amount of error would be in your measurement.

The Shocker

The previous two methods are lab based measures meaning you won’t have access to them easily. But one very accessible method is bioelectrical impedance analysis (BIA). This is commonly used as an InBody unit, but this method is also popular in many of the at-home scales with metal plates that you stand on. This method measures the length (L) and resistance of a conductor (R) to determine a volume (L²/R). In layman’s terms, it sends a small electrical current through your body. So, in reality, this measurement relies more on your body water rather than body fat. There are two major assumptions causing error In this method (10). First, the equation assumes you are measuring a cylinder. While your body is round, it’s not a perfect cylinder. Second, it relies heavily on hydration status being constant. This can be controlled for in the lab by analyzing urine density, but that’s not a common thing happening in your home or gym. And, for the measure to be as accurate as possible, there should be four sensors, such as the InBody, so the current has a more direct route (a contralateral foot-to-hand measure). At-home scales send a current from one foot to the other, taking longer to measure and allowing for a greater loss in signal strength. These errors combined with, once again, the use of hydrostatic weighing estimates as reference values, mean BIA will, in laboratory conditions, add another 4% of error to the already present 2% error. In the uncontrolled setting of the gym or home, it’s more variable. Your 6% or 16% may read as low as 0% or 10%. Zero percent! But you might also see a 12% or 22%. 

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In A Pinch

Our last common method is one of the oldest indirect methods used, body calipers. Since these devices are so rudimentary, they are often looked down on in a technological bias. A DEXA is a big fancy machine, so it must be more accurate than these little pinchers, right? Hold onto your butts. With a skilled practitioner, this method may result in as little as 3-5% error (12). Still gravely unacceptable in terms of accuracy, but no more inaccurate than the other common methods. There are three major sources of error with this method. First, is user error. The inter-tester error, meaning difference found when two different people test you, will vary. Depending on how many times they’ve made these measurements and the device used (yes, not all pinchers are created equal) you may find quite the different result without any actual change. Next to inter-tester error is the amount and locations of sites measured. Men and women deposit fat stores at different locations, so different sites are used in the prediction equations. And several of these equations will produce vastly different results even with the same tester (13). Now, the obvious issue is that this method selects arbitrary spots to measure. If you look at the literature, there are several studies trying to decide which areas are most important. Some even measured skin thickness in the finger. Lastly, and tell me if you’ve heard this one before, they are using the equations from the hydrostatic weighing estimates as reference values. So while you might only get 5% error with a highly-trained individual, you can get up to 7% or more with these measures. 

A Futile Effort

So there it is, measuring body fat is a waste of your time. Not only because the methods available are riddled with error, but because the likelihood of you needing to be concerned about being too lean is not real. I want to reiterate that I am not saying disordered eating or body composition issues aren’t real. As someone who spent over a decade coaching elite swimmers and endurance athletes, I am very aware of this reality. What I am saying is that for the general population, it’s a non-issue. I presented the data in my last article, we are without a doubt too fat. So, according to the data, you just need to lose body fat. You don’t need to know how much you started with to do that. If you’re looking for a measure: see how your pants fit. If they’re getting looser in the waist you’re probably trending in the right direction. If you want another measure, take your shirt off and look at your stomach. Do you have “capped delts” or a visible differentiation between your obliques and abs? If yes, you’re somewhere sub 15% or 25% (men and women, respectively). If no, you’re closer to 20% and 30% (men and women, respectively). And just to remind you from what the data showed in the last article, being that high or higher will negatively affect literally every component of your life and your training. Injury recovery, ability to put on muscle, sleep, mental health, sex life…you name it, it will be negatively effected. 

What to do about it

If you are an elite athlete or coach of an elite athlete who would see a performance gain from accurate assessment of body composition (read: gets their paycheck from their sport), call your nearest university. The number might not be as accurate as possible, but it will be more accurate in the lab than anywhere else. If they can’t assist you they will likely know what direction to point you. If you’re a normie, whether you’re looking to dip below that 10% mark or just trying to get healthy, you need a coach because either way there is a need for a lot of accountability. Being sub-10% or 20% means you will be hungry more often than not so you’ll need a voice reminding you of why you’re doing this. You can sustain a healthy life below 10% and 20%, it’s just not easy. If you’re above the 20% or 30%, you need a voice reminding you that it’s alright to be hungry. I see the amazing things Dr. Matt Zanis (@rootedinmvmnt) is doing with clients who are injured and applaud him. But I watch his instagram posts and see a recurring theme: everyone is carrying extra fat. If you’re injured, you won’t think twice about the need for a movement coach. Why are you lying to yourself about the need for a nutrition coach? 

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1. Bale P, Doust J, Dawson D. Gymnasts, distance runners, anorexics body composition and menstrual status. The Journal of Sports Medicine and Physical Fitness. 1996 Mar;36(1):49-53.
2. Clarys, J. P., Martin, A. T., & Drinkwater, D. T. (1984). Gross tissue weights in the human body by cadaver dissection. Human biology, 459-473.
3. Clarys, J. P., Martin, A. D., Marfell‐Jones, M. J., Janssens, V., Caboor, D., & Drinkwater, D. T. (1999). Human body composition: A review of adult dissection data. American Journal of Human Biology: The Official Journal of the Human Biology Association, 11(2), 167-174.
4. Bonge, D., & Donnelly, J. E. (1989). Trials to criteria for hydrostatic weighing at residual volume. Research quarterly for exercise and sport, 60(2), 176-179.
5. Wells, J. C. K., & Fewtrell, M. S. (2006). Measuring body composition. Archives of disease in childhood, 91(7), 612-617.
6. Koo, W. W., Hammami, M., Shypailo, R. J., & Ellis, K. J. (2004). Bone and body composition measurements of small subjects: discrepancies from software for fan-beam dual energy X-ray absorptiometry. Journal of the American College of Nutrition, 23(6), 647-650.
7. Mitchell, A. D., Scholz, A. M., & Pursel, V. G. (2000). Dual‐Energy X‐ray Absorptiometry Measurements of the Body Composition of Pigs of 90‐to 130‐Kilograms Body Weight. Annals of the New York Academy of Sciences, 904(1), 85-93.
8. Laskey, M. A. (1996). Dual-energy X-ray absorptiometry and body composition. Nutrition, 12(1), 45-51.
9. Williams, J. E., Wells, J. C., Wilson, C. M., Haroun, D., Lucas, A., & Fewtrell, M. S. (2006). Evaluation of Lunar Prodigy dual-energy X-ray absorptiometry for assessing body composition in healthy persons and patients by comparison with the criterion 4-component model. The American journal of clinical nutrition, 83(5), 1047-1054.
10. Chumlea, W. C., & Sun, S. S. (2005). Bioelectrical impedance analysis. Human body composition, 2, 79-88.
11. Ackland, T. R., Lohman, T. G., Sundgot-Borgen, J., Maughan, R. J., Meyer, N. L., Stewart, A. D., & Müller, W. (2012). Current status of body composition assessment in sport. Sports Medicine, 42(3), 227-249.
12. Durnin, J. V., & Womersley, J. V. G. A. (1974). Body fat assessed from total body density and its estimation from skinfold thickness: measurements on 481 men and women aged from 16 to 72 years. British journal of nutrition, 32(1), 77-97.
13. Sinning, W. E., Dolny, D. G., Little, K. D., Cunningham, L. N., Racaniello, A. N. N. E. T. T. E., Siconolfi, S. F., & Sholes, J. L. (1985). Validity of” generalized” equations for body composition analysis in male athletes. Medicine and Science in Sports and Exercise, 17(1), 124-130.

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