You Shouldn’t Care About Your Bodyfat Percentage
Takeaway Points:
Body composition is a popular metric for measuring overall fitness and physique, but it has significant drawbacks to its use.
There are no publicly available and reliable methods for measuring body composition, which means that the metric itself is less useful (and often more discouraging) than it should be.
While it may “seem” less scientific or data-focused, in reality, ditching or de-emphasizing body composition in favor of other methods can generally produce better results.
For a long time, we had relatively primitive methods for assessing the physical health of an individual. After all, it’s hard to look at someone, and just immediately know whether they’re generally “healthy” or not.
I’ve written before about how “healthy” is usually a bad way of thinking about it. Most people assume that skinny people are healthy, but everyone has different risk profiles for different health issues, most of which aren’t visible. I’ve been through years where I was skinny but a smoker, or years where I was generally looking good lifting heavy all the time but never did any cardio and never paid attention to my diet, and my blood pressure suffered as a result. Fatphobia attempts to reduce it to “fat or not” when fatness, on its own, isn’t really a good reliable assessment for someone’s habits and risk factors.
For a while, body mass index (BMI) was a regularly used metric. BMI is a pretty simple ratio of your weight to your height - meaning that, your height staying (mostly) the same, it’s basically just another proxy for your weight, and assesses whether you are “under” or “over” weight based essentially just on your bodyweight.
Then we had the rise of body composition, also known as bodyfat percentage. If your bodyfat percentage is 20%, for example, this means that fat makes up about 20% of your bodyweight, and the remaining 80% is muscle, organs, bones, etc. With most of that stuff (organs, bones, etc.) remaining mostly stable in weight, this means that this is a pretty good proxy for your overall leanness, and your overall fitness. A person could be “overweight” by BMI, but very muscular and lean, and thus unlikely to be unhealthy.
Likewise, we have the concept of “skinny fat” people (people who are relatively light, but have low muscle tone and still have a decently high bodyfat percentage) to refer to skinny people who may still be somewhat unhealthy despite their light weight.
The rise of body composition as a metric has been such a success, that it’s often the only thing most people care about. I can’t tell you how many people come to me for coaching with some variant of the line “I don’t care about the number on the scale, I just want to get leaner”.
There are numerous methods for testing body composition, some of the most common of which are these:
Bioelectrical Impedance - This method involves touching two electrodes which are used to send a weak electrical current through the body. Given that electricity travels more slowly through fat than other tissues, it uses the time it takes for the current to complete its circuit to estimate how much bodyfat you have.
Skinfold Calipers - This method involves measuring folds of skin at various points on your body. The thicker the folds, the more bodyfat you’re holding, so this can be used to estimate how much bodyfat you have.
Navy Calculator - By getting various measurements (waist, neck, height, etc.), you can estimate body composition.
Hydrostatic Weighing - Given that fat is less dense than muscle by weight, the amount of water you displace can be used to estimate body composition.
Bod-Pod - Air pressure within a confined chamber is used to determine the density of your body, and similarly to hydrostatic weighing, this can be used to estimate body composition.
Ultrasound/DEXA - Your body is subjected to ultrasound/X-rays, and this is used to estimate body composition.
3d Scanners - You step in a giant scanner which basically gets a big model of your body and uses this to estimate your body composition.
Apps/AI - Wildly enough, there are now apps that can ostensibly estimate your body composition from a photo alone!
Note that I say “estimate” body composition in all of these methods, and this is for a very important reason - none of them are necessarily very accurate.
The terrifying reality, is that there are no highly reliable and accurate methods for measuring body composition.
Some of them are certainly more accurate than others. Bio-electrical impedance is commonly used because it can easily be integrated into cheap hand held testers or body weight scales, but it is also notoriously unreliable. DEXA is considered the most accurate, but it requires that you use expensive, specialized equipment that will cost you quite a bit of money to use, and even then it has huge potential for error.
The reason for this is pretty simple - body composition is never really being actually measured, because doing that would essentially mean checking every cell in your body to see if it’s fat tissue or not. The only real way to do this, is to essentially chop up the limb and analyze it with a microscope post-mortem, so it’s not generally possible to do real body composition tests on human beings, since we don’t want to actually die or lose limbs just to check how much muscle mass we had at a given time.
So instead, when you’re using any of the above methods, they’re just estimating your body composition by testing proxies for leanness, and then comparing you up against more or less lean people.
The end result is that every body composition testing method has SOME way that it can be made less accurate, because human bodies are just different, and minor variations between you and the next person can mean big differences in body composition tests. The folks at MacroFactor have a great writeup on the research here, if you’re interested in reading a lot more about it. Similar to how you can mess with things like breathalyzer tests, drug tests, or polygraph tests to get false results, you can mess with body composition tests in the same way.
As a result, even the most accurate body composition tests can have much larger margins for error than people expect, and may not be of any practical benefit.
So what can we do instead?
The problem here is that the fundamental IDEA of measuring your body composition (that you want to have a higher relative amount of lean mass, and less of fat mass) is solid. Generally, if you’re getting very lean, this is very beneficial for physique and performance related outcomes.
The problem is that we like to have very precise numbers which give us a very clear sense of our progress, and the reality is that those numbers really don’t exist, or don’t line up to our lived realities. It would be nice if we could reliably measure, say, 8% bodyfat and assess accordingly, but the reality is that any test that tells you that you’re 8% bodyfat could easily have errors of ±5% on top of that, rendering that 8% value kind of useless.
At the end of the day, there are plenty of rough proxies that you can use for leanness, like waist measurements, weight on the scale, and so on - all other factors being equal, then losing weight, or your waist measurement decreasing, are pretty good proxies for you getting leaner. But, in general, folks want to put precise numbers on it, which is where things can get messy.
For example, I know folks who go through entire bodybuilding cycles, gain a significant amount of muscle mass, retain more of it on their next cut, but then they get a single bad body composition test which implies that their body composition has worsened, and this makes them think that they’ve wasted a year of training.
At the end of the day, while it’s very unscientific, the reality is that often, looking in the mirror, and comparing progress photos over time, is really the best thing you can do. You can focus on leaning out until you’re happy with your current level of leanness, then pull back. You don’t need to be obsessed with hitting any particular bodyfat percentage, because all the numbers are somewhat inaccurate anyway.
I still use body composition measurements in my own training, and with my clients. However, I only use this as a VERY rough yardstick for progress - if waist measurements or estimated bodyfat percentage are decreasing over time, then this is generally a good sign that you’re getting leaner, and you don’t need to worry about specific numbers or hitting specific number targets. Instead, rely on other factors - how you look, how your clothes fit - as better senses of what this body composition change means to you.
About Adam Fisher
Adam is an experienced fitness coach and blogger who's been blogging and coaching since 2012, and lifting since 2006. He's written for numerous major health publications, including Personal Trainer Development Center, T-Nation, Bodybuilding.com, Fitocracy, and Juggernaut Training Systems.
During that time he has coached thousands of individuals of all levels of fitness, including competitive powerlifters and older exercisers regaining the strength to walk up a flight of stairs. His own training revolves around bodybuilding and powerlifting, in which he’s competed.
Adam writes about fitness, health, science, philosophy, personal finance, self-improvement, productivity, the good life, and everything else that interests him. When he's not writing or lifting, he's usually hanging out with his cats or feeding his video game addiction.
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