Since the beginning of my career I’ve emphasized the importance of paying attention to body composition over body weight alone. In most of my books I tend to base diet set up on body fat percentage as well as that determines a lot about someone’s physiology. But my numbers are generally based on older methods, primarily caliper measurement. And in that DEXA is becoming more common, I want to look at DEXA vs calipers for body composition measurement.
DEXA vs Calipers, etc.
One of the more recent approaches to measuring body composition is DEXA (Dual-Energy X-ray Absorbitometry) which does a full-body scan and can measure things like bone density (critical for women) and other tissues. And it gives what is proposed to be a more accurate estimate of BF% than older methods. It can even do something where it gives you one value for upper body and one for lower body. I suppose folks could use this to look at regional changes in BF% but I think whole body BF% is more valuable.
And here’s where it gets a little bit weird. DEXA seems to give systematically different measurements than other older methods. And it seems that they are usually higher. Case in point, a number of contest lean bodybuilders (who calipers or visual estimates might put around 4%, the lower limit for males) have been DEXA’d at like 9% or thereabouts.
And what I’m seeing online is that someone will ask for a visual estimate, they will be very lean and maybe estimated at 8% and someone will comment “Yeah, such and such contest lean bodybuilder was estimated at 9% so no way are you 8%, lol.” Lol indeed.
But here’s the thing, you can’t compare apples and oranges like this (well you can but why would you). DEXA gives different values than calipers gives slightly different values than other methods. Personally, I find it a little bit off that DEXA is putting someone who is at a BF% near death/their essential body fat levels (3-4% in men) at 9% but so be it. And clearly DEXA is measuring something else that is causing it to give these higher values. I truly have no idea what (maybe someone in the comments can comment by leaving a comment)
Consistency vs. Accuracy
But here’s the thing, you can’t compare apples and oranges like this. The old caliper/visual/etc. estimates are giving one value (and what most, including myself are using) and clearly DEXA is giving different (typically higher values). But they aren’t comparable.
In the series I linked to above, one point I make is that consistency is more important than accuracy. Make no mistake, it’s nice to have a semi-accurate estimate of BF% or whatever but it’s only an estimate. And even if two different methods are 5% different, it doesn’t make much of a difference in the big scheme in terms of estimating lean body mass (LBM) or calculating out diets. It’s just not that big of a deal.
More importantly, the differences don’t matter because it’s an estimate no matter how you cut it. More than that, being able to track relative changes is far more important than true accuracy. So say that calipers put you at 10% and DEXA puts you at 15%. Whatever.
And let’s say that you diet for a month and lose some amount of fat. Calipers say you’re 8% and DEXA says you’re 13%. Yes, the values are different but both dropped by 2%. They both picked up the relative change (that is they are consistent) even if they give different values.
DEXA versus Calipers Redux
More importantly, and this was a question that I got regarding some information on the site, all of my early books and articles use the earlier values via calipers or visual estimates. So in articles where I list some number, say 4% for a contest lean male or 10-12% for a contest lean female, that’s based on older methods. DEXA might put them around 9% and 16-18% respectively but I don’t care.
Or there is my diet Category system which divides men and women into one of three different categories based on their BF% (which determines a lot of underlying physiology). I use, 15% or whatever for Category 1 males. DEXA would say 19-21% or whatever. I’m using the older methods.
In the two books I’m working on, I will make the above more clear and provide values for both. But again, to chortle “You’re not 8% b/c DEXA says some contest lean guy is 9%, lol” is missing the point. The 8% is via the older methods, and the 9% is by a newer different method.
As my favorite author once wrote
“A man with one watch always knows what time it is, a man with two is never sure.”
Ponder on this until you understand and you might earn entrance into the Illuminatty.