Yesterday I challenged you to estimate my body fat percentage by looking at a recent picture. To be scientific about this little exercise I chose to reference as the correct answer the results of the “gold standard” hydrostatic weighing I had subjected myself to at the Malibu gym (it was actually a specialized truck that shows up once a year and performs the intricate and expensive underwater weighing tests for $60 each). 317 of you took a stab at guessing from the photo of me. It’s clear to me that many of you are quite good at estimating actual body fat levels (the average guess was 6.7%), but Gwen, anticipating the tenor of today’s post, took the prize with the closest guess at 12.5%… Ironically, that was also the highest guess of all and yet it was still a full 4 percentage points lower than what the actual “gold standard” test demonstrated. That’s right, my test score showed that I am 16.9% body fat. That’s 28 pounds of pure fat – if you believe the lab values. Even my wife Carrie tested lower at 13%. Am I really that fat? Probably not, but I went through this exercise to illustrate a point about which I will write today: that quite often, these so-called “gold standard” lab values are of little actual predictive value. Sometimes these tests are just plain wrong. And sometimes they can create far more problems than they solve. And if they are that far off when something is largely visible, what happens when they are dealing with more intricate hidden body chemistry? In this case, my jeans still fit loosely, so I really don’t care what the lab value was. I know the reality. But if I lived only by the lab values, I’d be inclined to start cutting calories immediately to lose weight.
In my estimation, medicine has become way too reliant on testing for lab values that reflect aggregates, population norms, cohort quintiles from dubious studies, or simple averages to arrive at reference ranges and the calculated risk factors that these numbers appear to represent. Even the term “risk” is deceptive, because an increase in risk for a disease doesn’t guarantee you’ll actually get the disease – even if you show a strong genetic predisposition (another test I wonder about). Sometimes the preventive or prophylactic treatments that follow such tests are useless or even harmful. Nevertheless, doctors often prescribe, biopsy, radiate, excise or otherwise operate based on assumptions they have made regarding your relative risk of disease – and sometimes simply on their relative risk of getting sued if they don’t follow the standard of care – based solely on lab values. We have spoken here often about how medicine is not “black and white” and how there is typically not a right answer to a medical issue so much as an educated opinion (or not) on a course of action. It’s my contention that your own opinion is often the most precise and valid. Certainly, use your doctor, but do your own research to be sure you make an informed decision.
Case in point, I had breakfast with a friend a few weeks ago who wanted my opinion on his recent blood tests and whether or not he should continue taking statins. Right off the bat I told him (as I am telling you now) that I am not an MD and am not allowed to advise anyone on any medical issues whatsoever. So we agreed to have a philosophical discussion (like we are having here now). He showed me the results of two blood lipid panels taken from the same sample (blood drawn in the same collection sitting) but that were sent to two different labs that same day. Of course, as I anticipated, no two lab values were the same from one lab’s test results to the other. Most notably, the total LDL differed by 40% from one test to the other. That’s a little disconcerting in itself. On both of these tests my friend’s total cholesterol was way under 200 and his HDL was over 100, which “philosophically” would put him in the lowest risk category for CHD regardless of which test was the more accurate. But my friend has been running scared his entire life because his father had a fatal heart attack at age 51. As a consequence, he has it in his mind that he needs to get the lowest LDL score he can possibly muster, come hell or high water and regardless of the notion that very low cholesterol levels are associated with an increased risk in overall mortality. He eats well (mostly Primal) and gets a lot of exercise on his road bike (in my opinion maybe too much) but he still lives his life in fear of what the numbers might represent. And he agonizes over which data set is the “real” one. At his doctors urging he has even been taking statins as a “precautionary and preventive” measure (and now complains of fuzzy thinking). We ended the conversation with my telling him, ironically, that his relative risk of death or disability from riding his bike 200 miles a week on those mean streets in an effort to protect his heart is measurably higher than his risk of having a fatal MI that might result from his pure cholesterol numbers. And his increased risk from the stress of worrying probably trumps them both.
I have mentioned my skepticism of lab tests in the past (Makes My Blood Boil, Weighing the Evidence: Science and Anecdote in Nutrition Studies). It started when, as anti-doping commissioner for the International Triathlon Union I was obliged to prosecute athletes for doping violations when their tests showed 4 or 5 billionths of a gram of a steroid metabolite at a time when the legal allowable threshold was “only” 3. A billionth of a gram could then be the difference between being labeled for life as a cheater or competing legally. Seeing how imprecise lab tests can be from one lab or one machine to the other, and how these wavy lines on sheets of graph paper could be interpreted so differently from one “expert” to the next, my skepticism grew. At some future date I will get into details regarding the many common diagnostic tests that are now being re-evaluated for their lack of effectiveness (mammograms, colonoscopies, CT scans, etc) but for now, if you want a really scary example of how nebulous lab values can influence serious medical decisions, go here and read what the National Cancer Institute has to say about using PSA values to diagnose prostate cancer and read the answer to question 4. Turns out the gold standard for diagnosing prostate cancer relies on a test for which it is acknowledged there is no “normal” or “abnormal” PSA. And that while the “over/under” lab value for a biopsy has historically been set at 4.0, 65-75% of men who have PSAs of 4.1-9.9 are found NOT to have prostate cancer. More damage is often done by the subsequent invasive test (biopsy) than by leaving things as is. Meanwhile, 15% of men biopsied with PSAs below 4 are shown to have prostate cancer. As many docs say, “it’s not much, but it’s the best we have” in diagnosing this serious condition. True, but little consolation when you risk losing sexual function as a result of an invasive biopsy which is, in turn, a result of a nebulous lab value.
Anyway, back to my personal example. Why was my body fat test so far off (if in fact it was)? Who knows? I can estimate it on website calculators and get closer to what I think it is. Like this one… where I come in at 8.68% (I do like that number better). With some tests like skinfold and hydrostatic weighing, there is an assumption that the exact same data (skinfold thickness or underwater weight) when applied to older people (I’m 56) reflect a naturally higher body fat for some reason. But when I researched how they actually got the original data they use to estimate body fat, I found that it was largely from autopsies performed in the 1860’s and 1870’s. Not many autopsies have been done for that purpose since. Also, the reference data on skinfold tests and hydrostatic weighing still assumes that as you get older, you automatically lose muscle (regardless of how you eat or how much you work out) and that your skinfold thickness decreases so much that the same lab value at 22 years of age represents twice the body fat at 56. Hey, since 50 is the new 30, maybe those lab values are obsolete, too?
By the way, the gal who administered my body fat test, and who has done thousands of these, had guessed me at 8% before she started the test. She was so flustered by my results, she insisted on doing the test again. And then once again. And then simply handed me my $60 back and said, “I have no explanation, but clearly your test is way off.” Frustrating. But this sort of thing happens every minute of every day in doctors’ offices and clinics throughout the country. Except the doctor doesn’t acknowledge it and you don’t get a refund.
Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.