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Bone Density Scanning (Densitometry) & Body Composition Using DEXA Scan

Updated: Apr 17

Why Your "Life" Really Does Depend On Your Body Composition


Bone Densitometry & Body Composition
Bone Densitometry & Body Composition

We use a lot of tools in medicine to help guide intervention.  Personal history, family history, blood tests, urine tests, toxicity screens, DNA sequencing – you name it.  Medical diagnostics have come a long way.  We have excellent metrics for guiding recommendations when it comes to wellness, but what about recommendations for lifespan?  Healthspan?  These are exciting topics for me personally. They obviously include nutrition, hormones, adequate supplementation, and exercise. But there’s more to measure and learn. So much more, it makes my head spin on most days.

Every one of us is somewhere different on the healthcare journey of life. I have patients in the throes of illness, at the end of their time here on planet earth, true wellness biohackers, and everyone in between. Whether you consider yourself to be sick or well, living long and doing so with the best quality of life possible has to be on your radar or you wouldn’t be here reading this now. Perhaps you’ve already balanced your hormones, optimized your diet, and exercise regularly, but I bet you haven’t even measured the very best predictor of lifespan and healthspan:

Your body composition.


You did that handheld impedance monitor at the gym?  Or you might have a fancy body composition scale at home that updates you every morning?  Maybe you did the full body water dunk tank, or your personal trainer used some calipers to measure the excess skin on the back of your arms?  These tools are readily accessible, but each is riddled with bias.  In the absence of a postmortem analysis, anything we use to approximate what’s more than skin deep is subject to a certain amount of error, but the most accurate test currently available is a dual energy x-ray absorptiometry or ‘DEXA’ scan.

Historically, most people think about DEXA scans to evaluate bone density only, but they can tell us much more than that.  DEXA gives us the most accurate picture of body composition.  You lay on a table, the scanner slowly moves over you, and by using low powered x-rays, the Body Composition using DEXA Scan effectively puts what it sees in your body into one of three categories: bone, fat, and everything else.  From this, we can determine the following four important pieces of information:

  • Total Body Fat

  • Bone Mineral Density (BMD)

  • Visceral Adipose Tissue (VAT)

  • Lean Mass Index

These numbers are compared against a population of people, typically stratified by age and gender.  Generally speaking, boys and girls are different and young people have more favorable body compositions than older ones.  This translates into a wealth of information that helps guide hormone replacement, nutritional supplementation, and exercise recommendations. Before we get into the nuts and bolts of DEXA scanning, let’s address a few concerns and definitions first.

Is Radiation A Concern?

X-rays are in fact radiation. The word ‘radiation’ is kind of a boogey man. We can’t see it, we know it’s potentially harmful, so this part tends to freak people out.  Let me try to put the amount of ionizing radiation from one DEXA scan into perspective.

You’re going to have to geek out with me for a second here.  Radiation is quantified into units.  We call these units ‘millisieverts of radiation’.  The U.S. Nuclear Regulatory Commission (NRC) recommends that a person receive no more than 50 millisieverts of ionizing radiation in any given year.  

Because I can see that the word ‘millisievert’ is making your left eye twitch, from here on out, let’s just refer to these ‘units’ as ‘dollars’, OK?  I know you get dollars, so let’s start over.  

You get $500 dollars to spend on radiation exposure every year.  Got it?  OK.

Just walking around planet earth, the average person at sea level spends roughly $20 dollars on radiation just from exposure to the sun. Not too bad for utilities spending – now you’ve got $480 dollars left.  Let’s say you come down with a cough.  Doc says you need a chest x-ray.  What’s that going to cost?  A regular chest x-ray costs $1 dollar of radiation.  How about a mammogram?  That’s a little more: a mammogram is $4 dollars. Let’s compare that to a CT scan of the chest, abdomen, and pelvis.  This is way more.  Wanna wager a bet? 

One CT chest/abdomen/pelvis = $200 dollars.  Run that scan with and without contrast and you’re pretty damn near your yearly allotment.

CT scans are loads of radiation. Try to steer clear of those unless absolutely necessary.

Back to DEXA scans.  Compared to x-rays, mammography, and CT scans, the ionizing radiation from a single DEXA scan is $.01, or ONE CENT – basically ZERO radiation.  And we aren’t doing these all the time.  Sure, there are people scanning themselves at every weigh in, but that’s not useful.  It takes 6-12 months to see meaningful change in body composition, so I don’t recommend doing them any more frequently than once or twice per year.  

Because things like ‘breakfast’ and ‘water’ get thrown into the ‘everything else’ category, DEXA scans should be done in a fasted state for the best person-to-person comparison.  If you did two scans on the same day – one fasted, the other after Thanksgiving dinner – you would get different results because the scanner can’t subtract those out.  

DEXA Metrics

FAT: Total Body Fat vs VAT

Fat gets a bad rap, but fat isn’t inherently bad. God made fat on purpose. You need fat. We’re supposed to have a certain amount of fat stored in our bodies.  This ‘healthy’ or physiologic fat is also called ‘subcutaneous fat’.  We store it under the skin when we have excess and grab it to burn when we don’t.  Different people have different amounts of subcutaneous fat and different amounts of ability to store it.  By all accounts, this kind of fat has lots to do with how you look in a bathing suit, but little to nothing to do with your overall wellness. 

Total body fat is all the fat in your body – the good and the bad.  Visceral adipose tissue (VAT) is the fat left over once we subtract the subcutaneous fat. This is the bad stuff we care about when we talk about wellness. VAT is highly inflammatory and is indicative of metabolic syndrome and insulin resistance. Insulin resistance is the basic root of all evil. It increases risk for diabetes, heart disease, cancer, and dementia - the Four Horseman.

Your body has a finite amount of healthy space for fat - it's like an NFL football team. You get 53 players. That's it. In the olden days, times were lean. You probably didn't even know 53 members of your tribe let alone 53 who could play football. These days, it seems like everyone wants to play for your team. McDonald's, Dunkin Donuts, Kwik Trip - players are throwing themselves at you left and right. By the time most Americans are in their mid 20s, the majority of them have maxed out their rosters.

For a period of time in history, full fat rosters were a sign of wealth. Go check out paintings in the Louvre - heavy set folks were revered. They laid naked, odalisque style on settees in paintings. But from the prospective of healthy allowable fat stores, your body can only manage so much: 53 players worth, to be precise. If you have more than that in the NFL, you better do some cutting, trading, or injury reserve listing. If you have more than that in human physiology and the body needs to do the same - run it off or starve it off, or put excess amounts somewhere too. Unfortunately, you can't just give it to a friend - it goes into a metabolically dangerous location: Visceral Adipose Fat.

The overage of subcutaneous body fat, is VAT – the most harmful form of extra energy.  Visceral fat gets deposited in and around our organs.  Again, VAT is highly inflammatory.  It plays an active role in insulin resistance, diabetes, heart disease, and cancer. The amount of VAT we have – no matter how small - is highly correlated with increased risk for morbidity and mortality.



What Is A Safe Amount of VAT?

ZERO. Even small amounts of visceral fat stores correlate with increased risk for chronic disease. You can legally have 53 players on your team of fatty players but are you really going to use all of them?  Forget the salary cap – think less is more. Cut out what you don’t need.  It only takes one walk-on to register in the VAT category if your team is already fully loaded.

Can A Person Have Too Much Total Body Fat But Still Be Healthy?

Short Answer: Yes. This is the ‘can I be fat but still be healthy?’ question.  Too much total body fat puts too much excess weight on your joints, correlates with sleep disorders, and drives unwanted inflammation.  BUT – yes, you can technically have a precise, 53-man roster.

Can A Person Have A Low Amount of Total Body Fat But Still Have An Unhealthy Amount of VAT?

Short answer: Yes. This is a much less likely scenario.  Guys don’t typically get bumped off the bench until the bench is already full, but genetics and environmental factors make exceptions to this general rule.  This is one of many reasons why it’s important to know where your individual fat cells are being stored.  

These are important metrics that DEXA scans measure.  It’s fairly easy to eyeball total body fat when looking at a person walking down the street.  Their VAT, however, is often surprising.

Muscle Mass

There are a couple of metrics the DEXA uses to approximate muscle mass, but the appendicular lean mass index (ALMI) likely gives us the most accurate information.  

Now that you’re a grown up, muscles aren’t just for tank tops and bar fights anymore.  Muscle means strength.  Low muscle mass means less strength.  Low levels of lean muscle tissue negatively impacts your ability to sit, stand, walk, recover from a fall, take a shower, drive a car, walk through a grocery store… You get it.  Having enough muscle is critically important when it comes to healthy aging.  Low muscle mass isn’t just a risk for strength related activities, but it can directly impair immune system and organ function as well.  Within reason, you want as much ALMI and as little VAT as possible – especially as you enter your 50s, 60s, 70s, and 80s.

Poor diet, low protein diets, frequent dieting, weight loss, hormone loss, and inadequate exercise correlate nicely with low levels of lean muscle mass. Exactly how much is near impossible to eyeball.  It needs to be accurately measured.

When people lose unnecessary weight, they fortunately lose unnecessary fat. The reality is that they unfortunately lose a certain amount of lean muscle tissue as well.  It is important to know where body composition started and what is happening with changes in total fat, VAT, BMD, and lean muscle mass along the way.  High muscled patients with too much VAT can afford to lose a certain amount of lean tissue as they lose fat.  Low muscled patients need to be monitored much closely and recovered more deliberately when restoring lost lean mass. Any loss of BMD is much more serious.  Let’s discuss that next.

Bone Mineral Density (BMD)

Your bones aren’t just dead blocks of calcium. They are living breathing structures critical for our most basic physiologic functions. The cells in our bones are very much alive and metabolically active.  They are constantly in communication with our kidneys and parathyroid glands which guide the building and breaking down of bone to regulate the circulating levels of important minerals like calcium and phosphorus in the blood. Bone marrow supplies the body with the red blood cells, white blood cells, and platelets needed for healthy immune system function. Our bones provide the structural framework we stand on and walk with every day.  Healthy bones are boss.

What’s the big deal about bone loss?  Well, it’s a really big deal, actually.  Without getting too lost in the weeds, loss of bone equals an increased risk of early death.  As we age, risk for fractures and risk of death from fractures increases exponentially.  Many variables have been studied in this area, but the bottom line is this: Regardless of gender or other co-morbidities, risk of bone loss increases with age, risk of fracture increases with bone loss, and risk of death increases with fractures.  

This seems crazy to even write, but if you are over 65, falls are the #1 cause of accidental death in both genders. Heart disease, cancer, and Alzheimer’s remain the overall top 3 causes of death in the aging population, but after the age of 75, the risk of death from a fall is next in line – and risk of fracture is directly linked to BMD.

Once bone loss has occurred, it is extremely difficult to recover. Your best bet is to measure it early and work to maintain or improve it.

For reasons I simply cannot understand, the United States Preventative Services Task Force (USPSTF), the American Academy of Family Physicians (AAFP), the American Congress of Obstetricians and Gynecologists (ACOG), and the Centers for Disease Control (CDC) do not recommend screening women without ‘risk factors’ for osteoporosis (ie previous history of atypical fracture) until the age of 65. This across-the-board recommendation was made knowing that the biggest risk factor for bone loss in women is menopausal hormone loss, which occurs on average 15 years earlier.  None of these organizations recommend screening men for osteoporosis at all unless they have already had a history of bone fracture.

This makes absolutely no sense to me from a practical or preventative standpoint.  According to more current CDC data (2018), by the age of 65 – the time of their first recommended screening DEXA scan – more than 27% of all women already had osteoporosis.  What the…?? The horse is already out of the barn at 65, ladies.

In general, bone loss follows hormone loss – in both genders.  Bone loss is more gradual in men because hormone loss occurs more gradually in men as they age.  Bone loss in women is more precipitous because hormones essentially just ‘turn off’ in women at the age of 50.  The average age for ‘andropause’, a similar tipping point with respect to hormone loss in men, is roughly the same age - 50.  Why would we wait to screen patients for clinically significant bone loss until they’ve been without their hormones – the biggest supporter of bone density - for 15 YEARS??  And simply never look at men at all unless they’ve already had a fracture? I don’t have a non-sarcastic response to this. It’s just plain negligent.

I don’t think anyone reading this is surprised.  In the end, you are all here because you feel the same way I do: Let’s evaluate for and prevent disease BEFORE that disease declares itself. Your insurance company takes recommendations from our ‘health authorities’, so unfortunately, they won’t cover a bone density scan at the age of 30 or 40, ‘just to make sure your bones are healthy’.  Like all things in the wellness space, we need to take matters into our own hands.

Understanding BMD Results

Bone loss occurs on a continuum. You may have heard these words, ‘osteopenia’ and ‘osteoporosis’. These are just classifications for degrees of bone loss.  By definition, if you have lost 10% of your bone density compared to young matched controls, you have osteopenia.  If you have lost 25% of your BMD compared to young matched controls, you have osteoporosis.  Both are bad.

DEXA results are compared against an age and gender matched control so you can see how your body composition compares to other people your age, but more importantly, how your results compare to those of young healthy people who presumably have the most favorable profiles.  

Z-scores & T-scores

This gives me college statistics PTSD flashbacks.  I didn’t hate many courses I took in college, but stats was one of them.  Ugh.  Thankfully, Z-score and T-score concepts are pretty surface level, so you should be able to understand these without needing any psychiatric intervention.

Z-scores compare your results to a population of people who are your same gender and roughly your same age.

T-scores compare your results to population of people who are your same gender, but are younger and healthier – think ’25 year old version of yourself’.  

When we’re talking about BMD, it’s the T-score that is most useful to look at because what we really want to know is ‘how much bone have you lost compared to your 25-year-old self’.  If you’re a 60-year-woman, comparing your BMD to that of other 60-year-women might give you some bragging rights, but it’s less useful because most other 60-year-old women likely already suffer from postmenopausal related bone loss (recall, 27.1% already have frank osteoporosis at 65). 

A Z-score of 0 means your BMD is dead center of the pack when we compare it to the BMD of other people your age.  If your Z-score is +1.0, it means your BMD is one standard deviation above the mean, which means your bone density is better than 82.5% of other people your age.  If your Z-score is +2.0, it means your BMD is two standard deviations above the mean and better than 97.5% of the population your age.  The same works on the negative side of this.  If your Z-score is -2.0, it means your BMD is lower than that of 97.5% of people your age.

Aside from hormone loss, several factors play a role in risk for bone loss: smoking, current and previous lifestyle, family history, ethnicity, and overall body composition. By current definitions, a T-score of -1.0 to +1.0 is considered ‘normal’, a T-score between -1.0 and -2.5 is considered osteopenia, and a T-score less than -2.5 is defined as osteoporosis.  This is true for both genders.


Measuring and managing body composition is a critical component to wellness.  Unfortunately, elective body comp screening isn’t readily available for most patients who don’t meet the criteria of ‘women over 65’ or ‘men…er, nevermind’. 

FORTUNATELY a state of the art DEXA scanner complete with comprehensive body composition analytics, available to anyone in the community wanting to have their BMD, VAT, and AMLI measured for guidance or for just for fun, recently arrived in a clinic near you. 

Call our office to schedule your DEXA scan with professional interpretation today:)



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