Know What You Are Actually Made Of: The Case for DEXA Scanning
Most of us have a reasonable sense of whether we are healthy. We know roughly what we weigh. We have a sense of our fitness level. We get blood work done periodically and review the results with our physician. What most of us do not have is any direct measurement of what our bodies are actually made of: how much of our weight is muscle, how much is fat, where that fat is distributed, and how dense our bones are. A DEXA scan answers all of these questions in a single, low-radiation, non-invasive test that takes less than twenty minutes. It is one of the most informative and underutilized tools in preventive medicine, and in a proactive longevity medicine practice, it is among the first tests we recommend.
The Problem With BMI
Before discussing what a DEXA scan reveals, it is worth addressing the measurement most of us rely on instead: BMI, or body mass index. BMI is calculated by dividing weight in kilograms by height in meters squared. It is simple, requires no equipment, and has been the cornerstone of population-level health screening for decades.
It is also, as a tool for evaluating individual health, deeply inadequate.
BMI tells us nothing about what our weight is composed of. A highly trained athlete with substantial muscle mass and very low body fat will frequently register as overweight or even obese by BMI, while a sedentary individual with very little muscle and significant fat accumulation may register as perfectly normal. The number reflects total mass relative to height, and nothing else. It cannot distinguish between a pound of muscle and a pound of fat, and it has no awareness whatsoever of where fat is located in the body, which, as we will discuss, is one of the most clinically important questions in metabolic health.
BMI emerged as a statistical tool for analyzing population trends, not as a diagnostic instrument for individual patients. Using it to assess an individual's health risk is a bit like using the average height of a country's population to determine whether a specific person can reach a high shelf. It may tell you something at a group level. It tells you remarkably little about the person in front of you.
This is not a fringe position. Major medical organizations have increasingly acknowledged BMI's limitations, and the conversation in clinical medicine has been shifting toward direct body composition measurement for years. The problem is that better tools require equipment and take more time, which is why BMI has persisted in settings where neither is available. In a practice focused on precision and prevention, that trade-off is not acceptable.
Bone Health Is Not Just a Problem for the Elderly
When most people hear the word osteoporosis, they picture an elderly woman with a stooped posture, not a forty-year-old professional or a thirty-five-year-old athlete. That association is understandable, but it has led to a serious blind spot in how we approach bone health.
The critical window for building bone mass occurs earlier in life than most people realize. Approximately 90% of adult bone mass is typically attained by ages 18 to 21 in females and 20 to 23 in males. After that point, we begin a slow process of net bone loss that accelerates in midlife and beyond. The implication is significant: the bone density you carry into your forties and fifties is largely determined by what you built in your teens and twenties, and what you protect in the decades that follow.
Peak bone mass is regarded as one of the most important determinants of osteoporosis and fracture risk later in adulthood. The problem is that bone loss is entirely silent. There are no symptoms, no warning signs, and no way to detect it without imaging. By the time a fracture occurs, significant bone loss has typically been underway for years.
Current screening guidelines recommend DEXA scans for women at age 65 and men at age 70. For a patient who has been losing bone density since their thirties, this is extraordinarily late. Earlier evaluation is warranted in individuals with identifiable risk factors, but the definition of those risk factors in standard guidelines is narrow. Low dietary calcium, sedentary behavior, family history, low body weight, smoking, and prolonged stress are all contributors that are common in otherwise healthy, high-functioning adults. In our practice, we do not wait for a fracture or an arbitrary age threshold to establish a baseline. We want to know where a patient stands while there is still time to meaningfully intervene.
The good news is that bone density responds to intervention. Resistance training, adequate protein intake, calcium and vitamin D optimization, and in appropriate cases pharmacological treatment can all arrest or reverse bone loss, but only if we know it is happening. A DEXA scan is how we find out.
The "Skinny Fat" Problem: What the Scale Misses
Visceral fat, the fat that accumulates around the abdominal organs rather than beneath the skin, is metabolically distinct from subcutaneous fat and significantly more dangerous. Thirty years of epidemiological research have established that visceral adipose tissue is an independent risk marker of cardiovascular and metabolic morbidity and mortality. It releases inflammatory compounds and hormones that impair insulin signaling, disrupt lipid metabolism, and accelerate atherosclerosis in ways that subcutaneous fat does not.
What makes this clinically urgent is that visceral fat accumulation is not reliably visible and is entirely missed by standard weight and BMI measurements. BMI in isolation cannot account for the extreme variation in intra-abdominal fat distribution between individuals. The patient who appears lean by every conventional measure can carry a visceral fat burden that places them at significantly elevated metabolic and cardiovascular risk, a phenomenon increasingly referred to as "metabolically obese, normal weight," or more colloquially, "skinny fat."
The research on this is striking. Studies have found that individuals with normal weight but excess visceral fat can carry more than two to three times the cardiovascular disease risk of individuals who are heavier by BMI measures but carry less visceral fat. Being thin does not protect you if your fat is in the wrong place, and being heavier by the scale does not necessarily put you at higher risk if your body composition is favorable.
A DEXA scan provides a direct measurement of visceral fat area, identifying patients who would otherwise appear healthy by conventional metrics but are carrying a hidden metabolic risk that warrants intervention. This is information that cannot be obtained from a scale, a tape measure, or a standard blood panel. It requires imaging, and DEXA is the most accessible and practical way to get it.
Muscle Asymmetry: What Your Bilateral Lifts Are Hiding
For patients who are actively engaged in resistance training, a DEXA scan provides one additional layer of information that most people are not thinking about: the distribution of lean muscle mass between the left and right sides of the body.
As discussed in a previous post on building a more complete fitness plan, bilateral exercises allow the dominant side to quietly compensate for the weaker one. A squat, a deadlift, and a bench press all involve both sides of the body working together, which means significant left-right asymmetries can develop and persist for years without being detected. These asymmetries are not merely a performance issue. They alter movement mechanics, place unequal stress on joints, and are a significant contributor to overuse injuries and chronic musculoskeletal pain.
DEXA scan results segment lean mass by limb, providing a clear picture of whether meaningful asymmetry exists between sides. For an athlete preparing for competition, this information is directly actionable. For a patient who cannot understand why one shoulder, one knee, or one hip keeps causing problems, it may be the missing piece of the diagnostic picture.
Addressing identified asymmetries means prioritizing unilateral training: single-leg exercises, single-arm movements, and movements that force each side of the body to perform independently. As a secondary benefit, unilateral exercises demand substantially greater core engagement than their bilateral counterparts, which translates over time to improved postural stability and reduced risk of chronic back pain. The DEXA finding becomes the clinical rationale for a training adjustment that the patient now has a concrete reason to make and stick to.
What a DEXA Scan Actually Measures
A single DEXA scan provides:
Bone mineral density at the hip, spine, and whole body, reported as a T-score comparing you to peak young adult bone mass and a Z-score comparing you to age-matched peers
Total body fat percentage, including regional breakdown by trunk, arms, and legs
Visceral fat area, the most clinically significant body composition measurement for metabolic health
Lean muscle mass, segmented by region and by side, allowing identification of meaningful asymmetries
Resting metabolic rate estimation, derived from lean mass measurements
The scan delivers a radiation dose that is negligible, roughly equivalent to a few hours of natural background radiation, and takes less than twenty minutes to complete. For the volume of clinically actionable information it provides, there is no comparable test.
How Often Should You Scan?
For most patients, an annual DEXA scan provides a meaningful longitudinal picture of how bone density and body composition are changing over time. This cadence is particularly important for patients who are actively working to build bone density, reduce visceral fat, or correct a muscle asymmetry, since the feedback loop of knowing whether the interventions are working is itself a powerful motivator. For patients with stable, favorable results, every two years is a reasonable interval. The right frequency is ultimately a conversation to have with your physician based on your individual risk profile and goals.
The Bigger Picture
A DEXA scan will not tell you everything about your health. But it will tell you things that nothing else can: whether your bones are quietly losing density before a fracture makes that obvious, whether your body composition carries a metabolic risk your weight does not reveal, and whether the training you are doing is building a body that is symmetrical and resilient or one that is compensating in ways that will eventually cause problems.
In longevity medicine, the goal is not simply to treat disease when it appears. It is to understand your body well enough to protect it before problems develop. A DEXA scan is one of the most practical ways to do exactly that.
Dr. Schraga is a concierge physician at Crescendo MD, a longevity-focused concierge medicine practice serving the San Francisco Bay Area. He specializes in personalized preventive care, executive health, and longevity medicine for high-performing individuals and families.
