DEXA scan
Accurately knowing our body fat mass, lean mass and bone density
TLDR
I got a DEXA scan to establish baseline measurements for my body composition - fat and lean mass, and bone density. Turns out, I’m not made of sugar and spice
DEXA is more accurate than other measurement methods and can identify important factors that aren’t visible from the outside, like visceral fat and bone mineral density
By distinguishing between fat and lean mass, DEXA metrics provide a much more useful indication of health than your bodyweight
Low bone mineral density is much more common in women than in men. 30-50% of women aged over 50 will suffer from an osteoporosis related fracture
You can take action to improve your fat and lean mass scores as well as your bone density, through the right types of exercise and nutrition
I learned a lot about myself from the DEXA and I’m planning to get another in about 12 months time to see what changes
What’s a DEXA scan?
A DEXA scan (dual-energy X-ray absorptiometry scan) is a full-body scan that accurately measures your body composition, including:
Fat mass, including visceral fat
Lean mass, which includes your muscle mass
Bone mass and bone mineral density
Why did I get one?
Our fat, muscle and bones have a lot to tell us. Put simply, to extend our healthspans, we’re aiming to avoid carrying too much fat while ensuring that we have adequate muscle and strong bones.
DEXA is the gold standard for accurate measurement. It can tell us about our own body composition and how we compare against a large dataset population. It can also reveal critical information that is difficult to otherwise detect - like how much visceral fat you have or how mineral dense your bones are.
I wanted to get a DEXA so I could know where I stand today as a baseline and so I can track my progress over time in response to exercise, diet, ageing and other factors. I also wanted to become aware of any issues that I could unknowingly have, such as high visceral fat or low bone density.
Going in for a DEXA
Getting a DEXA is straightforward. Look for a provider that measures fat and lean mass as well as bone density, as some providers only do the latter. I chose the University of Otago Clinical Research Centre at Wellington hospital.
During the scan, you lie down while a special X-ray machine scans your body in about three minutes. The results are available immediately and the provider explains them to you. Ensure you receive a copy of your results as well as the explanatory notes so that you can review them later, as there’s a fair amount to take in.
The entire appointment takes about 30 minutes and costs $150. Scans aren’t advised if you are pregnant or trying to conceive due to the small amount of radiation involved. It is safe to breastfeed afterward.1
How often will I get a DEXA?
I learned a lot from getting the scan and I intend to repeat the exercise in 12 months, primarily to monitor my fat and muscle mass. For me, an annual check seems about right given the time, expense, minor radiation dose and the ability to monitor using more approximate methods in the meantime.
I don’t feel the need to check bone density as frequently. Over-vigilance has been reported to lead to unnecessary concern and self-misdiagnosis. I’ve now established that I have a normal bone density, and I’d be happy waiting 5-10+ years before another check. You might feel differently if you have a lower density or higher risk factors such as family history or being over 65 years old. As it happens, I’ll find out as a by-product of the fat and muscle mass screening and I’ll be curious to note any changes.
Healthspan insights
Fat
Contrary to what I unfortunately believed in my 20s, fat is not the enemy. But too much fat, especially in the wrong places, is a serious problem.
Women’s bodies are 10-13% essential fat (it’s 2-5% for men), which is vital for our overall health, reproductive health, brain function, metabolism and more.
Additionally, we have storage fat, bringing the total body fat of most women to between 20-30%. Ideally storage fat is found directly beneath the skin and mostly in the hips, thighs and buttocks. Having some storage fat is healthy, serving functions like energy storage, insulation, hormone production and metabolic regulation.
Fat becomes problematic when we accumulate too much and especially when we have too much visceral fat and intramuscular fat. Visceral fat is found in the abdomen around your internal organs. Intramuscular fat is streaked through the muscles. These types of fat are linked to various health problems, including insulin resistance, diabetes, cardiovascular disease, inflammation, cancer and muscle weakness. Both are difficult to see from the outside and a person who doesn’t look fat can nevertheless have dangerous levels of visceral fat.
The two most valuable DEXA fat metrics for healthspan are:
Fat mass index (FMI) - Which measures fat relative to others of your gender and height. It corrects for the flaw in the Body Mass Index (BMI) which is unable to differentiate between fat and lean mass and is therefore unable to differentiate between someone who needs to ‘lose weight’ (read: lose fat) and someone with high muscle. Ideally, you want your FMI to be low in the range.
Visceral fat area (VAT) - A VAT area of above 100cm2 is deemed higher risk. Lower VAT is better, with no known downside to having very low levels.2
Our perceived body shape can be misleading when it comes to fat, so you may be surprised from what you learn in the DEXA.
Taking action - Nutrition is the number one priority for helping us to lower or maintain healthy fat levels, with exercise and other lifestyle factors also able to play a role. Encouragingly, visceral fat is usually lost at a faster rate than overall body fat.
Muscle
DEXA measures lean mass, which includes muscle mass together with your organs, ligaments and connective tissue. It’s a good way of tracking your muscle mass, as changes to total lean mass are largely driven by changes in muscle. As we’ve learned before in Extend, muscle mass is strongly linked to healthspan, so it’s crucial to build and maintain our levels.
DEXA’s Lean Mass Index (LMI) measures lean mass relative to others of your height and gender. Like the FMI, it decouples fat and lean mass to give a much clearer picture than the BMI of whether our weight comprises too much fat or rather a healthy level of muscle.
Higher LMI is generally better, but what constitutes a great result depends somewhat on your natural build. For example, I’m tall and not a particularly muscular person, so it would be unlikely for me to achieve an LMI in the upper quartile.
With an LMI of 15.1, I’m around the 42nd percentile for lean mass - that’s an ok score for me, though it’s desirable for me to increase my LMI further. People with a stockier build should expect to land further up the centiles and might set their sights higher in terms of improvement too.
Taking action: Exercise is the number one priority for muscle mass, especially incorporating adequate strength training. A healthy, balanced diet is also key, including ensuring that you get enough protein to maintain muscle.
Bones
DEXA measures bone mass and mineral density, indicating bone health and strength. Higher bone density means stronger bones, reducing the risk of fractures and osteoporosis.
DEXA provides a bone mineral density score (Z-score for under 50, T-score for 50+), comparing you to your age group or peak bone density in younger years.
Women have less bone mass than men to begin and the difference can be exacerbated by pregnancy, breastfeeding and particularly hormonal changes in menopause. In fact, among all of the diseases that afflict women more than men, osteoporosis is in first place. It’s four times more common in women than men and 50% of women aged over 50 will have an osteoporosis-related fracture in their lifetime. Osteoporosis fractures can be sustained from acts as simple as rolling over in bed. If that’s not a good reason to stay on top of your bone health, I don’t know what is.
DEXA provides a Bone Mineral Density (BMD) score (Z-score for under 50 years, T-score for 50+ years), comparing you to your age group or peak bone density in younger years.
Taking action: Good news, we can strengthen our bones. We need to incorporate weight bearing exercise into our lives - that’s where your skeleton works to bear your weight, as in running, skipping, dancing, ball sports and even walking. Maintaining a nutrient rich diet, including calcium, is also key.3
‘Til next time
I found the DEXA enlightening and I’m looking forward to letting you know if I see any differences 12 months from now.
Radiation protection of patients during DXA, International Atomic Energy Agency https://www.iaea.org/resources/rpop/health-professionals/other-specialities-and-imaging-modalities/dxa-bone-mineral-densitometry/patients#9
For example, my VAT area was estimated at 36cm2, which is well below the 100cm2 threshold. Lower would still be considered better.
It used to be thought that getting enough calcium (the primary mineral in bones), combined with enough vitamin D which is crucial to calcium absorption, was the main priority for bone health. More recently it has been understood that a generally healthy diet as opposed to a diet that is simply rich in calcium or calcium and vitamin D supplementation, offers the best protection.