When you are trying to lose body fat, build muscle or improve your health, bathroom scales only tell you part of the story. Your weight may remain unchanged even while you lose fat and gain muscle. This is why body composition testing can provide much more useful information than body weight or Body Mass Index (BMI) alone.
However, not all body composition tests work in the same way. DEXA scans, InBody machines, smart scales and skinfold measurements can produce noticeably different results—even when they are performed on the same person.
So, which body composition test should you trust?
In this guide, we compare DEXA scans with InBody testing, bioelectrical impedance smart scales and skinfold callipers. We also explain what a DEXA scan measures, who may benefit from one and where you can have a DEXA body composition scan on Sydney’s Northern Beaches.
What is body composition?
Body composition describes what your body is made of rather than simply how much it weighs. Depending on the assessment method, it may include:
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Total fat mass
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Body fat percentage
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Lean mass
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Regional fat and lean-mass distribution
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Visceral fat estimates
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Bone mineral content
Two people can have the same height and weight but very different body compositions. One may have more muscle and less body fat, while the other may have less muscle and more body fat. Their BMI could be identical despite meaningful differences in their physical health, strength and metabolic risk.
Body composition testing can provide a better baseline for monitoring changes associated with exercise, nutrition, rehabilitation or healthy ageing.
What is a DEXA body composition scan?
DEXA stands for dual-energy X-ray absorptiometry. It may also be written as DXA. The scanner passes two very low-dose X-ray beams through the body. Different tissues absorb these beams differently, allowing the system to estimate fat mass, lean soft tissue and bone mineral content.
DEXA is a validated method of assessing body composition and is widely used in clinical practice and research. Unlike scales that provide only whole-body estimates, a DEXA scan can show how fat and lean mass are distributed across different regions of the body.
A DEXA body composition report may include:
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Total body fat percentage
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Total fat mass
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Total lean mass
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Fat and lean mass in the arms, legs and trunk
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Differences between the left and right sides
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Android and gynoid fat distribution
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An estimate of visceral fat
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Bone mineral content
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Estimated basal metabolic rate
It is important to understand that “lean mass” does not mean muscle alone. It includes muscle and other non-fat, non-bone tissue. However, monitoring regional lean mass can still be extremely useful when assessing training progress, rehabilitation and changes between different areas of the body.
DEXA scan vs InBody: what is the difference?
InBody machines use bioelectrical impedance analysis, commonly known as BIA. A small electrical current travels through the body, and the machine uses the resistance encountered to estimate body water, fat-free mass and body fat.
The test is quick and convenient, which makes it popular in gyms and fitness centres. However, it does not directly measure body fat or muscle. Its results are calculated using electrical impedance and prediction equations.
Hydration can significantly affect these estimates. Recent exercise, food intake, alcohol, carbohydrate consumption, sweating and even the time of day can change the amount and distribution of water in the body. This may cause an apparent change in fat or muscle that does not reflect a genuine change in body tissue.
DEXA also involves calculations and has limitations, but it measures tissue attenuation using X-rays rather than relying mainly on body water and electrical resistance. It also provides detailed regional information that many BIA devices cannot provide with the same level of confidence.
| Feature | DEXA scan | InBody/BIA |
|---|---|---|
| Technology | Dual-energy X-rays | Electrical impedance |
| Measures | Fat, lean tissue and bone mineral | Estimates based largely on body water |
| Regional analysis | Detailed | Model-dependent |
| Affected by hydration | Somewhat | More substantially |
| Visceral fat | Estimate based on scan data | Prediction |
| Bone information | Bone mineral content within the body-composition analysis | Not directly measured |
| Convenience | Requires specialised equipment | Widely available |
| Best use | Detailed baseline and progress assessment | Convenient general trend monitoring |
For someone who wants a detailed and repeatable baseline, DEXA will generally provide more useful information. InBody can still help monitor general trends, particularly when every test is completed under very similar conditions.
DEXA scan vs smart scales
Most smart bathroom scales also use bioelectrical impedance. The electrical current usually travels up one leg and down the other, although some advanced models also include hand electrodes.
A smart scale can be useful for regularly monitoring body weight. Its estimated body-fat percentage, muscle mass, metabolic age and visceral fat rating should be interpreted more cautiously.
Changes in hydration may cause the displayed body-fat percentage to rise or fall over a short period. The scale’s software may also use age, sex, height and weight to predict results based on population averages. This means two people with different body compositions can sometimes receive similar estimates.
Smart scales are convenient for watching long-term trends, but they should not be treated as equivalent to a clinical body composition assessment.
DEXA scan vs skinfold measurements
Skinfold testing uses callipers to measure the thickness of subcutaneous fat at selected sites. These measurements are entered into an equation to estimate overall body fat.
When performed by a highly experienced practitioner, skinfold testing can be useful for monitoring changes over time. It is relatively inexpensive and does not involve radiation.
Its accuracy depends heavily on:
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The practitioner’s technique
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The sites measured
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The equation used
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The person’s age, sex and body-fat distribution
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Whether exactly the same method is used each time
Skinfold testing only measures fat beneath the skin. It does not directly assess visceral fat, lean-mass distribution or bone mineral content. It may also be less suitable for people whose body shape or body-fat level falls outside the population used to create the prediction equation.
Why your weight can stay the same while your body changes
One of the greatest benefits of DEXA scanning is its ability to show changes that ordinary scales may miss.
Imagine that over three months you lose three kilograms of fat while gaining three kilograms of lean mass. Your total weight would be unchanged. If you only watched the bathroom scales, you might assume that your exercise and nutrition program had failed.
A follow-up body composition scan may instead show meaningful improvements in fat mass, lean mass and fat distribution. This can help you assess whether your program is working and make better-informed adjustments.
The reverse can also happen. A person may lose weight quickly but lose a combination of fat and lean tissue. Although the number on the scales has decreased, the result may not be ideal for strength, function or long-term health.
Who can benefit from a DEXA body composition scan?
A DEXA scan may be particularly useful for:
People trying to lose body fat
DEXA provides a detailed starting point and allows you to monitor whether weight loss is coming primarily from fat, lean tissue or both.
People trying to build muscle
Regional results can help identify changes in lean mass throughout the arms, legs and trunk. They may also reveal meaningful differences between the left and right sides.
Athletes and recreational exercisers
Body composition can influence performance, recovery and training decisions. A baseline scan provides objective information that can be reviewed alongside strength, fitness and performance testing.
People returning from injury or surgery
Periods of pain, reduced activity or immobilisation can contribute to loss of lean mass. Regional DEXA information may help monitor changes during rehabilitation, although it does not replace a physical assessment by a physiotherapist or exercise physiologist.
Older adults
Maintaining muscle and bone health becomes increasingly important with age. Body composition information can assist conversations about resistance exercise, nutrition and healthy ageing.
Anyone frustrated by ordinary scales
If your weight is not reflecting changes in your clothing, strength, appearance or fitness, a body composition scan may provide a clearer explanation.
Is a body composition DEXA the same as a bone density scan?
No. A whole-body DEXA body composition scan and a diagnostic bone mineral density scan are different assessments.
A body composition scan analyses fat mass, lean mass and bone mineral content across the whole body. It may provide general information about bone mineral content, but it should not be used to diagnose osteoporosis or osteopenia.
A diagnostic bone density scan specifically examines areas such as the lumbar spine and femoral neck. These measurements are used to calculate T-scores or Z-scores and assess bone health and fracture risk.
If you want information about both body composition and diagnostic bone density, the appropriate separate scans should be performed.
How to prepare for a DEXA body composition scan
Consistency improves the value of repeat testing. For the most meaningful comparison:
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Use the same scanner and facility each time
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Book follow-up scans at a similar time of day
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Maintain a similar hydration and food routine beforehand
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Avoid unusually strenuous exercise immediately before testing
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Wear light clothing without metal where possible
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Tell the practitioner if you may be pregnant
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Follow any preparation instructions provided by the clinic
Try not to overreact to very small changes between scans. No body composition method is perfectly exact, and normal biological variation can influence results. The most useful information usually comes from meaningful trends measured under consistent conditions.
How often should you have a body composition scan?
Scanning too frequently can make normal short-term variation appear more important than it is. For many people, approximately eight to twelve weeks allows enough time for measurable changes to occur, although the appropriate interval depends on your goals and program.
A baseline scan before beginning a new exercise or nutrition plan, followed by another scan after a structured training period, can provide a practical comparison.
DEXA body composition scanning in Mona Vale
Holistic Physio Fitness provides DEXA body composition scanning at 84 Barrenjoey Road, Mona Vale, on Sydney’s Northern Beaches.
Our scans are performed by qualified physiotherapy and exercise physiology professionals. Your results can be explained in the context of your exercise, nutrition, rehabilitation and health goals rather than simply being handed to you as a page of numbers.
The scan itself is quick, painless and non-invasive. You remain still on a padded scanning table while the scanning arm passes over your body. Your results are then available for explanation.
DEXA appointments must be booked by telephone and cannot currently be booked through the online appointment system. To enquire or make an appointment, call 02 9999 6666.
Frequently asked questions
Is DEXA more accurate than an InBody scan?
DEXA is generally considered a more detailed and robust method of assessing body composition. InBody uses bioelectrical impedance and can be influenced by hydration, recent exercise and food intake. DEXA uses low-dose X-rays to differentiate fat, lean tissue and bone mineral, while also providing detailed regional results.
Does a DEXA scan measure visceral fat?
A body composition DEXA scan can provide an estimate of visceral adipose tissue in the abdominal region. This is more informative than total body weight alone, although it remains an estimate and should be considered alongside other health information.
Can DEXA tell me exactly how much muscle I have?
DEXA reports lean soft tissue rather than directly isolating skeletal muscle. Lean mass includes muscle and other non-fat soft tissues. Regional lean-mass results are nevertheless valuable for monitoring training, rehabilitation and differences between areas of the body.
Is a DEXA scan painful?
No. A DEXA scan is painless and non-invasive. You lie still on a padded table while the scanning arm moves above your body.
Do I need a referral for a body composition DEXA scan?
A referral is generally not required for a body composition scan at Holistic Physio Fitness. Diagnostic bone density assessments and individual health circumstances may have different requirements, so contact the clinic if you are unsure.
Where can I book a DEXA scan on the Northern Beaches?
Holistic Physio Fitness provides DEXA body composition scanning at 84 Barrenjoey Road, Mona Vale. Call 02 9999 6666 to enquire or book, as DEXA scans cannot currently be booked online.
Get a clearer picture of your progress
Body weight alone cannot tell you whether you are losing fat, building muscle or changing the distribution of tissue throughout your body. Although smart scales, InBody machines and skinfold measurements can all have a place, DEXA provides one of the most comprehensive practical assessments of body composition available.
If you want an objective baseline or a more meaningful way to measure progress, contact Holistic Physio Fitness in Mona Vale on 02 9999 6666 to arrange your DEXA body composition scan.