Understanding Your Body Composition Scan: What Your Numbers Mean and What to do Next
A Bioelectrical impedence Analysis (BIA) or, the Gold-standard, Dexa Scan can provide insights into your body composition.
A body composition scan is a useful way to get a snapshot of what your body is made up of - not just how much you weigh. Rather than focusing solely on the number on the scale body composition testing can help us understand your muscle mass, body fat percentage and distribution, hydration, and more.
The goal of this assessment isn't to achieve a particular number on every metric. Instead, your results can help identify areas where exercise, nutrition, and approaches like Physiotherapy may be able to improve your health, strength, and physical functioning.
Body Fat and Fat-Free Mass
Body fat percentage tells us simply what proportion of your total body weight is fat, also known as adipose tissue. Having a body fat within an expected arange is important for hormone function, energy storage, and overall health. Additional body fat, particularly around the abdomen, can increase health risks.
Fat-free mass is everything that isn't body fat. This includes muscle, bone, organs, connective tissue, and water. A higher percentage of fat-free mass generally indicates that a greater proportion of your body weight is made up of lean tissue.
From a Physiotherapy perspective, maintaining or increasing muscle mass is generally a positive goal, particularly as we age. Strength training, adequate protein intake, and regular physical activity can all help preserve or increase lean mass.
Looking at Muscle and Fat Distribution
A body composition scan can show lean mass and fat mass by body segment—such as your left and right arms, legs; and trunk.
This can be particularly interesting when looking at side-to-side differences. For example, someone recovering from a prolonged knee injury or surgery may have noticeably less lean mass in one leg due to deconitioning from a period of time where they could not exercise their muscles as much as the opposite side. Tracking this over time can provide an objective measure of recovery, alongside strength testing and functional assessments.
Segmental fat analysis shows where fat is distributed throughout your body. While some asymmetry is completely normal, large differences or notable trunk fat may provide useful information when considering your overall health and exercise strategy.
Visceral fat is fat stored around your internal abdominal organs. Unlike the fat just underneath the skin, higher levels of visceral fat are associated with increased metabolic and cardiovascular health risks. Reducing visceral fat is often best addressed by a combination of regular aerobic exercise, resistance training, appropriate nutrition, adequate sleep, and sustainable lifestyle habits—not through trying to rapidly lose weight.
Basal Metabolic Rate
Your basal metabolic rate (BMR) is an estimate of how much energy your body requires at rest to maintain essential functions such as breathing, circulation, and organ function.
BMR tends to be higher in people with more lean mass because muscle and other lean tissues have greater baseline energy requirements. This is one reason why resistance training can be an important component of long-term weight management and healthy aging.
Intra- and Extracellular Water
Water held in your body is broadly divided into intracellular water (ICW) and extracellular water (ECW).
Intracellular water is the water contained inside your cells. Muscle cells, for example, contain a substantial amount of water.
Extracellular water is the water outside your cells, including fluid in your blood and the spaces surrounding your cells.
The relationship between these two measurements can provide useful information about hydration and fluid distribution. The ECW/TBW ratio (extracellular water divided by total body water) is often more useful than either number alone. Changes over time may be worth investigating, particularly when they occur alongside swelling, injury, illness, or changes in training.
What Should You Do With Your Results?
These scans are useful because they help identify meaningful areas for improvement. It’s helpful to get in touch with members of your healthcare team to get advice from registered health professionals as to your next steps.
Depending on your individual results and goals, your Physiotherapist may recommend increasing resistance training, focusing on cardiovascular fitness, addressing a side-to-side strength or muscle-mass difference, increasing daily activity, or modifying an exercise program following an injury.
Final Thoughts
What can affect your results?
Hydration is one of the biggest factors, as drinking significantly more or less fluid than usual can affect estimates of body water, lean mass, and body fat.
Food and drink consumed shortly before a scan can also temporarily increase body weight and alter fluid distribution.
Recent exercise, particularly strenuous exercise, can shift fluid between different parts of the body and change circulation, while sweating can affect hydration levels.
Alcohol consumption can also influence hydration and fluid balance.
Your time of day can also matter because body weight and fluid distribution naturally fluctuate throughout the day.
For people who menstruate, hormonal changes throughout the menstrual cycle can cause temporary changes in body weight and fluid retention.
Sleep quality is less likely to directly change the measurement but can indirectly affect hydration, stress levels, appetite, and activity levels.
Other factors - including having a full bladder, recent illness, fever, vomiting or diarrhea, a recent sauna or hot tub, and changes in skin temperature - can also influence the results. Even clothing can introduce small differences between measurements.
For these reasons, if you're using these scans to track progress, consistency is more important than achieving perfect testing conditions. Whenever possible, try to have your scans performed at a similar time of day, with similar hydration and food intake, and under similar exercise and clothing conditions. Most importantly, look at trends over time rather than focusing on one individual result. A small change in body fat or lean mass between two scans does not necessarily represent a true change in your tissues—it may simply reflect normal day-to-day variation. When changes are consistent across multiple scans and are accompanied by improvements in strength, fitness, mobility, or physical function, they become much more meaningful.
How often should you have an body composition scan?
For most people, repeating a scan every 8–12 weeks provides a good balance between giving your body enough time to make meaningful changes and allowing you to track your progress regularly.
If you're completing a structured rehabilitation or strength-training program, a scan after approximately 6–8 weeks can provide useful feedback, while people using primarily for general health monitoring may only need to test every 3–6 months.
More frequent testing isn't necessarily more useful, as normal fluctuations in hydration, food intake, exercise, and fluid distribution can make short-term changes difficult to interpret. The goal is to look for meaningful trends over time, ideally alongside changes in strength, mobility, fitness, and physical function.
- Thanks for reading and keep looking for more posts in the future on other ‘hot topics’ in the world of Physiotherapy and Physical Rehabilitation!
