How to prepare for your DEXA scan
- Oct 17, 2018
- 4 min read
Updated: Jul 7
A Complete Guide for the Most Accurate Result
Whether your goal is to lose body fat, build muscle, improve athletic performance or monitor your health, the value of a DEXA scan lies in its ability to accurately track changes over time. When you're working hard to lose a few kilograms of body fat or gain muscle, even minor differences in scan preparation can affect your results.
Why Preparation Matters
While DEXA is considered the gold standard for measuring body composition, its accuracy still depends on consistent preparation and experienced technicians. At Physique Science, our evidence-based protocols allow us to detect changes in body fat and muscle mass as small as 200–300 g between scans. That's about as precise as body composition assessment gets.
Methods such as bioelectrical impedance, skinfold calipers, air displacement plethysmography (BodPod) and underwater weighing are all influenced by hydration status, recent food intake and testing conditions.
Even with DEXA, differences in preparation can alter your measured body weight, lean mass and body fat percentage. While the scanner itself is highly precise, inconsistent preparation can introduce unnecessary variability between scans.
Our goal is simple: ensure that any changes seen on your results reflect genuine physiological changes—not differences in what you ate, drank or did before your appointment.
When you book in, we’ll send you an email with our recommendations for what to eat and drink in the lead up to your scan including overnight fasting.
How to Prepare for Your DEXA Scan
1. Attend Your Scan After an Overnight Fast
We recommend:
No food after dinner the evening before your appointment.
No coffee, tea, juice, sports drinks, soft drinks, energy drinks or pre-workout supplements.
No water or other fluids on the morning of your scan.
Empty your bladder within the hour before your appointment.
Why?
Everything you consume becomes part of your body mass until it has been digested and processed.
DEXA separates the body into three components:
Bone mineral content
Fat mass
Lean soft tissue (fat-free mass)
Lean soft tissue includes muscle, organs, blood, connective tissue and body water.
The scanner cannot distinguish between muscle tissue and food, fluid or water contained within your digestive system. As a result, recently consumed food and beverages are generally interpreted as lean tissue.
In practical terms, consuming approximately 1 kg of food or fluid before your appointment will usually appear as approximately 1 kg of additional lean mass on your scan.
Arriving fasted provides the most consistent baseline and allows meaningful comparison between future scans.
2. Stay Well Hydrated the Day Before
Although we recommend fasting on the morning of your appointment, it is important to be well hydrated the day before.
Aim to drink water regularly throughout the day and consume approximately one to two glasses of water with meals and snacks.
Why?
Hydration significantly influences lean tissue measurements.
Dehydration reduces total body water, while overhydration increases it. Since DEXA measures all body water as part of lean soft tissue, changes in hydration status can affect your lean mass measurement independent of any actual change in muscle tissue.
Maintaining normal hydration helps ensure consistent results.
3. Eat Normally the Day Before
Avoid crash dieting or severely restricting carbohydrates immediately before your scan.
Instead, consume your usual diet with an appropriate intake of quality carbohydrates.
Why?
Muscles store carbohydrate in the form of glycogen.
Each gram of glycogen is stored alongside several grams of water. If glycogen stores become depleted through prolonged dieting or carbohydrate restriction, your muscles also lose water.
Because DEXA measures both muscle tissue and its associated water as lean mass, depleted glycogen stores can reduce your measured lean mass by several hundred grams—and in some cases close to one kilogram.
Normal eating before your scan provides the most representative picture of your usual body composition.
4. Avoid Exercise Before Your Appointment
We recommend avoiding training on the morning of your scan.
If possible, avoid particularly strenuous exercise the evening before your appointment as well.
Why?
Exercise changes muscle glycogen levels, hydration status and fluid distribution throughout the body.
These temporary physiological changes can influence lean tissue measurements, making it more difficult to compare one scan with another.
For the most accurate assessment, attend your appointment before completing your daily training session.
5. Wear Clothing Without Metal
Please wear comfortable clothing free of:
Metal zips
Underwire bras
Buttons
Studs
Clips
Jewellery where possible
Disposable gowns are available if required.
What If I Can't Fast?
We understand that fasting is not always practical.
If you need to eat or drink before your appointment, simply let our team know.
For clients who are monitoring changes over time, consistency is far more important than perfection.
If your pre-scan meal is similar before each appointment—for example, the same bowl of oats and cup of coffee—it allows us to compare future scans under similar conditions and interpret any changes more accurately.
Why We Take Preparation Seriously
Every DEXA scanner is affected by food intake, hydration and exercise. These are not limitations unique to our equipment—they are inherent physiological factors that influence every body composition assessment.
The difference is that at Physique Science, we understand these variables and have developed standardised preparation protocols to minimise their impact.
By following the preparation guidelines, we can detect relatively small changes in body fat and lean mass with greater confidence and provide results that are meaningful from one scan to the next.
Frequently Asked Questions
Can I have coffee before my DEXA scan?
No. We recommend avoiding all caffeinated beverages, including coffee, tea, energy drinks and pre-workout supplements. Caffeine may alter hydration status and introduces unnecessary variability between scans.
Can I drink water before my scan?
We recommend arriving after an overnight fast without drinking on the morning of your appointment. Instead, ensure you are well hydrated the day before.
Why do I need to empty my bladder?
A full bladder contributes additional body weight and lean mass to your scan. Emptying your bladder before your appointment improves consistency.
Should I exercise before my scan?
No. Complete your DEXA scan first, then train afterwards whenever possible.
Book Your DEXA Scan Brisbane
If you have any questions before your appointment, our team is always happy to help.
Book your DEXA Scan Brisbane appointment with Physique Science today and experience body composition testing performed with research-backed protocols and industry-leading expertise.
