7 Things You Should Never Do Before a DEXA Scan

A DEXA scan is one of the most accurate tools available for measuring body composition. However, the accuracy of your results depends heavily on how consistently you prepare for each scan.

If your goal is to track changes in body fat, muscle mass, or visceral fat over time, avoiding the following mistakes will help ensure your results reflect actual changes in your body rather than differences in testing conditions.

1. Don't Eat or Drink Before Your Scan

Food, fluids, protein shakes, sports drinks, coffee, and other caffeinated beverages all add weight to your body and can influence body composition measurements.

For the most consistent results, arrive fasted with no food, fluids, or caffeine before your scan.

2. Don't Exercise on the Day of Your Scan

Avoid all exercise before your DEXA scan, not just strenuous exercise.

Exercise can temporarily alter:

• Hydration status

• Muscle glycogen stores

• Fluid distribution throughout the body

• Measured lean mass

• Measured fat mass

• Visceral fat estimates

Unlike food and fluid intake, the effects of exercise are difficult to predict. There is no simple gram-for-gram adjustment that can account for how exercise influences a scan.

Some people assume they can simply perform the same workout before every scan to standardise results. Unfortunately, this is rarely possible. Factors such as workout intensity, recovery status, environmental temperature, humidity, and even seasonal differences between summer and winter can influence the body's response to exercise and the resulting scan measurements.

For this reason, avoiding exercise on the day of your scan is the most reliable approach.

3. Don't Use Saunas, Hot Baths or Other Sweating Strategies

Avoid saunas, hot baths, excessive sweating, or deliberate dehydration strategies before your scan.

These practices reduce total body water, which can lead to a lower measured lean tissue mass on your DEXA scan. This may create the appearance that you have lost muscle when, in reality, the change is simply due to altered hydration status.

If you arrive dehydrated following a sauna, hot bath, or heavy sweating session, your scan may show:

• Lower lean mass

• Lower body weight

• Potential changes in body fat percentage

When comparing scans over time, differences in hydration can make it difficult to determine whether changes reflect actual changes in body composition or simply temporary shifts in body water.

4. Don't Significantly Change Your Carbohydrate Intake Before a Review Scan

Carbohydrates are stored in the body as glycogen, primarily within muscle and liver tissue. Glycogen is stored alongside water, meaning changes in carbohydrate intake can affect both body weight and measured lean mass.

When returning for a repeat scan:

• Aim to consume a similar amount of carbohydrate to what you were consuming before your previous scan.

• If your carbohydrate intake has been substantially lower than normal, return it to a level similar to your previous scan before retesting.

• Avoid deliberately restricting carbohydrates or carbohydrate loading immediately before the scan.

Large differences in carbohydrate intake between scans can alter glycogen and associated water stores, making it difficult to determine whether changes in lean mass reflect true muscle gain or simply differences in fuel and hydration status.

5. Don't Wear Clothing with Metal

Metal can interfere with the scan image.

Avoid:

• Underwire bras

• Belts

• Watches

• Jewellery

• Clothing with large metal zips

Your clinic will advise you if anything needs to be removed before the scan.

6. Don't Compare Results from Different DEXA Machines

This is one of the most common mistakes people make when tracking body composition.

Different DEXA manufacturers use different hardware, software, algorithms, and reference databases. As a result, measurements such as body fat percentage, lean mass, fat mass, and visceral fat can differ between machines even when your body has not changed at all.

For the most meaningful comparisons, use the same DEXA machine whenever possible.

7. Don't Have Other Imaging Procedures Before Your DEXA Scan

Avoid having other imaging procedures that involve contrast agents or radioactive tracers in the 24–48 hours before your DEXA scan.

This may include:

• CT scans with contrast

• Nuclear medicine scans

• PET scans

• Barium studies

Contrast materials and radioactive tracers can remain within the body for a period of time and may appear on the DEXA image. This can interfere with image interpretation and, in some cases, affect the accuracy of body composition measurements.

If you have recently undergone one of these procedures, let your DEXA clinic know before your appointment. They may recommend postponing your scan until the contrast material or tracer has cleared your system.

Consistency Is Everything

The value of a DEXA scan lies in its ability to track change over time. To get the most reliable results:

• Fast before your scan (no food, fluids, or caffeine)

• Avoid exercise on the day of your scan

• Avoid saunas, hot baths, and dehydration strategies

• Maintain a consistent carbohydrate intake before repeat scan

• Arrive in a similar hydration state each time

• Use the same DEXA machine for follow-up scans

The more consistent your preparation, the more confident you can be that changes in your results reflect real changes in body composition—not differences in testing conditions. A DEXA scan is a powerful tool, but only when the conditions surrounding each scan are as consistent as possible.