Why you should fast and skip caffeine before a DEXA scan
- 3 hours ago
- 2 min read
At Physique Science, we recommend attending your DEXA scan after an overnight fast, meaning no food, fluids, coffee, tea, energy drinks, pre-workout supplements, juice, soft drink, sports drinks, or other beverages.
The reason is simple: we want your results to be as accurate and consistent as possible.
When you eat or drink before a scan:
Food and fluid add weight that becomes part of your total body mass.
Food and drink sitting in your stomach and intestines can alter estimates of lean mass and body fat percentage.
Drinking fluids before a scan can increase measured lean tissue mass because DEXA cannot distinguish between muscle tissue and the water contained within tissues.
Caffeine-containing beverages may also affect hydration status and introduce additional variability between scans.
In simple terms, 1 kg of food or fluid consumed before your scan will generally appear as approximately 1 kg of lean mass on the DEXA scan.
The real value of DXA is comparing scans over time. Most people only have a scan every few months and often cannot remember exactly what they ate, drank, or how hydrated they were before their previous appointment.
By asking everyone to attend in a fasted state, we create a consistent starting point for every assessment and minimise measurement error. This helps ensure that changes in your results reflect genuine changes in body composition rather than differences in recent food, fluid, or caffeine intake.
It also reduces the risk of disappointment or confusion when interpreting results, allowing us to be more confident that any changes seen are real.
For the most reliable results, we recommend attending your DEXA scan after an overnight fast, and having emptied your bladder within the hour before your scan.
