A morning appointment slip sits beside a glass of water and a cup of coffee. Coffee before a fasting blood test? Choose plain water instead.
Fasting usually means no food or drinks except plain water for the time your provider has specified.
Plain water versus other drinks
Plain water: Allowed during a fasting instruction. It helps you stay hydrated without adding substances from a drink to your bloodstream.
Coffee, tea, juice and fizzy drinks: Not part of the fast. Food and drinks can add substances to the bloodstream and may change some test results.
Why the difference matters
Think of fasting as keeping the starting line the same for a test. This is only a simple comparison: each blood test has its own preparation rules.
The fasting time is commonly 8 to 12 hours, but the exact time depends on the test ordered. Not every blood sugar test needs fasting, so check the instructions you were given.
For more detail, see MedlinePlus: Fasting for a Blood Test.
Remember
“Fasting” does not simply mean skipping breakfast; it also changes what you drink. Do not fast unless your provider or test instructions say that you should.
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This article is for general education and does not replace personalised advice from a qualified healthcare professional.