You can consume nothing but water for at least 8 hours before a fasting glucose test. You may also need to follow a low carb diet and avoid exercise for some time before.
A fasting glucose test measures your glucose level after not eating for at least 8 hours. Here are some guidelines and tips to help ensure you’re fully prepared for the test and you get the most accurate results.
The following tips can help ensure a successful test with as little difficulty as possible for you.
Schedule your test for early in the morning
You need to fast for at least 8 hours before the test. That means no eating or drinking anything except water. The hours you spend sleeping count toward this time.
What to eat before your fast
Before you start your fast, you can consume your usual diet. Experts recommend avoiding a very low carb diet for 2 to 3 days before a glucose test.
If your test is early in the morning, it should be easy to complete the fast. However, you still may have a few questions, particularly as it pertains to your morning routine.
Can I drink coffee or tea while fasting for a glucose test?
Even black coffee and green tea are off-limits, as caffeine may affect your fasting glucose levels. But recent research on black coffee suggests that the effect may be minor.
Still, coffee is a diuretic, meaning it can dehydrate you. This can make your veins smaller, which can make a blood draw more challenging.
It’s best to stick to just water.
Can I chew gum while fasting for a glucose test?
A 2020 study found that chewing gum — even sugar-free gum — doesn’t significantly affect glucose levels, but it can affect insulin levels. Study researchers still recommended that people avoid chewing gum before blood tests.
Can I smoke while fasting for a glucose test?
The nicotine in cigarettes can
Can you take insulin while fasting for a glucose test?
Yes, you can take your insulin as directed, even if you’re fasting. This includes both long-acting and short-acting insulin.
Can I take other medications while fasting for a glucose test?
You can usually take your other medications as prescribed before a fasting glucose test. But check with your doctor, as some medications may interfere with test results.
Summary: Things to avoid before a fasting glucose test
Remember to avoid the following in the 8 hours before your test:
- food
- beverages (including tea, coffee, and alcohol) except water
- chewing gum
- smoking
Your doctor may also advise you to avoid exercise for
The fasting glucose test is a single blood draw that usually lasts only a few minutes. You should get the results on the same day. Talk with your doctor about what the results mean and how you should interpret your blood glucose levels.