When you need a blood test that requires fasting, you’ll want to be aware of things that could cause faulty test results. Drinking diet soda with artificial sweetener before a fasting blood test might skew your results. That’s a risk to avoid, whether your tests are routine or for a certain health condition.
Why Is Fasting Important?
No one likes to have to go without food for an extended period of time, so hopefully your doctor will request it only when it’s necessary. You need to fast before some types of blood tests because nutrients from food and drinks that you consume enter your bloodstream. These nutrients may falsely alter levels of the specific substance your test is designed to measure.
For example, according to Harvard Health Publishing, doctors use a blood sugar test to detect diabetes and to monitor the effectiveness of treatments for people who have diabetes. After your body converts food into sugar, also called glucose, the glucose enters your bloodstream. If you eat too close to the test, your glucose level could falsely appear to be too high. This is also similar for blood fats called triglycerides, which also require a fasting blood test to measure. That’s because their levels remain elevated after a meal.
Diet Soda and Fasting
With some fasting tests, you can still drink unsweetened coffee and tea, because these don’t affect blood sugar. It’s important to ask your doctor about what you can and can’t have before your specific blood test.
Regardless of whether you can have plain coffee and tea, you shouldn’t drink diet sodas with artificial sweeteners before a blood test, because they can affect your results. The ingredients in these beverages vary widely, as do their effects on blood sugar.
It’s possible for artificial sweeteners to affect blood sugar levels, according to a review published in the journal Frontiers in Nutrition.
Some sugar alcohols provide carbohydrates that will affect blood sugar, including:
- Isomalt
- Lactitol
- Maltitol
- Mannitol
- Sorbitol
- Xylitol
Diet sodas may also contain other ingredients that can affect your blood sugar. If your doctor’s guidance only allows for water and unsweetened tea and coffee before your blood test, it's a good idea to follow these orders. That way, your test results will be as accurate as possible.
Other Testing Precautions
If you make a mistake and drink a diet soda during the time you’re supposed to be fasting, give your doctor's office a call. Your doctor may recommend rescheduling the test just to be on the safe side.
According to MedlinePlus, there are a few other things to avoid doing in the 8 to 12 hours before a fasting blood test:
- Exercising
- Chewing gum
- Smoking
In general, fasting blood tests are scheduled for first thing in the morning. This usually means you have dinner the night before and then skip breakfast the morning of your test. If you smoke, don’t light up during this period. If you’re a morning exerciser, skip your workout on the day of your test. And hold off on the gum chewing until afterward. You can resume your regular habits right after the test.
You’ll likely be hungry, so bring a snack with you to your appointment. You can have it after your blood test. Rather than grabbing a sugary coffee drink or sugar-laden granola bar on the way to work, pack a snack that has complex carbohydrates that digest and absorb slowly into your bloodstream. Some healthy, energy-boosting ideas are:
- An apple and some nut butter
- Hummus and carrot sticks
- Oatmeal with fresh berries
- Hard-boiled eggs with whole-grain bread
