Can you drink coffee while fasting for blood work?

In this article, we will provide the answer to the question: “Can you drink coffee while fasting for blood work?”. In addition, we will discuss whether you can drink coffee before a cholesterol blood test and the effects of coffee on your blood.

Can you drink coffee while fasting for blood work?

No, you can not drink coffee before a blood work. Unlike water, drinking coffee can interfere with the results of certain tests. Therefore, its consumption should be avoided, whether pure, with sugar or with sweetener.

Even without the addition of sugar, coffee can interfere with the results of certain tests, changing some biochemical dosages.

Can you drink coffee before a cholesterol blood test?

No, you can’t have coffee, even sugar-free, before a cholesterol blood test. Any food, with the exception of water, when ingested, interferes with the test results because they modify some biochemical dosages.

This is because normally 1 hour after we wake up, our body experiences a spike in cortisol, which is also responsible for keeping us awake and alert.

The caffeine present in this drink causes the level of this hormone to rise in the body, in addition to being boosted in the increase of Adrenaline, Noradrenaline and GH, especially in stressful situations.

These and other changes can “make up” the results of your exams, therefore, it is not recommended to consume coffee during the fasting period, when it is necessary!

What are the effects of coffee on your blood?

The main effect of coffee on your bloodstream is the fluctuation of insulin with coffee consumption. Coffee consumption causes insulin sensitivity to go down and up, according to the amount of caffeine ingested.

A study published in “Diabetes Care” in December 2004 found that high coffee consumption was associated with higher concentrations of fasting insulin levels.

Insulin is a hormone secreted by the pancreas that is used to process blood glucose. High levels of this hormone indicate greater resistance to its effects. 

This means that people who consume significant amounts of coffee regularly may have increased concentrations of glucose in their blood. More research is needed to reveal the implications of this effect.

What can I eat before having a blood test?

The food or fasting required will depend on the type of blood test. The healthcare provider ordering the test will tell you if you will need any special preparation.

In some blood tests you will be allowed to eat normally, while in others where fasting is required, you will be warned in advance not to eat or drink anything other than water.

The truth is that any food, if consumed in excess in the days before the exam, will cause you to have a higher level of certain substances in the body, which can interfere with the results.

For example, if you eat a lot of potassium-rich foods, such as bananas or sweet potatoes, the test will indicate more potassium in your blood.

What is the required fasting time?

For blood tests, the minimum fast is 3 hours and should never go beyond 14 – since at this time the body starts to use reserves, burning fat and protein, which may alter the final result of the tests. It turns out that each person has a different metabolism and today that 12-hour time is not always necessary. 

Therefore, generally speaking, you can have breakfast if your exam is at least 3 hours after your meal. For example, breakfast at 7:00 am with an exam at 10:30 am is allowed.

But it’s worth paying attention to confirm with your doctor and your laboratory the necessary fasting time for you. There may be other tests along with the blood test and you don’t know it.

Finally, before any exam, avoid intense physical activity for at least 24 hours and no alcoholic beverages for at least 72 hours (3 days).

Which blood tests require fasting?

Blood glucose, cholesterol, and triglycerides are the most common tests to ask for fasting, as food intake affects these tests. A 12-hour fast is also required when performing the iron analysis test to diagnose anemia. Sometimes your doctor may ask you not to drink alcohol or to avoid taking supplements before blood tests.

Is fasting necessary to donate blood?

It is not necessary to fast to donate blood. You cannot donate on an empty stomach. If you donate in the morning, eat breakfast normally, you can drink juice, coffee, tea, milk (preferably skim or soy milk) and eat bread and fruits (except avocado and jackfruit) normally. It is good to avoid fatty foods, such as: fried foods, snacks, butter, eggs and others.

If you donate in the afternoon, the ideal is to do it two hours after lunch (watch the digestion period). Lunch normally, preferably with grilled meats, salads, rice, beans. Avoid eating fatty foods (fried foods, eggs, pasta, mayonnaise, ice cream, chocolates, etc.).


In this article, we provided the answer to the question: “Can you drink coffee while fasting for blood work?”. In addition, we discussed whether you can drink coffee before a cholesterol blood test and the effects of coffee on your blood.


Hi, I am Charlotte, I love cooking and in my previous life, I was a chef. I bring some of my experience to the recipes on this hub and answer your food questions.