You may have a lot of questions if your doctor asks you to take a glucose test. One of the top questions is: “What can I eat beforehand?” 

This can depend on many factors, including why you’re being asked to take a glucose test and what kind of glucose test you’re getting. 

This article will explain what to eat (or not eat!) before a glucose test. 

A person holds a fork and knife over an empty plate

Why would I need a glucose test? 

Typically, people require a glucose test because they are at an increased risk for diabetes or because a physician thinks their patient may have diabetes. 

Any of the following reasons may apply:

  • Being overweight or obese
  • Being sedentary 
  • Having a family history of diabetes (any type)
  • Being over the age of 45 and in a high-risk group 
  • Being pregnant (getting tested for gestational diabetes between 24-28 weeks gestation is normal) 
  • Having symptoms of diabetes, including weight loss, frequent urination, extreme thirst, and fruity-smelling breath 

What are the different kinds of glucose tests available?

What you can and can’t eat before a glucose test will depend on which kind you get. 

There are four kinds of glucose tests:

Fasting glucose test

A fasting glucose test is used to diagnose diabetes and measures the amount of sugar (or glucose) in your bloodstream after a period of not eating. 

  • Blood sugar levels under 99 mg/dL are considered non-diabetic. 
  • Blood sugar levels between 100-125 mg/dL are considered prediabetic
  • Anything 126 mg/dL or above is considered diabetic.

A fasting glucose test, however, will not tell you which kind of diabetes you may have. 

You cannot eat anything before a fasting glucose test, or it defeats the purpose of the “fast.” 

You may sip small amounts of water between 8-12 hours before the test.  It is easiest if you schedule this test early in the morning so that you can eat breakfast immediately afterward. 

Hemoglobin A1c test 

A hemoglobin A1c test, or an HbA1c test for short, measures your average blood glucose level over the previous three months. 

It is recommended for anyone over the age of 45 and anyone with additional risk factors for diabetes. 

  • An HbA1c of under 5.7% is considered non-diabetic. 
  • A result between 5.7-6.4% suggests prediabetes. 
  • Anything over 6.5% suggests diabetes.

However, these tests do not diagnose specific types of diabetes. Additionally, if someone’s HbA1c levels come back high, a doctor will usually confirm with a finger stick blood glucose test.

HbA1c tests do not require patients to fast, and eating before a test will not skew results. 

You can take an A1c test at your doctor’s office or use a home A1c test.

Glucose tolerance test 

Pregnant people are usually tested for gestational diabetes, unless they already have a diabetes diagnosis at conception. 

This type of glucose test is called a glucose tolerance test, and it’s given to pregnant people between 24-28 weeks of gestation. 

A glucose tolerance test measures blood sugar before and after you drink a sweet liquid that contains between 50-100 grams of fast-acting sugar. 

Blood sugars are checked one hour, two hours, and sometimes even three hours after drinking the sweet drink. 

At two hours, a blood sugar of 140 mg/dL or lower is considered normal.

140-199 mg/dL indicates prediabetes

200 mg/dL and above may indicate gestational diabetes and require intervention. Sometimes this means insulin, sometimes not.  

A glucose tolerance test requires the patient to fast. This means no food or drink (besides water) 8-14 hours before the test. 

It’s best to schedule this test in the morning so you can eat breakfast afterward. 

At-home glucose testing 

Many people routinely test their blood sugars from the comfort of their own homes, whether or not they currently live with diabetes. 

Buying a glucose meter and test strips at a local pharmacy is easier than ever. Plus, you do not need to fast to test your blood sugar properly. 

  • A non-fasting blood glucose of less than 140 mg/dL is considered non-diabetic.
  • Blood sugar levels between 140-199 mg/dL indicate prediabetes.
  • Anything over 200 mg/dL non-fasting indicates diabetes. 

Unlike a fasting glucose test that has lower thresholds for prediabetes and diabetes, a non-fasting test doesn’t require the patient to avoid foods or drinks beforehand. The diagnostic criteria are higher as a result. 

So, what can I eat before a glucose test?

First, check with your doctor to be sure that the test you’ll be taking doesn’t require you to fast. Testing protocols and your individual situation may change their recommendations for you.

If you’ve been approved to eat before a glucose test, it’s helpful to make sure you’re loading up on plenty of fresh produce. 

This includes fruits and vegetables, along with filling fiber and low-fat protein. Boost your grocery list with ingredients like fish, chicken, and turkey. 

Add low-fat dairy options to your diet like Greek yogurt and mozzarella cheese. Healthy fats, like extra virgin olive oil, peanut butter, and eggs are also great choices. 

As always, drink plenty of water and stay hydrated. 

What foods should I avoid before a glucose test?

Here’s a list of foods you should avoid before taking a glucose test: 

  • Overly processed foods
  • Refined carbohydrates
  • Food with added sugar: soda, cakes, candy, cookies, and ice cream
  • Limit caffeine and alcohol, especially sugary mixed drinks 

What if the glucose test says I have diabetes or prediabetes? 

If your blood sugar falls outside the normal range on a blood glucose test, your doctor will typically order a re-do. This is to make sure that the results weren’t an outlier. 

Call your doctor if your at-home glucose meter reports high blood sugar. They will order a fasting glucose test taken at a laboratory, an HbA1c test, or ideally both. 

If your blood sugar levels are higher on an HbA1c test, your doctor will almost always order a fasting glucose test to see where your blood sugars are in real-time. 

They may even refer you for a continuous glucose monitor (CGM) system to track your blood sugars consistently for a few days. The CGM will pick up on any trends or blood sugar spikes that a fingerstick test may miss.

If your glucose tolerance test comes back high while pregnant, the test is usually repeated before making a gestational diabetes diagnosis. 


While there is no particular food to eat before a glucose test, knowing what kind of test you’re having is helpful for you to determine if you can even eat anything at all!

Remember, fasting glucose tests and oral glucose tolerance tests for pregnant people require fasting, and you can only drink a few sips of water for several hours beforehand. 

HbA1c tests and at-home glucose monitoring, however, do not require any fasting. 

If you want to prep for an HbA1c test or an at-home glucose test, it’s helpful to load up on all-natural, whole foods, drink plenty of water, and eat foods with fiber, fat, and protein. Avoid added sugars, refined carbohydrates, and processed foods. 

Connect with your doctor before your glucose test. They can offer food suggestions or let you know if you need to fast—testing protocols can vary by patient.