What to eat before a glucose test

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

This may depend on a number of factors, including why you are being asked to take a glucose test and what type of glucose test you are getting.

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

Why would I need a glucose test?

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

Any of the following reasons may apply:

Overweight or obese
Sedentary lifestyle
Having a family history of diabetes (any type)
Being over the age of 45 and in a high-risk group
Being pregnant (testing for gestational diabetes between 24 and 28 weeks of pregnancy is normal)
Diabetes symptoms including weight loss, frequent urination, extreme thirst, and fruity breath odor


What are the different types of glucose tests available?
What you can and cannot eat before your glucose test will depend on what type you get. 
There are four types of glucose tests:
Fasting glucose test
The fasting glucose test is used to diagnose diabetes and measures the amount of sugar (or glucose) in the blood after a period of fasting. 

A blood sugar level below 99 mg/dL is considered non-diabetic. 
A blood sugar level between 100-125 mg/dL is considered pre-diabetes. 
Anything 126 mg/dL or higher is considered diabetes.

However, a fasting glucose test will not tell you what type of diabetes you may have. 
You can’t eat anything before the fasting glucose test or it defeats the purpose of “fasting”. 
You can drink a small amount of water 8-12 hours before the test.  It’s easiest to schedule this test early in the morning to eat breakfast right after. 
Hemoglobin A1c test 
The hemoglobin A1c test, or HbA1c test for short, measures the average blood glucose level over the past three months. 
It is recommended for people over 45 and for people with additional risk factors for diabetes. 

An HbA1c below 5.7% is considered non-diabetic. 
A score between 5.7-6.4% suggests pre-diabetes. 
Anything above 6.5% suggests diabetes.

However, these tests do not diagnose specific types of diabetes.  Additionally, if someone’s HbA1c level returns to high levels, the doctor will usually confirm this with a fingerstick blood glucose test.
HbA1c tests do not require patients to fast, and eating before the test will not distort the results. 
You can get an A1c test at your doctor’s office or you can do an A1c test at home.

Glucose tolerance test 
Pregnant people are usually screened for gestational diabetes unless they are already diagnosed with diabetes at the time of conception. 
This type of glucose test is called a glucose tolerance test and is given to pregnant women between 24 and 28 weeks of pregnancy. 
The glucose tolerance test measures blood sugar levels before and after drinking a sugary liquid containing 50 to 100 grams of fast-acting sugar. 
Blood sugar levels are checked an hour, two hours and sometimes even three hours after drinking a sugary drink. 
After two hours, a blood sugar level of 140 mg/dL or less is considered normal. 
140-199 mg/dL indicates pre-diabetes. 
200 mg/dL and above may indicate gestational diabetes and require intervention.  Sometimes that means insulin, sometimes not.  
The glucose tolerance test requires the patient to fast.  This means no food or drink (except water) for 8-14 hours before the test. 
It’s best to schedule this test in the morning so you can have breakfast later. 

Home glucose test 
Many people routinely test their blood sugar levels in the comfort of their own home, whether they currently have diabetes or not. 
Buying your meter and test strips from your local pharmacy is easier than ever.  In addition, you do not need to fast to properly test your blood sugar. 

A non-fasting blood glucose level of less than 140 mg/dL is considered non-diabetic. 
A blood sugar level between 140-199 mg/dL indicates pre-diabetes. 
Anything above 200 mg/dL without fasting indicates diabetes. 

Unlike the fasting glucose test, which has lower thresholds for prediabetes and diabetes, the non-fasting test does not require the patient to avoid foods or drinks beforehand.  As a result, the diagnostic criteria are higher. 
So what can I eat before a glucose test?
Check with your doctor first to make sure the test you’re going to be doing doesn’t require fasting.  Test protocols and your individual situation may change their recommendations for you.
If you’ve been approved to eat before your glucose test, it’s a good idea to make sure you’re loading up on plenty of fresh produce. 
This includes fruits and vegetables as well as filler fiber and low-fat protein.  Enrich your shopping list with ingredients like fish, chicken and turkey. 
Add low-fat dairy products like Greek yogurt and mozzarella cheese to your diet.  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 is a list of foods to avoid before taking a glucose test: 

Too processed food
Refined carbohydrates
Foods with added sugar: soda, cakes, sweets, cookies and ice cream
Limit caffeine and alcohol, especially sweet mixed drinks 

What if my glucose test shows I have diabetes or pre-diabetes? 
If your blood sugar falls outside the normal range on a blood glucose test, your doctor will usually order you to repeat it.  This is to ensure that the results were not outliers. 
Call your doctor if your home glucometer reports high blood sugar.  They will order a laboratory fasting glucose test, an HbA1c test, or preferably both. 
If your blood sugar is higher on the HbA1c test, your doctor will almost always order a fasting glucose test to see where your blood sugar levels are in real time. 
They may even refer you to a continuous glucose monitoring (CGM) system to track your blood sugar consistently over several days.  The CGM will detect any trends or spikes in blood sugar that may be missed by the fingertip test.
If the glucose tolerance test result is high during pregnancy, the test is usually repeated before a diagnosis of gestational diabetes is made. 

Application
While there’s no specific food to eat before a glucose test, knowing what type of test you’re taking is helpful in figuring out if you can eat anything at all!
Remember that fasting glucose tests and oral glucose tolerance tests for pregnant women require fasting, and you can only drink a few sips of water a few hours before. 
However, HbA1c testing and home blood glucose monitoring do not require fasting. 
If you want to prepare for an HbA1c or glucose test at home, 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. 
Check with your doctor before taking a glucose test.  They can offer nutritional suggestions or let you know if you need to fast – testing protocols may vary from patient to patient.