Checking Your Blood Glucose After You Eat

Reviewed and updated by Di Bush, PhD

Perhaps you are like most people who just check your blood sugar in the morning when you get up. Although that reading is needed, you may not realize that checking your blood sugar after eating can be more crucial than checking it before eating.

Why check after meals?

After-meal readings tell you about the impact of foods to your blood sugar. The blood sugar reading taken two hours after you start eating should only be about 30 mg/dl higher compared to the reading before you ate. So if your blood sugar was 117 mg/dl before you ate two cups of pasta with chicken and vegetables and became 322 mg/dl two hours later, it means that the two cups of pasta is too much for you. However, if the reading resulted to 157 mg/dl two hours after eating one cup of pasta, it means that the portion of pasta is just enough for your body to handle.

Many people are shocked by the readings that they measure after meals. For example, you may decide to drink sweetened soda with your meals because your fasting blood sugar was always less than 120 mg/dl. When you get measured readings over 400 mg/dl after drinking sweetened soda, you may decide to switch to sugar-free soda. Checking after-meals can also teach you about better food choices or products.

Eight ounces of orange juice with your breakfast may raise your blood sugar to 299 mg/dl two hours later, whereas 8 ounces of a fruit drink sweetened with sugar substitute may only raise your blood sugar to 150 mg/dl. Blood glucose rises after eating mainly from the carbs you eat. Carbs begin to raise blood glucose within 15 minutes of food intake and are changed to nearly 100% glucose for about two hours. Blood glucose levels should return to your pre-meal target by about 3 to 4 hours after the start of meals.

People spend about half of each day in a state where blood glucose is higher than pre-meal levels. If your blood glucose levels after meals are often high, it will be hard for you to achieve good control.

What can you learn?

  • Learn if you are eating either too much or uneven amounts of carbs.
  •  Learn the effects of different foods on your blood glucose.
  • Learn the effect of activity on your blood glucose. Is your blood glucose lower if you take a walk after dinner?
  • Learn if the diabetes medicine you take to lower after-meal blood glucose is working effectively or not.

This feedback puts you in the driver’s seat when making food choices. Therefore, if you are prone to forget to check your blood sugar after you eat, then set a timer or a wrist watch alarm to remind you since being in control of your blood sugar can put you in more control of your daily life.

Do I have to check more often?

Checking your blood sugar is meant to provide you and your healthcare team with helpful feedback. Just writing numbers in a log book means nothing, so you should try to choose to check a certain number of times a week. Alter the times based on your needs so if you want to learn the impact of two slices of pizza on your blood sugar at lunchtime, check before and two hours after lunch that day.

Two days later, you may decide to try a new breakfast food, so that day you will check before and after breakfast. A high reading before a meal has nowhere to go but up, so if your blood sugar is high before a meal, it is best to wait until later to check your blood glucose level. You will not learn about the impact a food had on your blood sugar if it is high pre-meal. Pre-meal readings help you and your healthcare team check to see if your medications or lifestyle patterns need to be changed to reach target goals for your blood sugar levels.

What else can post-meal numbers show?

The readings taken two hours after a meal also tell you about the amount of insulin your body makes. If your blood sugar level increases two hours after eating your meal, and you did not overeat, that means your pancreas may not be making enough insulin as in Type 1 diabetes. This may reveal that your body needs a boost of insulin. There are some new medications that provide a boost of insulin after a meal that include Prandin (repaglinide) or Starlix (nateglinide). Your health care team can help you decide if such a boost would help you.

What do experts say?

A group of experts reviewed the role of post-meal blood glucose levels in diabetes control and suggest checking if you:

  • suspect you have high blood glucose levels after meals
  • take a diabetes medication meant to lower post-meal blood glucose levels
  • need to monitor for low blood glucose levels
  • have diabetes while pregnant

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