You may be surprised to learn that checking your blood sugar after you eat can be more important than checking before you eat a meal. If you are like most people, you just check your blood sugar in the morning when you get up. Although that reading is important, you may be missing a helpful source of information.
Why check after meals?
After-meal readings tell you about the impact of food on your blood sugar. The blood sugar reading taken two hours after you start to eat should be about 30 mg/dl higher than before you ate. So if your blood sugar was 117 mg/dl before you ate two cups of pasta with chicken and vegetables and 322 mg/dl two hours later, you’ve learned that two cups of pasta is too much for you. However, a reading of 157 mg/dl two hours after eating one cup of pasta helps you to learn the portion of pasta that your body can handle.
Many people are shocked by the elevated 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. But, finding 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 Equal or Sweet ‘N Low may only raise your blood sugar to 150 mg/dl. Blood glucose rises after eating mainly from the carbohydrates you eat. Carbohydrates begin to raise blood glucose within 15 minutes of food intake and is changed to nearly 100% glucose within about two hours. Blood glucose levels should be back to your pre-meal target by about 3 to 4 hours after the start of meals.
In general, 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 carbohydrates.
For example: after observing varying after breakfast blood glucose levels, you realize the bagel you eat raises your blood glucose higher than the oatmeal. Then you read the “Nutrition Facts” labels and learn that a bagel contains 60 grams of carbohydrate and oatmeal contains 30 grams.
- Learn the effects of different foods on your blood glucose.
Perhaps you choose to eat a high fiber meal, or maybe a few slices of pizza, a glass of wine or a dessert? These choices can all affect your blood glucose differently.
- 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.
Once people learn the importance of checking their blood sugar two hours after a meal, they are free to experiment with different foods. Portions of ethnic foods or combination foods such as casseroles are often hard to measure. Checking your blood sugar two hours after you eat is the only way to know the portion of ethnic foods or combination foods that your body can tolerate.
This essential feedback puts you in the driver’s seat when making food choices. You may have intended to check your blood sugar after you ate but forgot because you were involved with something. Simply forgetting is the biggest barrier to measuring blood sugar after meals. Some people set a timer or a wrist watch alarm as a reminder. Don’t be discouraged if you forget, just try another time.
Do I have to check more often?
Blood sugar monitoring is meant to provide you (and your health care provider) with helpful feedback. Just writing numbers in a log book is meaningless. You may choose to check three times per week and 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 cereal so that day you will check before and after breakfast. An elevated reading before a meal has nowhere to go but up. If your blood sugar is high before a meal, it will only be higher after a meal so you won’t learn anything about the impact of the food you ate on your blood sugar. Pre-meal readings help you and your health care provider evaluate your medications and overall eating patterns.
What else do the numbers mean?
The readings taken two hours after a meal also tell you about the amount of insulin that your body is making. If your pre-meal reading is within range and the reading two hours later is high but you didn’t overeat, the after-meal reading can give us a clue about the amount of insulin made by your pancreas. In type 2 diabetes, the body loses its ability to immediately release insulin after food is eaten.
An elevated blood sugar reading two hours after a healthy meal may be telling us that your body needs a boost of insulin right after you eat. There are some new medications that provide a boost of insulin after a meal. Either Prandin (repaglinide) or Starlix (nateglinide) can lower your blood sugar after meals. Those who take rapid-acting or fast-acting insulin before a meal use the pre-meal reading to decide what dose of insulin to inject and they use the after-meal reading to evaluate if the dose was correct.
What do experts say?
A group of experts recently reviewed the role and importance of after-meal blood glucose levels in diabetes control. The experts did not set an after-meal target, nor did they conclude that everyone with diabetes should check it. However, by the time they got done listing who would benefit from after-meal checking, it included many people. They suggest checking if you:
- suspect you have high blood glucose levels after meals and/or
- take a diabetes medication intended to lower after-meal blood glucose levels and/or
- need to monitor for low blood glucose levels or
- have diabetes during pregnancy (gestational).