Why is blood sugar so important after eating?

Postprandial blood sugar. Few of those with diabetes know why it is so important...

Blood sugar after a meal is referred to as postprandial blood sugar. So the opposite, namely before a meal, is called preprandial. The American Diabetes Association (ADA) advises keeping your blood sugar levels before meals between 80–130 mg/dl and your levels 1–2 hours after meals under 180.

Usually, blood sugar begins to rise 10-15 minutes after a meal and reaches its peak after an hour. However, it is important to note that these are just approximate guidelines as postprandial glucose depends on several factors, such as the type of food consumed.

Influence on HbA1c

Research has shown that postprandial blood sugar levels are significant for HbA1c. Even if glucose spikes after eating are only brief, they still have the potential to raise HbA1c over the course of the day. Most people with diabetes check their blood sugar before a meal but not afterwards or they leave it until the next mealtime. This can lead to glucose spikes being undetected and remaining high for a long period of time.

How to deal with high postprandial blood sugar levels

Be sure to check your levels at least 90 minutes after a meal. Why? By that time rapid acting analogue insulin has reached its maximum effect (as opposed to normal insulin that not only takes longer to have an effect but also acts longer).

A useful tip is to set a reminder for a specific time and you’ll automatically be reminded to test your blood sugar levels. If you have type 1 diabetes, your blood sugar should be between 5 and 9 mmol/litre at least 90 minutes after eating (NICE Guidance for type 1 diabetes in adults, 2016). Of course your doctor may recommend another postprandial level according to your personal needs and state of health.

If it’s still too high then you should look into the causes such as:

  • what type of food did I eat?

  • did I correctly estimate my carbs?

  • is my insulin-to-carb ratio correct?

  • and is the injection-meal interval correct?

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