Why Do We Have to Eat When Taking Insulin?

Insulin is a medication your physician prescribes when you have diabetes. Diabetes affects your body’s ability to produce insulin, a hormone that helps your body use the sugars in your food for energy. You typically inject the insulin into your body to deliver it into your bloodstream prior to eating a meal. However, different types of insulin work at varying rates, depending upon the type your doctor prescribes. Knowing how each works helps you to understand why you take insulin prior to eating.

Blood Glucose

Balancing your blood glucose level is the purpose for taking insulin. When you have diabetes, you are constantly checking your blood sugar levels to ensure they do not go too high or low. While your desired blood sugar levels may vary based on your age and health, general recommendations are to have a level between 70 and 130 mg/dL before a meal and less than 180 mg/dL between one and two hours after you begin to eat your meal. Eating food raises your blood glucose level while administering insulin lowers your blood sugar level.

Insulin and Your Food

When you take insulin, your body uses it to allow glucose -- sugar from your blood -- into your cells. Timing is important when taking insulin because you want it to work at or around the same time you eat. Taking insulin after your meal could cause your blood sugar level to spike before your insulin kicks in. If your blood sugar levels are too high, this increases your risk for conditions like heart disease, heart attack and stroke.

Insulin Types

The time you use insulin before a meal depends upon the type of insulin you use 3. Fast-acting insulin medications can begin working as quickly as 10 to 15 minutes after injecting them. The insulin continues working for an hour or longer to regulate your blood glucose level. Moderate- and long-acting insulins take longer to begin working -- typically about two to four hours. However, these insulin types work longer, sometimes up to 24 hours. The type your physician prescribes depends upon your daily schedule and overall health. You may choose fast-acting insulin if you do not eat at regular intervals and have a difficult time predicting when you will be eating.


Just as not giving yourself insulin soon enough can cause you to experience high blood sugar levels, injecting too much insulin can make your levels dip too low. Talk to your physician about carefully monitoring your insulin levels and signs your insulin may be dipping too low. Maintaining careful blood glucose control is vital to staying healthy with diabetes.