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What Impacts Blood Glucose Levels?

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Foods that contain carbohydrates will affect blood glucose levels the most. The foods that contain the most carbohydrate include those from the Fruit Group, the Starch and Starchy Vegetable Group, and the Milk and Yogurt Group. Foods with only carbohydrate may raise blood glucose more quickly than those that also contain fats and protein. Foods that are high in carbohydrate eaten with a meal that also contains fats and protein will have a slower impact on blood glucose than those eaten alone.

How quickly and how much blood glucose levels rise depends on:

Food composition

Blood glucose levels are affected differently depending on whether you eat foods containing carbohydrates, proteins, fats, or a combination of these three. Carbohydrates will cause blood glucose to rise the most and the most quickly. Liquids that contain carbohydrates (like milk and juice) will cause blood glucose to rise faster than solids that contain carbohydrates (like bread). Because of the impact that they have on blood glucose levels, carbohydrates are the most important macronutrient for people with diabetes to monitor.

Portion size

The amount of food that you eat also impacts blood glucose levels. Eating more food, or bigger portions, will cause your blood glucose levels to rise more than eating smaller portions. Since carbohydrates affect blood glucose levels the most, the amount of carbohydrate that you eat each day is very important in controlling your blood glucose levels. Talk to your health care provider or dietitian about how many grams of carbohydrates you should eat each day.

To find out how many grams of carbohydrates you are eating each day, it is important to be familiar with the food groups, serving sizes, and Nutrition Facts labels. As discussed in Food Groups and Diabetes, three food groups contain carbohydrate:

One serving from each of these groups contains about 15 grams of carbohydrates. Therefore, eating one serving from any of these three groups will impact your blood glucose level in about the same way. For examples of one serving from these three groups see Food Groups and Diabetes.

nutrition facts label
Carbohydrate = Fiber + Sugar + Starch

Another way to find out how many grams of carbohydrates are in a particular amount of food is to read the Nutrition Facts label on the back of a product. This is a picture of the Nutrition Facts label found on almost all foods sold in this country. Look at the portion on the label that tells how much “Total Carbohydrate” is in the food in order to decide how much it might raise your blood glucose. As you can see, this product has 41 grams of total carbohydrates per serving.

For comparison, one slice of bread (one serving from the Starchy and Starchy Vegetables Group) has about 15 grams of carbohydrate. Since our bodies change almost all of the carbohydrates we eat into blood glucose, be sure to look at “Total Carbohydrate” and not just at “Sugars” to see how much a food will raise your blood glucose. "Total Carbohydrate" will be greater than the sum of the listed “sugars” and “fiber” because starches are also counted in total carbohydrates. For some very high fiber foods that have 5 or more grams of fiber per serving, net carbohydrates may be used instead of total carbohydrates. Net carbohydrate is just total carbohydrate in a serving of food minus the grams of fiber. Net carbohydrates are used when considering very high fiber foods, because the body cannot digest carbohydrates from fiber and therefore they do not raise blood glucose levels.


Blood glucose levels are affected by the timing of meals and snacks. Eating three meals and possibly one or two snacks at the same time every day will help keep your blood glucose levels more consistent. Ask your doctor or dietitian how many meals and snacks you should eat each day.

Blood glucose levels are affected by the timing of meals and snacks
Blood glucose levels are affected by the timing of meals and snacks.

It is also important to eat about the same amount of carbohydrate at each meal or snack to keep your blood glucose levels within target range, or to have your medication match your carbohydrate intake. Below is a graph of blood glucose levels from a person without diabetes who has eaten 3 meals and two snacks in one day. At each meal this person ate about the same amount of carbohydrate. As you can see, this person’s blood glucose level rose and fell in about the same way after every meal or snack. In someone who does not have diabetes, insulin secretion will automatically adjust to match the amount of carbohydrate that they eat.

However, those who have diabetes do not react the same way. Since people with diabetes have difficulty regulating their blood glucose levels, they should eat the amount of carbohydrate recommended by their doctor, and space this carbohydrate evenly throughout the day. This will help keep blood glucose levels in their target range.

Back to: Eating for Target Blood Glucose Levels

This document is a source of information only, and is not medical advice.