By Michael Ormsbee, Ph.D., Florida State University

Edited by Kate Findley, The Great Courses Daily

Do you feel irritable when you’re hungry or want to take a nap after a sugary or carb-heavy meal? Dr. Ormsbee discusses the pros and cons of using the glycemic index of foods to maintain steady blood sugar levels, and offers alternatives.

Blood Glucose Levels and Mood

The glucose in your blood is used by cells to produce energy, especially by your nervous system and red blood cells. However, there is a limit to how much glucose the body can use, and when those uses are met, the body stores the energy in other forms such as fat. Our bodies work best for us when blood glucose levels remain constant, without large fluctuations throughout the day.

To a large extent, blood glucose levels can determine our mood and our energy levels. Just think about the last time you were really hungry. You probably found yourself irritable, angry, and moody. 

Much of this mood change occurs when your blood glucose dips too low or gets too high. After an overnight fast, we are able to maintain our blood glucose values using glycogenolysis, or the breakdown of glycogen to make glucose, and gluconeogenesis, the creation of new glucose from non-carbohydrate sources in the liver.

Glycogenolysis provides about 65 percent to 75 percent of the glucose released into your blood, and gluconeogenesis provides the remaining 25 percent to 35 percent of the glucose released by the liver. Once you store glucose as muscle glycogen, it cannot be converted back into blood glucose—it is in essence locked in your cells and must be used for energy. 

How Food Impacts Blood Sugar

Only liver glycogen can help maintain your blood glucose concentrations, not muscle glycogen, and some carbohydrate foods can have a dramatic impact on how high your blood glucose will rise after a meal. Some foods only have a minor effect on blood glucose, which, naturally, your body would prefer as it likes things to stay constant.

When blood sugar is elevated for a prolonged period, numerous detrimental health and body composition outcomes can occur. The good thing is that we have an index that can tell us how quickly a food you eat will raise your blood glucose levels: the glycemic index.

The glycemic index gives us an idea of how quickly 50 grams of a specific food can raise your blood glucose levels compared to 50 grams of table sugar, which is given a glycemic index value of 100. By knowing the glycemic index of common foods that you eat, you will have an idea of what your blood glucose response will be after you eat that food. 

The higher your blood glucose, the higher the hormone insulin is in your blood. The hormone is highly involved with the storage of carbohydrates into your cells. 

Insulin also blunts fat burning in most cases. It plays a critical role in this important function of balancing blood glucose levels.

If you have high insulin levels for a prolonged period, losing fat will likely be much more difficult. High levels of insulin also may interfere with your ability to achieve optimal health. 

Not surprisingly, foods like breads, pastries, and bagels have a high glycemic index and therefore spike your blood sugar. On the other hand, foods like apples, cherries, beans, and nuts tend to have a much lower glycemic index. Many nutrition experts recommend eating foods that primarily have a low glycemic index value.

Issues with Glycemic Index

However, if you based your entire diet on the glycemic index, that isn’t optimal either. This is because: one, you don’t consistently eat 50 grams of a particular food, which is what the glycemic index is based on; and two, you typically don’t eat just one nutrient at a time—you would eat a meal of mixed carbohydrate, fat, and protein. 

Therefore, if you had a high glycemic index food such as a handful of pretzels, this wouldn’t cause much of a problem if you combined them with lower glycemic foods like a serving of vegetables and a lean protein.

How you prepare foods in the kitchen can influence the glycemic index of the food as well. For example, simply boiling carrots will raise their glycemic index. 

It is also important to recall that the glycemic index of a food doesn’t tell you much about the quality of that food. For example, the American Diabetes Association stresses that many nutritious foods have a higher glycemic index than foods that we typically think of as junk food. 

Candy bars fall into this category. They have a similar glycemic index value to green peas. However, you probably wouldn’t eat the same serving size in the weight of peas as easily as you would from a candy bar. 

It’s quite easy to eat 50 grams of some foods, but rather hard to eat 50 grams of others, like celery. Thus, the glycemic index provides a snapshot of good information but needs to be balanced with other basic nutrition principles.

Alternatives to Glycemic Index

One of the mechanisms that has been developed to overcome some of the shortcomings of the glycemic index is called the glycemic load. The glycemic load is the glycemic index of a particular food multiplied by the actual amount of food that you eat. Similar to a high glycemic index, a high glycemic load of a carbohydrate food means that your blood glucose values will increase quickly.

This glucose response is used to predict what should happen to insulin levels. The trouble is there is not always a direct correlation between a high glycemic index or glycemic load food with a high insulin response.

For this reason, research from the American Journal of Clinical Nutrition has provided an insulin index of common foods. Thus, rather than eating and measuring how high your glucose gets in your blood, we would measure how high insulin gets in response to specific foods.

This article was edited by Kate Findley, Writer for The Great Courses Daily.