Why Is the Potato Glycemic Index Higher Than Table Sugar?

Did you know the potato glycemic index (GI) score—a measurement of how much foods raise your blood glucose—is high? Each potato variety has a different index score, but many fall between 80 and 90.

Potatoes are a staple in diets globally because they are an affordable and nutritious vegetable. People who limit high-glucose foods wouldn't naturally avoid potatoes because we often associate high-GI foods with those containing sugar.

So how is it that potatoes have a high GI score? It's all about starch and how it converts to glucose in your body. Let's dive in to learn more about the potato glycemic index.

The Starch Effect

Too often, glucose is associated with sweetness. Regular white potatoes are not a food considered sweet or sugary. However, potatoes are almost all starch made of long strings of glucose.

Since the starch in potatoes is rapidly digested, the potato glycemic index can be almost as high as that of glucose alone. The glycemic index of glucose is 100 points; potatoes are usually listed as being in the high 80s or low 90s.

How is that possible? Sucrose (table sugar) has a GI of 59. It is a disaccharide (two sugar) molecule made up of one glucose molecule and one fructose molecule. Fructose is processed differently in your body than glucose, and it doesn't affect your blood sugar as much.

An ounce of carbohydrate from potatoes has twice as much glucose as sugar. When you think of it that way, it's only logical that potatoes would raise blood glucose more significantly than table sugar.

However, not all potatoes are created equal, and there are ways to lower their impact on blood glucose. You can still enjoy a few potatoes here and there; keep your servings in check.

Factors to Consider

Two primary factors influencing the potato glycemic index include the variety and cooking method.

Varieties of Potatoes

There are many varieties of potatoes and it would not be accurate to say that every potato has a glycemic index of 80 or 90. In fact, researchers have found that some varieties of potatoes can be as low as 53 on the glycemic index.

In one study, researchers tested seven potato varieties: Russet Burbank, Mayflower, Nicola, Bintje, Carisma, Desiree, and Virginia Rose. Of these, they found that Carisma potatoes have a GI of 53, making it the only one of the group to be classified as low-GI.

The Nicola was the next highest at 69 GI, falling into the medium-GI category. The popular Russet Burbank potatoes ranked the highest at 82 GI. In general, the potato glycemic index ranges from 53 to 111, with white potatoes typically showing up lower on the index. Leaving the skin on adds fiber, which can reduce the potato's effect on glucose.

Often, the sweet potato glycemic index is in the mid-40s.

Potato Cooking Method

The way you prepare your potatoes affects the glycemic index.

A study published by the Journal of the American Dietetic Association examined how different cooking methods affect the glucose response of potatoes. Researchers found that how potatoes are prepared plays a big role.

Instant mashed potatoes and boiled red potatoes elicited the highest glycemic response. Roasting potatoes and baking potatoes had a slightly lower glycemic response.

Concerns About Potato Glycemic Index

There has been concern over the accuracy and effectiveness of using GI for managing blood sugar. One issue is the accuracy of testing procedures. A problem arises in that the tests for glycemic index only show an average, while the glycemic index number is actually an average of those averages.

In the case of potatoes, different studies used to compute the index have results ranging from 53 to 111. Each was run on several people and only the average was reported. So, the glycemic index number itself may not be accurate enough to be helpful.

Other researchers have reported that using the glycemic index alone may not provide substantial health benefits. Some studies have shown that the index can be helpful in the management of diabetes, obesity, and cardiovascular disease risk. But beyond glycemic index, someone with diabetes should consider the intake of protein, fat, fiber, and sugar alcohols, especially surrounding meal time because they can affect blood glucose management. Solely concentrating on glycemic index may not be the best method of evaluating health and blood sugar management.

Should You Limit Potatoes?

There are different factors to consider when deciding whether or not to include potatoes in your low-GI diet.

Personalized Response

Different people have different glycemic responses to different foods. The most significant factor is how your own body reacts to a potato. You can get this information with a blood glucose meter or a continuous glucose monitor which is a more accurate tool.

This information is important if you have been diagnosed with prediabetes or diabetes. Continuous and long-term high blood sugar levels can take a toll on your body. High sugars can damage all of the organs in your body including the kidneys, eyes, skin, vagina or penis, heart, and more.  

Potato Portion Size

Potatoes have many nutritional benefits. A single serving of potatoes is considered to be 150 grams. The glycemic load (and glycemic response) will depend on how much you eat at one time and other foods you consume with the potatoes.

For instance, eating meat with a small potato and salad is a balanced meal. The fiber—if more than 5 grams—can actually reduce the spiking effect the potatoes would have on your glucose.

The same can be said for low-glycemic foods like beans and many vegetables. If you cook potatoes in a dish that has plenty of healthy fat, protein, or fiber, the spiking effect of glucose effects will be decreased.

A Word From Verywell

While potatoes can be quite high in glucose, keep in mind things you can do to reduce a blood sugar spike. If you want to eat potatoes, select a lower GI potato variety, enjoy smaller servings, and pair them with foods that counteract the glucose. Most importantly, monitor your blood glucose and see how these changes affect you personally.

For further information regarding how the potato glycemic index affects blood sugar, speak with a registered dietitian nutritionist. If managing your diabetes is too complicated, consult a certified diabetes care and education specialist.