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Carbs in Potatoes and How They Affect Blood Sugar

Medically Reviewed by Michael Dansinger, MD on April 28, 2020

When you’re watching your blood sugar closely, carbs matter. Your digestive system breaks down carbohydrates into sugar. That sugar goes into your blood and makes blood sugar levels rise.

Potatoes make up 30% of the vegetables the average U.S. adult eats in a year. Their skin makes them rich in fiber, they’re low in calories, and they have important nutrients like vitamin C, potassium, and vitamin B6. They’re also chock full of starch, which is a carbohydrate.

But even though a potato is considered a complex “healthy” carb, your body digests these carbs faster than other kinds of complex carbs. These broken-down carbs flood your blood with sugar. This makes your blood sugar spike quickly.

Glycemic Index

To understand how a complex carbohydrate-rich food like a potato acts in your body, you need to know its glycemic index (GI).

The glycemic index is a scale that ranks carbohydrates from 0 to 100. The higher a food’s number, the faster it raises your blood sugar level. Low GI foods release sugar slowly into your body, giving it more time to store or use it. Your body digests foods that rate high on the scale faster than low ones.

  • High GI foods have a rating of 70-100.
  • Medium GI foods have a rating of 55-69.
  • Low GI foods are 55 or below.

Potatoes fall in the high GI category. A cup of them can affect your blood sugar in the same way a can of soda would. One study found that women who ate a large amount of potatoes raised their risk of diabetes. Replacing them with whole grains cut their risk. Bottom line: If you pile this veggie on your plate, it means a higher chance you’ll create blood sugar issues.

A potato’s glycemic index changes depending on how you prepare it. Some examples include:

  • Baked potato: 111
  • Boiled potato: 82
  • Instant mashed potatoes: 87
  • French fries 73

All of these ratings are in or above the high category.

Glycemic Load

Another important measure of how this vegetable can crank up your blood sugar is the glycemic load (GL). While glycemic index tells you how quickly your blood sugar will rise with certain foods, glycemic load helps you know how high it will go.

To get this number, you multiply the glycemic index rating by the grams of carbs in the food and divide by 100. You can rate your food’s glycemic load on the following scale:

  • High is 20 and over.
  • Medium is 11-19.
  • Low is 10 and under.

Baked Russet potatoes have a GL of a whopping 33. A white boiled potato has a GL of 25. Both are higher GL ratings than a serving of jelly beans or a doughnut.

Simple Potato Swaps

A diet high in spuds can make it much trickier to control your blood sugar. You don’t have to avoid them entirely, but you should keep your portions very small when you do have them. In the meantime, you can:

  • Try sweet potatoes or yams in place of a regular potato. A baked sweet potato is still on the high end of the medium range of the glycemic index, so don’t pile it on your plate. But an occasional sweet potato can satisfy your potato craving with an index of 64 instead of 111.
  • Beans can add starch to your plate like potatoes, but with much more fiber and protein.
  • Whole grains like quinoa or brown rice can give you a carb boost without the big blood sugar spike.
  • Steamed and mashed cauliflower is a lower carb stand-in for mashed potatoes.

The variety of potato you eat can also affect how quickly its sugar goes into your blood. Some, like the Carisma variety, have a GI as low as 53. In general, waxy potatoes like fingerling or red potatoes have a lower GI. Starchy types like the Russet and Idaho are on the high end of the scale.

WebMD Medical Reference

Sources

SOURCES:

Harvard T.H. Chan School of Public Health: “Carbohydrates and Blood Sugar,” “The problem with potatoes.”

USDA.gov: “ERS Charts of Note.”

OSU Extension Service: “Glycemic index and glycemic load for 100+ foods.”

Harvard Medical School: “Glycemic index for 60+ foods,” “The lowdown on glycemic index and glycemic load.”

British Journal of Nutrition: “Discovery of a low-glycaemic index potato and relationship with starch digestion in vitro.”

Tufts University Gerald J. and Dorothy R. Friedman School of Nutrition Science and Policy: “What Potatoes Have the Highest Glycemic Index?”

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