The Glycemic Index for Sweet Potatoes

Rich in vitamin A and beta-carotene, the sweet potato offers complex carbohydrates along with antioxidant nutrients. If you're watching the glycemic index of your foods you may be surprised by the sweet potato's rating. Starchy sweet potato ranks low on the glycemic index scale, which measures a food's effect on your blood sugar on a scale of one to 100.

Sliced and whole sweet potatos on a wood table. (Image: margouillatphotos/iStock/Getty Images)

Importance of Glycemic Index

The glycemic index helps measure a food's impact on your blood sugar levels. Foods with a high glycemic index have a rapid effect on your blood sugar. Consuming these foods causes a blood sugar spike, which in turn leads to blood sugar crash. Low glycemic index foods increase your blood sugar levels gradually, so your blood sugar remains more stable after your meal.

Glycemic Index of Sweet Potato

The way you prepare sweet potatoes makes a difference in their GI. The GI of a 150-g sweet potato, boiled with its skin for 30 minutes, is 46. That number rises to 94 if the same sweet potato is baked for 45 minutes. These dramatic differences come from the way the starches in sweet potatoes gelatinize during cooking. Foods that turn viscous, or jelly-like, in your digestive tract have a lower GI because the gelatinous substance slows the release of the nutrients in the food. Baking your sweet potatoes instead of boiling them changes the quality of their starches and transforms this root vegetable from a moderate-GI food to a high GI-food.

Glycemic Load

The glycemic load is a way to take a food's carbohydrate content into account when figuring its impact on blood sugar. The GL considers both the quality and quantity of the carbohydrates in a food. A boiled sweet potato has a GL of 11, compared to a GL of 42 for a baked sweet potato. Because the GL doesn't take a food's nutritional content into account when measuring its metabolic effects, it's important to consider the health benefits of the sweet potato's vitamins and phytonutrients when making your food choices.

Carbohydrates and Fiber

A 150-g sweet potato baked in its skin offers 31 g of carbohydrates with only 135 calories and no fat, making it a low-calorie, virtually fat-free source of energy. A single sweet potato has 3.8 g of fiber, which regulates bowel function and may help lower your low-density lipoprotein levels, commonly known as bad cholesterol. Sweet potatoes' fiber content contributes to its place on the glycemic index scale -- it slows digestion, which lowers glycemic index, explains Utah State University.

Suggestions

Choose sweet potatoes with an orange hue; the deeper the color, the more beta-carotene the sweet potato contains. The sweet potato's skin, with its high concentration of vitamins and phytonutrients, deserves to be included in your meals. Omit marshmallows, sugar, and other sweeteners; they'll add to the GI and caloric content of your recipes. Season mashed, unpeeled sweet potatoes with cinnamon and nutmeg for a naturally sweet vegetable dish.