Potatoes constitute a major source of carbohydrate in the American diet. Carbohydrates used to be categorized as complex or simple, but now the best tools to determine the quality of carbohydrates are the glycemic index and the glycemic load. You might be wondering if potatoes are good carbs or bad carbs.
Carbohydrate Content
Potatoes are rich in carbohydrates. While a slice of whole-wheat bread contains about 15 g of carbohydrate, a large baked potato contains 63.2 g -- that's equivalent of four slices of bread. A cup of mashed potatoes, at 36.9 g carbs, is equivalent to more than two slices of bread. Fifteen strips of French fries provide 53.8 g of carbs, or about three and a half slices of bread, while an 8 oz. bag of potato chips contains 115.3 g of carbs, or almost eight slices of bread! Sweet potatoes have a lower carb content, with about 26.8 g of carbs, or the equivalent of about two slices of bread, for a medium-size sweet potato.
Glycemic Index
The glycemic index, or GI, represents the speed at which carbohydrate-containing foods raise blood sugar levels after eating. Values below 55 are considered low, between 56 and 69 are medium and above 70 are high. Potatoes tend to have high GI values. Compare the numbers for one serving of potatoes made in a variety of ways: baked potatoes have a GI of 85; instant mashed potatoes have a GI of 85; homemade mashed potatoes have a GI of 74; and French fries have a GI of 75. Sweet potatoes, however, have a moderate GI of 64. Because of their high GI, potatoes can make your blood sugar levels spike and then crash, leaving you craving more carbohydrates.
Glycemic Load
The glycemic load, or GL, integrates both the GI and the carb content of a serving of food. While the GI reflects the quality of carbs, the GL indicates to what extent a serving of food can raise your blood sugar levels. To obtain the GL for any food, subtract the fiber from the total carbs, multiply that number by the GI value of that food, and divide by 100. A GL below 10 is low and above 20 is high.
Potatoes not only have a high GI, but they also have a high GL, which means they have a big impact on your blood sugar levels. For example, a large baked potato has a GL of 48.1 and 15 strips of French fries have a GL of 36.5. On the other hand, a medium sweet potato has a moderate GL of 14.7. Figure the GL of the foods you eat to see what your total dietary GL is. Your daily total GL depends on your weight. Generally speaking, if you weight less than 150 lbs., keep your daily GL to about 55; if your weight is between 150 and 175 lbs., your daily GL should be about 65; and if you weight more than 175 lbs., stay below a daily GL of 80. Eating potatoes can use up a large part of your daily GL budget, so when you eat them, be careful to eat fewer other carb foods that day.
Potatoes and Health
Diets rich in foods with a high GI and GL are associated with an increased risk of heart disease and type 2 diabetes. Potatoes have both a high GI and high GL. You can have them in small quantities from time to time -- about two to three times a week -- but if you choose to include potatoes at a meal, avoid eating other carbohydrate-rich food at the same time, and choose high-quality carb foods the rest of the day.
The University of Sydney recommends reducing the amount of potatoes in your diet to reduce your dietary GI and GL to help you achieve and maintain a healthy body weight, decrease your risk of suffering cardiovascular disease and better manage your blood sugar levels. Sweet potatoes have a lower GI and GL and therefore are a healthier carb choice.
References
- Harvard Health Publications: Carbohydrates and Health: Not that Simple...or that Complex
- University of Sydney: The Glycemic Index
- "American Journal of Clinical Nutrition"; International Table of Glycemic Index and Glycemic Load Value; Kaye Foster-Powell et al; 2002
- Harvard School of Public Health: Glycemic Index and Glycemic Load for 100+ Foods
- USDA National Nutrient Database: Nutrient Data Laboratory
- Glycemic Index and Glycemic Load Tables for Glycemic Foods
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