If you have diabetes, you're mostly likely familiar with the glycemic index, a value assigned to foods that shows how fast they increase your blood glucose (sugar) levels. Some vegetables are classified as low glycemic index foods, so you may wonder where sweet potatoes fall.
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Any food with a glycemic index below 55 is considered "low glycemic." Sweet potatoes fall at 63 on the index, but this can be changed by cooking method. Learn how you can fit this moderate-GI food into your diet.
The GI of a boiled sweet potato is 63, plus or minus 6 points. GI doesn't tell you everything about the food's nutritional benefit, however.
What Is the Glycemic Index?
The glycemic index is based on a scale of how quickly a food causes your blood sugar levels to increase. The scale lists foods that have a rating of:
- 50 or less as low
- 51 to 69 as medium
- 70 and above as high
Foods low on the glycemic index tend to raise your blood sugar slowly and steadily while foods high on the index cause quicker spikes. According to Harvard Health, low glycemic index foods favor weight loss. That's not to say you should avoid all high-glycemic foods — they can be valuable for rapid recovery after exercise, to offset hypoglycemia or fuel endurance exercise.
If you're a diabetic — especially Type 1 but also Type 2 — you benefit from sticking to foods low on the glycemic index. Diabetes affects your ability to produce and utilize insulin, a hormone that helps you process glucose into cells for energy. Eating foods low on the glycemic index means you're better able to keep blood glucose under control.
In the past, recommendations were that those with diabetes should simply control their carbohydrate intake to keep their blood sugar under control. All carbs were to be avoided — from sugary sweets to fruits. The glycemic index makes the important acknowledgment that not all carbohydrates affect blood glucose the same way.
Factors that can affect glycemic index of a food include type of sugar, structure of the starch composition of the food, how processed the carb is, other nutrients in the carb, cooking method and, when it comes to fruits and vegetables, ripeness level.
For example, white rice glycemic index is 73, but brown rice, which is less processed, has a slightly lower GI of 68.
Where Sweet Potatoes Fall
Boiled sweet potatoes have a GI index of 63. This puts them in the medium glycemic category. To put sweet potatoes in context, compare them to other foods:
- Boiled white potatoes: 78
- Boiled carrots: 39
- Honey: 61
- Skim milk: 37
- Banana: 51
- Cornflakes: 81
- White bread: 75
- Watermelon: 76
Straight sugars vary in their glycemic indexes, too. Fructose has a GI of only 15, while sucrose sits at 103.
Cooking method plays a large role in the glycemic index of sweet potatoes, explained research published in the Open Nutrition Journal in 2012. They reported that steamed sweet potato has a GI of 63, while baking raises the GI to 64 and microwaving increases it to 66. Dehydrated and raw sweet potato has a low glycemic index value of 41.
The reason cooking changes the sweet potato glycemic index has to do with the starch. Heating the potato breaks down starch granules to make them easier to digest, which makes them quicker to boost blood sugar levels.
Sweet Potato GI and Healthfulness
Even though sweet potato doesn't fall into the category of low glycemic index foods, it offers a lot of health benefits and makes a positive contribution to everyone's diet — including diabetics. One cup of mashed sweet potato (with nothing added) has 249 calories, 8 grams of fiber, 2.3 milligrams of iron and 754 milligrams of potassium as well as some magnesium, calcium and phosphorus.
Food Research International published research in November 2016 further explaining other nutrition benefits of sweet potatoes. These starchy vegetables contain ample carotenoids, anthocyanins and phenolic acids, all of which are valuable antioxidants. Antioxidants combat free radicals, which are elements you breathe in from pollution, consume in your diet and apply to your skin. Free radicals are a major cause of cell damage that leads to aging and chronic disease.
Does GI Matter?
A meta-analysis published in Nutrients in October 2018 showed little relationship between glycemic index and physiological measures of disease risk. The researchers note that other measures of dietary value, such as fiber and vitamin content, are more likely to predict the health benefits of a food.
This meta-analysis confirmed earlier research published in the Journal of the American Medical Association in June 2015. The study confirmed that using the glycemic index to select specific foods may not improve cardiovascular risk factors or insulin resistance.
Glycemic index may have relevance when it comes to cognitive function in older adults, however. A meta-analysis published in Advances in Nutrition in March 2014 found inconsistency in the research comparing glycemic index and cognitive function, but concluded that a low-GI meal may favor cognitive function in adults. So, if you have a big paper due or a major, complex work task ahead of you, consider sticking to low-GI foods such as protein, greens and seeds.
But, the glycemic index still holds a lot of relevance for those with diabetes. A study published in a March 2018 issue of Nutrients aimed to clear up confusion about the effectiveness of using the glycemic index as a tool for managing glucose response in Type 2 diabetics. It concluded that a low-GI diet is more effective in controlling fasting blood glucose than a diet with a higher GI.
Some people use GI to help them craft a diet that promotes weight loss. A meta-analysis published in Obesity Review in February 2019 found that low-GI diets seem moderately effective in helping people lower their body weight, but people do have trouble adhering to them.
- Glycemic Index Foundation: "What Is GI?"
- The Open Nutrition Journal: "Glycemic Index of Sweet Potato as Affected by Cooking Methods"
- Harvard Health Publishing: "Glycemic Index for 60+ Foods"
- USDA National Nutrient Database: "Sweet Potato, Cooked, Boiled, Without Skin"
- Nutrients: "Relevance of the Glycemic Index and Glycemic Load for Body Weight, Diabetes, and Cardiovascular Disease"
- Journal of the American Medical Association: "Effects of High vs Low Glycemic Index of Dietary Carbohydrate on Cardiovascular Disease Risk Factors and Insulin Sensitivity"
- Advances in Nutrition: "The Influence of Glycemic Index on Cognitive Functioning: A Systematic Review of the Evidence"
- Nutrients: "The Effect of Dietary Glycaemic Index on Glycaemia in Patients With Type 2 Diabetes: A Systematic Review and Meta-Analysis of Randomized Controlled Trials"
- Food Research International: "Chemical Constituents and Health Effects of Sweet Potato"
- Obesity Reviews: "Low Glycaemic Index Diets as an Intervention for Obesity: A Systematic Review and Meta-Analysis"