Purple sweet potatoes aren't just cool for their novelty factor — although their hue is sure to liven up any picnic table or dessert sideboard. You'll also find that purple sweet potato nutrition benefits are plentiful, with a taste and texture to rival the more familiar orange types.
What are Purple Sweet Potatoes?
Sweet potatoes, as a group, prefer hot, humid climates. Originating in Central and South America, they're now grown in other parts of the world, including warmer U.S. regions. Although the orange types may be more familiar to us, sweet potatoes can be several other colors, including purple, red, white and yellow. All make a sweeter, moister alternative to plain white potatoes.
Purple sweet potato benefits include their versatility. Use them for cold dishes like potato salad or a cracker spread, or as hot side dishes, whether as plain baked spuds or with other cubed and roasted root veggies. Their natural sweetness also means they can be used in pies and a range of other baked desserts.
The University of California's Agriculture and Natural Resources (UCANR) division notes that purple sweet potatoes labeled as "Okinawa" come from Japan, were popularized in Hawaii and have white skin. Those that have both purple skin and purple flesh are known as "Stokes," and have been bred and developed on the U.S. mainland. The purple sweet potato nutrition and flavor profiles are virtually identical for both types of purple-fleshed spuds.
Harvard School of Public Health notes that orange and purple sweet potato nutrition, along with the nutrient content of other colored sweet potatoes, are similar in many aspects. All sweet potatoes are good sources of fiber and potassium, along with vitamins A, B6 and C. They are rich in natural sugars, but their mitigating high fiber content means that they don't deliver as high a glycemic load as regular white potatoes. Orange sweet potatoes are higher in vitamin A, while purple sweet potatoes carry higher amounts of another kind of antioxidant, known as anthocyanins.
Read more: Which Sweet Potato Is the Healthiest?
Harness that Purple Power
Research conducted by UCANR determined that purple sweet potatoes deliver immunity-boosting anthocyanins, the same beneficial compounds found in other purple and blue foods like purple cauliflower, eggplant, plums and blueberries. The traditional purple sweet potato is now being grown across the country and around the world, often with the innovation of both purple skin and purple flesh. As the potatoes have grown in popularity, we've seen deeper research into the anthocyanin content of purple-fleshed sweet potatoes.
According to the Linus Pauling Institute, anthocyanins are one of six important flavonoids, which all provide health advantages when consumed. Normally found in purple, blue, and deep-red foods, anthocyanins appear to provide antioxidant protection, particularly against heart disease. This class of flavonoids also shows a positive impact on lowering blood cholesterol and stabilizing blood sugar metabolism. Because of this stabilization, they may play an important part in fighting diabetes and obesity.
A 100-gram (3.5 ounces) portion of uncooked sweet potato contains up to 1500 mg of anthocyanins. Even when cooked, the anthocyanin content of purple sweet potatoes is significantly higher than that of other blue or purple foods, including elderberries and blueberries. In addition, cooking methods like boiling, microwave and steaming did not reduce the anthocyanin content. Baking reduces the "purple power" by about 10 percent, while frying and stir-frying can cut anthocyanin content by up to 49 percent.
Counting Purple Sweet Potato Calories
According to USDA figures, a medium-large sweet potato weighing about 180 grams provides about 162 calories. The University of Hawaii nutrition support service reports that a similar-sized Okinawan purple sweet potato, specifically, has 251 calories. Granted, that's an "unloaded" sweet spud, so it doesn't factor in any toppings you might add. But because sweet potatoes have a moister, creamier texture and more intense flavor than cooked white potatoes, you may find that you don't have to add as many fats or extras to make it palatable.
Along with considering purple sweet potato calories, be sure to think about other factors such as fats and carbohydrates. Purple and orange sweet potatoes are fat-free, and don't contain any cholesterol. The sweetness does come at a carbohydrate cost, with the price being about 37 grams of carbohydrates for an average sweet potato, and 61 for an Okinawan purple specifically. But because they also provide about 25 percent of the fiber you need for the day, sweet potatoes remain a good source of complex carbs.
If you feel confident that the skin on your sweet potato is pesticide-free, make sure to eat it, to get as much dietary fiber as possible. Sweet potatoes contain both soluble and insoluble fiber, both of which provide health benefits. Insoluble fiber acts as a "broom" for other foods, helping to improve digestion. Soluble fiber helps stabilize blood sugar and cholesterol levels.
Read more: Why Potatoes With More Color Are Healthiest
Boosting Beta Carotene
UCANR's research found that purple sweet potatoes do contain beta carotene, along with the specific phytonutrients that blue and purple produce provides. That's important, because the USDA has determined that sweet potatoes as a general class yield almost twice the amount of beta carotene that you need for the whole day. Specifically, the Okinawan purple sweet potato has about 1643 units of vitamin A, according to University of Hawaii figures, which is only slightly less than the USDA's report of 1729 units of vitamin A for an average sweet potato.
Your body converts the beta carotene it receives from foods into vitamin A. In turn, vitamin A is one of the immunity-boosting nutrients that may help protect you from serious diseases, including certain cancers and heart disease, when consumed on a regular basis. Vitamin A also helps your body process and use iron properly. Taking both iron and vitamin A together has been shown to be more effective against anemia than taking either supplement alone.
Of all the vitamins, vitamin A is the one most closely associated with vision health. Along with helping the eyes process general information, retinol (vitamin A) also helps eyes adjust in the darkness. In addition, retinol is crucial for fetal development.
Punch Up Savory Recipes
Roasted root vegetables are a crowd-pleaser for Sunday dinner, but there can be a sea of oranges in your mix, including carrots, winter squash and traditional sweet potatoes. Punch up the visual effect, and vary the antioxidant content, by replacing orange sweet potatoes with purple sweet potatoes. Prefer mashed for your starches? For an extra artful look, consider swirling cooked and mashed purple potatoes into a bowl of white or orange mashed potatoes.
Of course, creating an all-purple dish is even more dramatic. Try our Purple Sweet Potato Hummus, which starts with the traditional chickpea-tahini base, but adds 1 cup of cooked Okinawan sweet potatoes for extra fiber and antioxidant protection. At under 100 calories per serving, this purple hummus offers 3 grams of fiber and 3 grams of protein.
Just when you thought sweet potato fries were already an "interesting twist" on regular french fries, along comes an even more interesting take, in the form of with LIVESTRONG.com's purple Parmesan Garlic Fries. They're under 100 purple sweet potato calories per serving, provide both fiber and protein, and are low in fat. When chunked, purple sweet potatoes can even add a beefy look to a Vegan Miso Sweet Potato Poke.
There are numerous other dishes which can reap purple sweet potato benefits by swapping white potatoes or orange sweet potatoes for purple sweet potatoes. These include potato salad, shepherd's pie, stew — and of course the basic baked potato side dish.
Switch Up Sweet Recipes
The quintessential purple sweet potato pie dessert recipe is known as sweet potato haupia pie, a Hawaiian favorite. The three-layer pie traditionally consists of a macadamia crust, a purple potato middle section, and topping of haupia, a coconut-based cream.
To keep it healthy, the University of Hawaii-Maui suggests blending the purple sweet potatoes with nonfat milk and egg whites for the middle layer, and using nonfat milk, coconut extract and artificial sweetener for the topping, instead of the traditional coconut milk and sugar. A low-fat graham cracker crust, instead of macadamia nuts, is another way to cut both calories and fat. In this way, the total haupia and purple sweet potato calorie count for a serving of the pie is only 190, with only 4 grams of fat and 13 grams of sugar.
With more nutritionists advocating adding highly nutritious ingredients like avocado, prunes and sweet potatoes into dessert recipes because they provide nutrients without adding saturated or trans fats, it's no surprise that purple sweet potatoes have their place in the world of healthy ingredient substitutions. Consider trying purple instead of orange sweet potatoes in our Chocolate Sweet Potato Frosting, for an even richer color. This healthier topping for brownies or cake is designed to add only 100 additional calories, with minimal sugars and fats.
Craving something sweet but healthy in the morning? Go purple as a variation of the LIVESTRONG.com Energizing Sweet Potato Smoothie recipe in which the spuds get lightened up with almond milk, fruit and cinnamon. You'll get plenty of antioxidants, along with fiber and protein, for a breakfast that's under 180 calories.
A list of healthier snacks and desserts developed by Mayo Clinic dieticians features several that use sweet potatoes. Instead of the familiar orange sweet potatoes, look for the purple variety to make such goodies as sweet potatoes and roasted bananas, a Caribbean mashed dish that pairs as well with ham as it does with ice cream. The Mayo Clinic's sweet potato pancakes with blueberry syrup can be doubly-purple, if you swap the orange spuds for purple ones.
Conquering Baking Challenges
One challenge involved in replacing orange sweet potatoes, or other roots, with purple sweet potatoes, is that the color isn't necessarily reliable. If acidic or alkaline ingredients are also present, the anthocyanin-tinted color of the purple flesh can change. Acidic ingredients, like lemon juice or vinegar, may lead to a reddish hue, while alkaline ingredients, such as baking soda or baking powder, can make the dish more bluish or bluish-green than purple.
This can make life difficult if you're making a quick-bread containing both purple sweet potato and baking powder, or planning a vinegar-based slaw that also contains sweet potato. It can take some experimenting, but seeking a more neutral pH in your dish often makes a difference. Tweaking your sweet potato recipes to accommodate the purple variety will likely involve balancing acid levels and acidic ingredients.
Baking soda can neutralize acidic ingredients in both sweet and savory foods, but add it only in small amounts, so that it doesn't affect the taste. Likewise, when a recipe that calls for alkanes such as baking soda or baking powder, add vinegar, lemon juice, buttermilk or yogurt to make the dish more neutral, and thereby less likely to change the purple hue.
Of course, you can also focus on desserts that don't have ingredients that might tip purple potatoes into either the blue or red zones. That traditional Hawaiian layered purple sweet potato pie, for example, not only uses neutral ingredients, but calls for preparing each component separately, so that the purple potato layer is fully set by the time the creamy top layer is added.
- University of Hawaii at Manoa: "Sweet Potato, Okinawan"
- Linus Pauling Institute: "Flavonoids"
- Wisconsin Department of Public Instruction: "Sweet Potato History"
- University of California Agriculture and Natural Resources: "Vibrant Purple Sweet Potatoes"
- Harvard School of Public Health: "Sweet Potatoes"
- US National Library of Medicine: "Effect of Domestic Cooking Methods on the Anthocyanins and Antioxidant Activity of Deeply Purple-Fleshed Sweet Potato"
- USDA My Food Data: "Cooked Sweet Potatoes"
- Mayo Clinic: "Dietary Fiber"
- NutriFacts: "Vitamin A"
- University of Hawaii at Manoa: "Sweet Potato Haupia Pie"
- University of Hawaii at Maui: "Purple Sweet Potato Haupia Pie"
- Mayo Clinic: "Sweet Potato Recipes"
- University of Maryland Extension Service: "Baking, Chemistry, and Purple Sweet Potatoes"