Fortunately, from a nutrition standpoint, you have a number of good options for cooking sweet potatoes. While we have our own personal recommendation (namely, Healthy Steaming) here are some additional options that you may want to consider: Boiling: In several studies looking at the bioavailability of beta-carotene from sweet potatoes, boiling has been shown to be an effective cooking method. Consumption of boiled and mashed sweet potatoes has been shown to raise blood levels of vitamin A in children. When compared to roasting or baking, boiling has also been shown to have a more favorable impact on blood sugar regulation and to provide sweet potatoes with a lower glycemic index (GI) value. In one study, the average GI value for roasted sweet potato was 82, for baked sweet potato 94, and for boiled sweet potato 46. Stir-Frying: Multiple studies have shown better absorption of the beta-carotene from sweet potatoes when fat-containing foods are consumed along with the sweet potatoes. (It doesn't take much fat for this better absorption to take place—only 3-5 grams.) What fat makes possible is the conversion of beta-carotene into a special form called micellar form. Micelles are specialized collections of molecules that allow fat-soluble substances (like beta-carotene) to move around comfortably in non-fat environments (like our water-based bloodstream). They can also make it easier for fat-soluble substances to get absorbed from our digestive tract. Among several studies that have shown the benefits of a fat-containing meal for absorption of beta-carotene from foods sweet potatoes, one study has shown that stir-frying in oil is one specific cooking technique for sweet potatoes that can enhance the bioavailability of their beta-carotene. It's interesting to note that the sweet potato stir-fry in this study used a very low stir-frying temperature of 200˚F (93˚C) and that only 5 minutes of stir-frying were required to achieve the beta-carotene bioavailability benefits.
While we recognize boiling and stir-frying as viable options for cooking sweet potatoes, we recommend Healthy Steaming of sweet potatoes for maximum nutrition and flavor. Our basic logic here is simple. It's easily possible to add a small amount of fat (like a tablespoon of extra virgin olive oil) to your sweet potato recipe after the sweet potatoes have been cooked. In that way, you will be able to avoid any heating of vegetable oils that might damage their heat-sensitive nutrients. At the same time, with the practice of steaming, you'll be able to avoid submersion of the sweet potato in boiling water. That kind of submersion could result in the leeching of additional water-soluble nutrients from the sweet potato. Our Healthy Steaming method for sweet potatoes is quite simple: Fill the bottom of a steamer pot with 2 inches of water. While waiting for the water to come to a rapid boil, slice potatoes into 1/2-inch slices. Steam for 7 minutes and toss with our Mediterranean Dressing and top with your favorite optional ingredients. For details see, 7-Minute Sweet Potatoes.