Orange-fleshed sweet potatoes may be one of nature's unsurpassed sources of beta-carotene. Several recent studies have shown the superior ability of sweet potatoes to raise our blood levels of vitamin A. This benefit may be particularly true for children. In several studies from Africa, sweet potatoes were found to contain between 100-1,600 micrograms (RAE) of vitamin A in every 3.5 ounces—enough, on average, to meet 35% of all vitamin A needs, and in many cases enough to meet over 90% of vitamin A needs (from this single food alone).
Sweet potatoes are not always orange-fleshed on the inside but can also be a spectacular purple color. Sometimes it's impossible to tell from the skin of sweet potato just how rich in purple tones its inside will be. That's because scientists have now identified the exact genes in sweet potatoes (IbMYB1 and IbMYB2) that get activated to produce the purple anthocyanin pigments responsible for the rich purple tones of the flesh. The purple-fleshed sweet potato anthocyanins—primarily peonidins and cyanidins—have important antioxidant properties and anti-inflammatory properties. Particularly when passing through our digestive tract, they may be able to lower the potential health risk posed by heavy metals and oxygen radicals. For more details on purple-fleshed and orange-fleshed sweet potatoes, please see our Description section below.
It can be helpful to include some fat in your sweet potato-containing meals if you want to enjoy the full beta-carotene benefits of this root vegetable. Recent research has shown that a minimum of 3-5 grams of fat per meal significantly increases our uptake of beta-carotene from sweet potatoes. Of course, this minimal amount of fat can be very easy to include. In our Healthy Mashed Sweet Potatoes recipe, for example, we include 1 tablespoon of extra virgin olive oil, and with just this one tablespoon, each of our 4 servings for this delicious recipe provides 3.5 grams of fat.
Some nutritional benefits from sweet potatoes simply may be easier to achieve if you use steaming or boiling as your cooking method. Recent studies show excellent preservation of sweet potato anthocyanins with steaming, and several studies comparing boiling to roasting have shown better blood sugar effects (including the achievement of a lower glycemic index, or GI value) with boiling. The impact of steaming is particularly interesting, since only two minutes of steaming have been show to deactivate peroxidase enzymes that might otherwise be able to break down anthocyanins found in the sweet potato. In fact, with these peroxidase enzymes deactivated, natural anthocyanin extracts from sweet potato used for food coloring may be even more stable than synthetic food colorings. This benefit isn't limited to the food's appearance since the anthocyanins have great health benefits as antioxidants and anti-inflammatory nutrients.
Most dry beans and tubers have their own unique storage proteins. Soybeans have glycinins, potatoes have patatins, yams have dioscorins, and corn has zeins. While researchers have long been aware of sporamins—storage proteins in sweet potato—only recently has research shown some of their unique antioxidant properties. The potential health benefits of the sweet potato sporamins in helping prevent oxidative damage to our cells should not be surprising since sweet potatoes produce sporamins whenever subjected to physical damage to help promote healing.