Raw sweet potatoes are high in complex carbohydrates, dietary fiber, and beta-carotene, as well as moderate contents of other micronutrients such as vitamin B6, iron, zinc, calcium, and manganese. Small differences in micronutrient density occur when baked, including a higher concentration of vitamin C. Sweet potatoes retain more beta-carotene when they are boiled, making it easier for the body to absorb this mineral. Cooking sweet potatoes with their skins on help to keep minerals like vitamin C and beta-carotene from evaporating.
Sweet potatoes are considered a healthy carbohydrate. A medium sweet potato (130 grams) contains 112 calories and 4 grams of dietary fiber. Sweet potatoes also have a low glycemic index. The higher the number on the index, the faster blood sugar levels will rise after eating. Consistently elevated blood glucose levels can lead to type 2 diabetes, weight gain, and diabetic problems, including nerve damage, kidney problems, and cardiovascular disease.
Although orange sweet potatoes are the most popular in the United States, they also come in white, yellow, pink, and purple colors. While the orange and yellow varieties are rich in vitamins and minerals, the purple and white varieties have a high antioxidant compound called flavonoids. Flavonoids have been proven to have antioxidative, free radical scavenging, anti-inflammatory, antiviral and anticancer properties.
Out of 18 foods studied and rated by the Center for Science in the Public Interest, sweet potato was ranked first in nutrition. The CSPI awarded points for the presence of dietary fiber, complex carbohydrates, protein, vitamins, and minerals. Points were subtracted for fat content, sodium, cholesterol, and caffeine. Nutritionists at CSPI recommend eating more of the foods at the top of the chart and less of the foods at the bottom.
Purple sweet potatoes, along with a variety of deep green and other brightly colored vegetables high in vitamins and minerals, are staples of the Okinawan diet, which is known for its high concentration of centenarians.