Sweet potatoes are native to Central and South America and are one of the oldest vegetables used by man. Christopher Columbus brought sweet potatoes to Europe after his first voyage to the New World in 1492. By the 16th century, they were brought to the Philippines by Spanish explorers and to Africa, India, Indonesia and southern Asia by the Portuguese. Around this same time, sweet potatoes began to be cultivated in the southern United States. Worldwide, about 80 million tons of sweet potatoes are grown in China each year, with Africa producing about 14 million tons, Central and South America about 2 million, and the U.S. about 1 million tons.
What people may not know is that sweet potatoes belong to an entirely different food species than either yams or the common potato. The potato is a starchy, tuberous crop from the perennial nightshade family. Yams are closely related to lilies and grasses. Compared to sweet potatoes, yams are starchier and drier.
The many varieties of sweet potatoes are members of the morning glory family, Convolvulacea. Depending upon the variety, of which there are about 400, the skin color can range from white to yellow, red, purple or brown. The flesh of the sweet potato may be almost white, cream, yellow, orange, orange-red, pink, or deep purple, although white/cream and yellow-orange flesh are most common. Sometimes this root vegetable will be shaped like a potato, being short and blocky with rounded ends, while other times it will be longer with tapered ends.
When you choose sweet potatoes as a dietary root vegetable, you are getting a truly unique type of potato that is nutritionally different from other types.
Nutrients in the Sweet Potato
The sweet potato’s rich orange hue not only adds a nice splash of colour to any dish; but, the pigment that provides the colour to the sweet potato, known as beta-carotene, has many health benefits. The intensity of the sweet potato’s yellow or orange flesh color is directly correlated to its beta-carotene content. Beta-carotene is a precursor to Vitamin A, which means that our bodies have the ability to convert beta-carotene to Vitamin A.
Vitamin A deficiencies are especially harmful to growing children. It is the leading cause of preventable blindness in children. Approximately 250,000 to 500,000 malnourished children in the developing world go blind each year from a deficiency of vitamin A, approximately half of whom die within a year of becoming blind. It has also been linked to prevention of vision loss and macular degeneration in adults.
Vitamin A also boosts the immune system, and in children with deficiencies it diminishes their ability to fight infections. In countries with no immunizations, infectious diseases such as measles have higher fatality rates. Even a mild deficiency can also be a problem, as it may increase children’s risk of developing respiratory and diarrheal infections, decrease growth rate, slow bone development, and decrease likelihood of survival from serious illness. Several recent studies have shown the superior ability of sweet potatoes to raise our blood levels of vitamin A. Too much Vitamin A can be toxic, which is a danger when taken as a supplement. However, with beta-carotene, the body will only convert as much of it into Vitamin A as it needs.
Sweet potatoes are available in most countries year-round, which make it a very reliable source of Vitamin A. Many countries are looking at increasing sweet potato crops to combat Vitamin A deficiencies. The recommended daily amount of vitamin A can be achieved with only 100 grams (3.5 ounces), less than one medium sized sweet potato. Orange-fleshed sweet potatoes may be one of nature’s unsurpassed sources of beta-carotene per gram, even more so than carrots.
Recent studies, however, have shown that beta-carotene is a valuable nutrient in its own right, wholly apart from its role as a vitamin A source. It plays an important part in the body’s defenses against free radicals that can cause damage to the cells, which can lead to chronic diseases. It also helps to internally protect your skin from sun damage by both deflecting and repairing cell damage caused by excessive UV exposure.
Yet beta-carotene only begins to tell the story of sweet potato antioxidants. Particularly in the purple-fleshed sweet potato, antioxidant anthocyanin pigments are abundant. These are concentrated in the starchy core, and may be even more concentrated in the flesh than in the skin.
Also, the antioxidant pigments have outstanding anti-inflammatory health benefits, similar to the blueberry. Certain events in the body can play a key role in the development of unwanted inflammation; the reduction of the inflammation has been clearly shown by the use of sweet potato phytonutrients in illnesses that include heart disease, arthritis and strokes. In studies, reduced inflammation has also been shown in brain tissue and nerve tissue throughout the body.
Recent research has shown that, particularly when passing through our digestive tract, sweet potato phytonutrients may be able to lower the potential health risk posed by heavy metals that can be contained in our diets, such as mercury, cadmium and arsenic.
Storage proteins—called sporamins—are produced by sweet potato plants whenever the plants are subjected to physical damage. Their ability to help the plants heal from this damage is related to their role as antioxidants. When the sweet potato is being digested inside of our gastrointestinal tract, we may get some of these same antioxidant benefits.
Colour-related sweet potato phytonutrients have an impact on blood clotting. Balanced amounts of fibrinogen, thrombin and fibrin are a key part of the body’s health and its ability to close off wounds and stop the loss of blood. However, excess amounts of these clotting-related molecules can trigger unwanted secretions of inflammatory-causing molecules. Intake of sweet potato color extracts have been shown to accomplish a reduction in inflammation, and simultaneous reduction of fibrinogen levels.
For most foods which are especially concentrated in starch, there can often be a risk of too much simple sugar release in our digestive tract, which can lead to a rapid rise in our blood sugar levels. However, sweet potatoes have the ability to potentially improve blood sugar regulation—even in persons with type 2 diabetes. Sweet potatoes contain almost twice as much fiber as other types of potatoes. The 6.6 grams of dietary fiber in a medium sweet potato helps to slow down the pace of digestion. This means their caloric energy is used more slowly and efficiently than a lower fiber carbohydrate.
Another nutrient group provided by sweet potatoes is the resin glycosides. In lab studies, these have been shown to have antibacterial and antifungal properties.
An equally amazing fact about sweet potatoes is the antioxidant capacity of all their parts. Different genes are at work in the flesh versus skin of the sweet potato producing different concentrations of antioxidants. Even the leaves of the sweet potato plant have been shown to provide important antioxidant benefits and are included in soups in many cuisines.
Buying and preparing sweet potatoes
When buying sweet potatoes, choose ones that are firm and do not have any cracks, bruises or soft spots. Sweet potatoes should be stored in a cool, dark and well-ventilated place, where they will keep fresh for up to ten days. Ideally, they should be kept out of the refrigerator in a cool, dry, dark place not above 60F /15C. If storing them at room temperature, keep the sweet potatoes in a brown paper bag, away from heat.
If you purchase organically grown sweet potatoes, you can eat the entire tuber, flesh and skin. Conventionally grown ones should be peeled before eating since sometimes the skin is treated with dye or wax. If preparing the sweet potato whole, it can be peeled after it is cooked.
Sweet potatoes can be steamed, boiled, baked, or stir fried. Boiled and mashed sweet potatoes are healthier than baked or roasted, as it has been shown to have a more favourable impact on maintaining proper blood sugar levels, and causes a higher spike in Vitamin A levels in children. However, you can lose some of the nutrients into the water.
The beta-carotene from sweet potatoes is also better absorbed when fat-containing foods are eaten along with the sweet potatoes. Only three grams of fat is needed, which is a small amount.
The best way to cook sweet potatoes is by steaming, for maximum nutrition and flavour. Adding a small amount of olive oil to the sweet potato after it has been steamed will give you the necessary fat, while avoiding the problems that come with frying food. Alternatively, adding sweet potatoes to dishes that contain foods high in fat will assist with the body’s absorption of the beta-carotene.
Sweet potatoes, once they are cooked, taste delicious even when served cold in salads and as a packed lunch. Although many people only use sweet potatoes during the holiday season, they are available year-round in most countries. Think of adding one of the most nutritious vegetables on the planet to your menu regularly throughout the year.