Which Sweet Potato Is the Healthiest?

Everyone loves the sweet, caramelized flavor of a sweet potato, and its health benefits make this spud a spectacular addition to your diet. Behind their colorful interior, all sweet potatoes are chock-full of nutrients, but they differ in their antioxidant content, depending on the type.

Sweet potatoes (‌Ipomoea batatas)‌ are large, starchy, sweet-tasting tuber vegetables. Unlike white potatoes that belong to the nightshade family, sweet potatoes are a member of the morning glory family. Although some people think sweet potatoes and yams are the same thing, yams come from a completely different plant related to grasses and lilies.

While you may be acquainted with only one or two types of sweet potatoes, sometimes referred to as "camote," many of the hundreds of varieties produced around the world are available in the United States. Different varieties of sweet potatoes have different flavors, sizes, shapes, textures and firmness, but they basically all feature one of three flesh colors:

• Orange flesh: These types of sweet potatoes normally have rose or reddish colored skin. They include the classic Garnet and Jewels and are the most common sweet potato. They have a slightly sweet taste and are fairly firm inside. These are the potatoes that you may mistake for yams at your grocery store.

• White or cream flesh: This type of sweet potato often has a pale copper to red or golden brown skin. The flesh is dryer in texture and tastes starchier than other types.

• Purple flesh: These potatoes have a buff-colored skin and include the Okinawan sweet potato. Okinawans are a locally grown staple of Hawaii and are quickly gaining in popularity in the U.S. because of their unique color. Purple sweet potatoes have a creamy texture and delicate, sweeter taste than their orange-fleshed cousins.

All varieties of sweet potatoes are a healthy source of complex carbohydrates which provide your body with energy needed for the proper functioning of cells, including your brain. One medium, 5-inch sweet potato, cooked, provides 23.6 grams or 8 percent of your daily value (DV) for carbs, according to the USDA.

With only 103 calories in a whole, cooked sweet potato, there is no fat or cholesterol — unless you smother your potato with butter or sour cream. Better to flavor your tuber with fresh herbs or low-fat yogurt.

All types of sweet potatoes offer 5 percent of your daily value for protein per serving, along with a significant source of dietary fiber — 3.8 grams, or 15 percent of the DV — needed for keeping your digestive system functioning properly and helping to prevent constipation.

Sweet potatoes have a nutritional profile that makes them powerful allies in preventing disease and supporting overall health. Some important nutrients that sweet potatoes contain include vitamin A and C, potassium, B vitamins, manganese, magnesium and copper.

Although most types of sweet potatoes have a similar vitamin and mineral content, an outstanding difference is their phytonutrient profile. All contain antioxidants, but the color of the flesh of a sweet potato determines the source and amount. Sweet potatoes with orange flesh are rich in carotenoids. In contrast, sweet potatoes with purple-colored flesh are rich in anthocyanins, the compound that gives them their rich, vibrant color.

Carotenoids are yellow and orange pigments, synthesized by many plants, which function as a source of vitamin A (retinol) in your body. The most common carotenoids are beta carotenes, lutein, zeaxanthin and lycopene. Carotenoids may be beneficial in enhancing your immune system and contribute to eye health.

In addition, a review published in the ‌Annals of Neurology‌ in November 2012 concluded that carotenoids may play a role in preventing or delaying Lou Gehrig's disease (ALS). Data from five long-running cohort studies including over 1 million participants found that the beta-carotene found in sweet potatoes was associated with a 15-percent reduced risk of ALS.

Anthocyanin is a flavonoid naturally found in red, purple and blue fruits and berries. In addition to being a potent antioxidant, anthocyanins may possess anti-inflammatory, anti-microbial effects, in addition to helping to protect against obesity, diabetes, cardiovascular disease and cancer, according to a study published in ‌Food and Nutrition Research‌ in August 2017.

Studies have compared the antioxidant content of white, cream and purple-fleshed sweet potatoes. One such study, published in ‌Molecular Nutrition and Food Research‌ in June 2013, concluded that purple-fleshed sweet potatoes had the highest overall level of phenolics, antioxidant content and total soluble dietary fiber.

Another study that compared white, yellow and purple-fleshed sweet potatoes confirmed the findings. Conclusions, published in ‌Preventive Nutrition and Food Science‌ in June 2016, reported that all colors of potatoes were similar in polyphenol content, but the purple-fleshed potato had the highest content of anthocyanin antioxidants, while white-fleshed sweet potatoes had the lowest amount.

If you are concerned about maintaining proper vision, it's good to know that a sweet potato contains an abundance of an important nutrient — vitamin A — known for its role in eye health. Eating one orange-fleshed potato will provide 730 percent of your DV for vitamin A, which could help prevent dry eyes, night blindness and reduce the risk of eye infections.

Sweet potatoes also have a high content of zeaxanthin, along with its isomer lutein, as reported in ‌Current Developments in Nutrition‌ in September 2018. These fat-soluble compounds are found in the retina, lens and macula of your eyes. Lutein and zeaxanthin may be helpful in improving pigment density in your macula and neutralizing damaging free radicals. They absorb harmful high-energy light waves, such as the sun's ultraviolet rays and blue light, according to Harvard Health.

It's not just the beta carotene-rich, orange-fleshed, sweet potato that may be beneficial to the health of your eyes. Purple potatoes contain a class of anthocyanins that may also keep your eyes healthy.

A study published in ‌Food & Nutrition Research‌ in June 2015 examined the association between purple sweet potato anthocyanins and growth of human retinal pigment epithelial (RPE) cells. Like carotenes, these cells provide essential functions for good vision and help your eyes absorb light and protect them from damage.

From the findings of the study, researchers concluded that purple sweet potato antioxidants boosted DNA synthesis and maintained cell survival and division. These conclusions laid the foundation for further research regarding the damage-protective activities of purple potatoes on RPE cells or human vision.

If you are among the many people who suffer from stress, anxiety or depression, eating sweet potatoes may help, due to their high magnesium content — 30.8 grams or 7 percent DV per serving, per the USDA.

Magnesium plays an essential role in nerve transmission and muscle contraction, which may be why it has been studied for its potential to prevent and treat neurological disorders, according to a review in ‌Nutrients‌, published in June 2018. Summarized findings in the review supported magnesium as a treatment for mild anxiety and multiple anxiety disorders.

A German study, published in the journal ‌MMW Fortschritte Der Medizin‌ in December 2016, analyzed the association of magnesium intake with stress reduction. Researchers administered 400 milligrams of magnesium to a group of 100 participants for a period of 90 days. The conclusions suggested that supplementing magnesium in people with physical and mental stress can help relieve restlessness, irritability, depression, lack of concentration or insomnia.

Depression and anxiety can contribute to difficulty sleeping. An amino acid in sweet potato may be beneficial for helping you relax. This compound is tryptophan; the USDA reports that sweet potatoes contain 46 milligrams or 16 percent of your DV per serving.

Tryptophan is the precursor of serotonin and melatonin. Serotonin is a brain neurotransmitter that helps regulates mood and sleep, among other things. Serotonin is often included as an ingredient in antidepressants. Melatonin is known to promote relaxation and sleep and is helpful as a sleep-aid medication.

A January 2016 review published in ‌Nutrients‌ examined the association of various levels of tryptophan, and its precursor serotonin, on emotion and cognitive reaction. Findings showed that low levels of serotonin in the brain have a negative effect on mood and depression and also contribute to impaired memory.