FOOD, FACTS and FADS

Exploring the sense and nonsense of food and health

What’s Sweet about the Sweet Potato?

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Sweet potatoes

Image via Wikipedia

The potato has been in the news lately about its ability to contribute to our waistlines.   The study was done by Harvard researchers with one main conclusion: “Daily consumption of an extra serving of spuds – french fried, sliced into crispy chips, mashed with butter and garlic, or simply boiled or baked – was found to cause more weight gain than downing an additional 12-ounce can of a sugary drink or taking an extra helping of red or processed meats.

But what about the sweet potato- often touted as a healthier alternative to the white potato?  Here are the facts?  I compared a baked white and sweet potato (100 grams) for nutrient content.

Nutrient Baked White Potato Baked Sweet Potato
Calories 188 180
Protein (g) 5 4
Carbohydrate (g) 43 40
Fiber (g) 4 6
Calcium (mg) 30 76
Iron (mg) 2 1
Potassium (mg) 1080 950
Magnesium (mg) 57 54
Sodium (mg) 20 72
Folate (ug) 57 12
Vitamin B6 (mg) 0.6 0.6
Vitamin A (ug) 2 1922
Vitamin  C (mg) 19 40
Vitamin E (mg) .08 1

 

At first glance, the nutritive content seems to be quite similar in calories, so weight gain may be similar for each serving of either  The main differences are in the antioxidant nutrients, vitamin A, C, and E.

When the glycemic loads are compared, there are no dramatic differences either.  The sweet potato has a GL of 17; the baked white potato is slightly higher with 26; boiled white potato comes in at 14; mashed potatoes at 17; and yams at 13.

Why does the sweet potato have a better reputation? First of all, many Americans do not eat sweet potatoes. According to a 2010 survey, the average American ate a mere 5.2 pounds of sweet potatoes per year.  The average amount of white potatoes each person consumes each year in the U.S is about 117 pounds.

The preparation method is a huge factor – we pile butter, sour cream, cheese, and bacon on baked white potatoes. We fry them in oil as French fries and chips.  People often eat sweet potatoes baked or boiled, not fried.  That’s a big difference in calories.

The sweet potato wins hands down when it comes to its antioxidant content. From the NC Sweet Potato Commission, “Antioxidants play a role in the prevention of heart disease and cancer, and sweet potatoes supply plenty of the antioxidants, vitamin E and beta-carotene. These substances are effective in neutralizing free radicals, which are responsible for damage to cell walls and cell structures. Vitamin E also protects against heart attack and stroke by reducing the harmful effects of low-density cholesterol and preventing blood clots.

Antioxidants are essential for good brain functioning and in delay in the effects of aging on the brain. A low level of vitamin E has been linked with memory loss. A Columbia University study showed a delay of about seven months in the progression of Alzheimer’s disease when subjects consumed high levels of vitamin E. This fat-soluble vitamin is found mainly in high-fat foods such as oils, nuts, and avocados. Only the sweet potato provides vitamin E without the fat and calories.

Sweet potatoes contain 1,922 mcg – RAE of beta-carotene (vitamin A) in one cup, which is more than the USRDA. You would have to eat 16 cups of broccoli to consume the same amount of beta-carotene. Health professionals believe that carotenoids give protection from the formation of free radicals and are chemoprotective against cancer.

The Finnish study of 10,000 smokers, reviewed in the New England Journal of Medicine in 1994, tested the effects of taking beta-carotene supplements to prevent lung cancer. It was based on the earlier finding that individuals who have higher blood levels of beta-carotene have a lower incidence of lung cancer. To the researchers’ horror, those who took the supplements actually had a higher rate of lung cancer and the study was discontinued. Researchers concluded that beta-carotene has a protective effect only when consumed in food, the original and best source. The nutrient-packed sweet potato is the richest source of this protective substance.

The sweet potato – known as kumara in Polynesian cultures is a member of the morning glory family of which many species are poisonous.  It is native to Peru and cultivated in many New World areas.  Spanish explorers introduced them to the Polynesian islands, Africa, Asia, and Europe.

The tubers are a staple food for many populations and have purple, red, or yellow skins and orange or white flesh. They contain phytochemicals like  quercetin (anti-inflammatory) and chorogenic acid, an antioxidant.

A study looked at the effects of the sweet potato on people with type 2 diabetes. The 2008 study in Diabetes, Obesity, and Metabolism reported that an extract of sweet potato, caiapo, improved insulin sensitivity and blood glucose levels in people with type 2 diabetes.

Culinary Confusion: Yam and Sweet Potato

What Americans call yams aren’t yams. They are a darker kind of sweet potato, native to the Americas.  The true yam, found in Africa and Asia, is a large, starchy root that can grow six feet underground, which makes it difficult to dig up.  According to Alan Davidson, a food writer, “It was probably slave traders who introduced the sweet potato to Africa, where it was called igname or nyam, which simply means “yam”.  Since that time the sweet potato has been steadily displacing the true yam as a major carbohydrate food in tropical Africa.”

Folklore Claims.

There are some health claims attributed to sweet potatoes and wild yams that surface frequently in the popular press.  These include treatment of HIV, diverticulosis, stomach and muscle cramps, asthma, vascular disease, menopausal symptoms and gallstones.  They have also been touted to help with arthritis and other rheumatic disorders.

Both sweet potatoes and yams in addition to its high carotene content, contain healthy phytochemicals such as saponins, flavonoids such as beta-sitosterol, alkaloids, and tannins found in tea.  There is a good chance that they account for the high level of lycopene found in Okinawans who consume a high amount of sweet potatoes called imo. Lycopene is a powerful antioxidant and carotenoid that has been found in tomato products and has been strongly associated with a reduced risk for prostate cancer.

Bottom Line:

When eaten in moderation, sweet potatoes may be an excellent alternative choice for the white potato and may not contribute as much to our waistlines.  They do contain starch, but also provide a lot of healthy phytonutrients often found in highly colored pigmented vegetables.  Let’s not load them with sugar or those dreadful little marshmallows often served at Thanksgiving dinner tables.

EAT WELL

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One thought on “What’s Sweet about the Sweet Potato?

  1. Pingback: Guest Post: Yams from Jen | Alison Amazed

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