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A Visual Guide to Yams and Sweet Potatoes (plus How They Fit Into a Primal Eating Plan)

Posted By Mark Sisson On November 17, 2010 @ 10:49 am In Carbs,Nutrition | 168 Comments

Quick. What’s a suitable, Primal source of post-workout carbohydrates? If the title of this post and the picture to the right didn’t give you a hint then ask your nearest Primal enthusiast and they’ll tell you without batting an eye, “yams and sweet potatoes”. If, for whatever reason, you need some extra carbs “yams and sweet potatoes” is the answer. Everyone knows this, but is it true?

That’s what I’ll be exploring in today’s post. But first, what are yams and how do they differ from sweet potatoes?

In the United States, most tubers sold as yams are actually members of the sweet potato family. Your Garnets, your Jewels, the “yams” with the rich orange flesh and reddish-brown exterior, are, botanically, sweet potatoes. In fact, it’s quite likely that the vast majority of my readers – even the active ones including more carbohydrate in their diets [7] – have never tasted a true yam. The reason for this discrepancy is simple marketing: back in the mid-20th century, when orange-fleshed sweet potatoes were introduced into the United States, they were labeled “yams” to avoid confusion with the common white-fleshed sweet potato Americans were already enjoying. “Yam” was derived either from the Spanish “name” or Portuguese “inhame,” both of which come from the Wolof word “nyam,” which means “to sample” or “to taste.” Another African language uses “yamyam” for “to chew,” which should give you some idea of the starchy tuber’s importance in local diets – as well as the level of mastication required for its consumption.

Sweet potatoes, or Ipomoea batata, are native to South America, where they were domesticated at least 5000 years ago [8]. They’re also common in Polynesia, and radio carbon dating of sweet potato remains in the Cook Islands places them at 1000 AD, with most researchers figuring they date back to at least 700 AD. The Peruvian Quechua word for sweet potato is kumar, while it’s called the remarkably similar kumara in Polyenesia, prompting speculation that early South American voyagers actually introduced the tuber to the South Pacific. At any rate, they’re delicious, they’re eaten everywhere, and they have a lengthy tradition of being consumed by healthy people.

Real yams hail from the Dioscorea family of perennial herbaceous vines and include dozens of varieties, some of which grow to over eight feet long and weigh nearly two hundred pounds. Now that’s a carb refeed [9]!

Anyway, since most of us will be coming across sweet potatoes either disguised as yams or labeled correctly, let’s direct our attention to the various properties of the different sweet potato varieties.

Sweet Potatoes

The Classic Sweet Potato

This is probably what most of you picture when you think of a sweet potato – light tan skin, slightly yellow interior. It’s creamy, almost like a Yukon gold potato, and slightly sweet.

Basic sweet potatoes are strong sources of beta-carotene, manganese, and copper. A small one has 22g carbs and 3g fiber (food for your gut flora), making it the perfect post-workout [10] snack. Amazing with cinnamon [11].

The “Yams”

Garnet, Jewel, Beauregard: these are the orange fleshed, reddish-brownish-orangish skinned sweet potatoes masquerading as yams. They’re even more common than the standard sweet potato, sweeter, and contain a bit more water (you can hear it escape when you bake them). These guys cook surprisingly well in a microwave [12]. Pop ‘em in, heat, mash lightly, load with butter [13] and enjoy. You can expect to see quite a bit of them this coming Thanksgiving.

Okinawan Purple Sweet Potato

These are my current favorites. They are white skinned with a deep, brilliant purple interior that becomes velvety smooth and incredibly sweet when baked. Even better, the purple pigment is due to the vast numbers of anthocyanins – the very same beneficial antioxidant pigments that provide blueberries their brilliant color and health benefits. According to this entirely unbiased source [14], Okinawan sweet potatoes contain 150% more anthocyanins than the same amount of blueberries. That sounds reasonable, and a good general rule is the purpler the potato (or bluer the berry), the greater the anthocyanin content.

Several studies show potential benefits to purple sweet potato anthocyanins: suppression of mouse brain inflammation [15]; alleviation of brain aging [16]; reduction in cognitive deficits, inflammation, and oxidative damage in aging mouse brains [17]; potential suppression of neurodegenerative cell death, as in Alzheimer’s [18]; protection against acetaminophen-induced liver damage in mice [19]. In human males with borderline hepatitis, a beverage infused with purple sweet potato anthocyanins “significantly decreased the serum levels of hepatic biomarkers [20]”. Plus, the long-lived, fairly healthy Okinawans have traditionally used Okinawan purple sweet potatoes as a staple food. All the evidence seems to support their status as a healthy, delicious tuber.

There’s another variety that looks extremely similar but has a lightly violet interior streaked with white. It’s starchier and far drier than the Okinawans, and it doesn’t taste nearly as good. If you go looking for Okinawan potatoes in Asian supermarkets (which is the only place I’ve been able to find them consistently), inspect them carefully before buying. I once saw an old Chinese woman at one of these places snap the end of each potato off with her fingernail to check the color inside; this method works well, is relatively inconspicuous, and it’s a good way to make sure you’re getting the true Okinawan sweet potato. Just look for the deep purple flesh.

Japanese Sweet Potato, or Satsumaimo

Another Asian market mainstay is the satsumaimo, or Japanese sweet potato (can you tell I’ve been availing myself of the local ethnic markets?). I actually don’t care for this one. It’s just too sweet. Once you get it into the oven and the sugars start caramelizing, it becomes way too much for my palate. It’s honestly like eating dessert, which probably makes it sound pretty alluring for some. Look for purplish skin with a light interior (that turns golden brown with caramelizing). Give it a shot with some salty butter and maybe a dash of cinnamon and nutmeg if you want something sweet.

Yams

Dioscorea rotunda/cayenensis – The Common African Yam; “White Yam”; “Yellow Yam”

This is the true yam, with over 200 varieties in existence. Traditional preparation takes many forms, but the most common method is peeling and boiling. Fufu is mashed yam mixed with sauces, usually palm oil [21] based. There’s also the practice of drying raw yam and smashing it into a powder, or flour, or, I dunno, maybe a big pile of starch granules (sound familiar? [22]). This is called elubo. Though folks in the States and Europe rarely see it, it’s one of the most widely cultivated crops on the African continent, and by far the most popular yam in terms of sheer numbers. Look for it in African or Caribbean markets.

D. alata – The Purple Yam; “Water Yam”; “Winged Yam”

The purple yam was originally cultivated in Southeast Asia and is now the most widely distributed variety. It’s grown in Africa, Asia, the Pacific islands, the Caribbean, and it’s even wormed its way into the southern United States as a highly invasive marauding species [23]. I suspect this may be the imposter I encountered when looking for Okinawan sweet potatoes, although the purple yam has its own benefits: one study [24] found replacing rice [25] with D. alata in the diets of postmenopausal women improved blood lipids [26] (reduced LDL oxidation) and helped normalize sex hormones (increases in sex hormone binding globulin, estrone, and estradiol; a reduction in the total testosterone::SHBG ratio). A similar study with true sweet potatoes instead of yams did not have this effect. I’m not a postmenopausal woman, but maybe I’ll give it a shot next time.

D. opposita – “Chinese Yam”; Japanese “Mountain Yam”

This is cultivated in China, Japan, and Korea, but it’s made its way into the southern US, also as an invader [27] (PDF) – though US Chinese yam plants don’t appear to bear any edible yams. Too bad. It’s one of the only true yams edible raw (the Japanese serve grated raw D. opposita after lightly soaking it in a vinegar-water solution to neutralize the oxalates in the skin). The Chinese, who call it shanyao, have used it as an herbal medicine for thousands of years in the treatment of liver and kidney disease. In rats, shanyao extract seems to decrease liver and kidney damage related to alcohol abuse [28] and acetaminophen abuse [29]. I’ve seen this in Asian supermarkets here in LA, but have never tried it myself. It’s quite tasty served alongside sashimi, however.

For all these tubers, my go-to method of cooking is to toss a handful in the oven at 400 degrees F and check on them after about an hour. Some people prick them a couple times before cooking, but I usually don’t. If you’re in a rush, wrap them in paper towels and heat them in the microwave for a couple minutes before finishing them in the oven. If they’re oozing goo (listen for the squeal of escaping steam) or soft to the touch, they’re probably ready. That goo burns, so make sure you use either foil or a cookie sheet to protect your oven. This method has served me well for any sweet potato or “yam” I’ve come across. Some may take a little longer, some a little shorter, but the poke, prod, and goo methods are reliable and field-tested.

They keep well in the fridge for up to a week, so active folks eating more carbs can make a bunch at once for easy refeeds. Just reheat in a 200 degree oven or eat cold right out of the fridge. You can also smash the cooked, chilled tubers into a flat pancake and fry that up with some butter, coconut oil [30], and cinnamon. Very tasty.

Traditionally, sweet potato and yam skins are removed before consumption, so I err on the side of caution and do the same. I doubt a bit of skin is going to hurt you, though, if you decide to eat it. Most of the anti-nutrients in potatoes [31] can be found in the skin, and it seems logical to assume the same is true for yams and sweet potatoes.

Organic or conventional?

Generally, I opt for organic, but it may not matter as much with sweet potatoes. Sweet potatoes consistently show up with lower pesticide residues [32], especially when compared to normal potatoes [33]. As always, though, the best is locally grown in rich soil. Big farms may have good soil and growing practices, but at least when you buy from small farms at farmers’ markets, you get to meet the grower and ask them about their farm. Conventionally grown or big-time organic tubers may be perfectly acceptable, but they’ll be missing key minerals and micronutrients if the soil they were grown in is deficient and depleted. Plus, I find small farms produce tastier stuff as a general rule.

Sweet Potato Leaves

Though I haven’t seen them in any LA stores, sweet potato leaves are apparently quite nutritious and commonly eaten in some African countries. This study [34] (PDF) did the work for us, examining the nutritive and anti-nutritive properties of the leaves. Highlights include low levels of cyanide (30.24mg/100g), phytic acid (1.44mg/100g), and tannins (0.21mg/100g); high levels of magnesium (340mg/100g), calcium (28.44mg/100g), and manganese (4.65mg/100g). Oxalate content was pretty high, though, (308mg/100g), but half that of spinach (750mg/100g). These might be worth trying and treating like spinach or kale if you can get a hold of some.

Other Health Benefits

As we all know, foods aren’t just their macronutrient composition. Micronutrient matters as well, and it’s also important to see the food as exactly that: whole food, a package deal.

You might, for example, suppose that starchy sweet potatoes are absolutely horrible for patients with diabetes [35]. But sweet potatoes aren’t just starch; caiapo, an extract of the standard sweet potato, was given to type 2 diabetics [36]. After five months, they displayed greater glucose [37] control, higher adiponectin, and lower fibrinogen. Another study [38] on diabetic patients had similar results. It’s important to note that these were using non-caloric extracts, as opposed to actual sweet potatoes, but another study [39] found that actual sweet potatoes were beneficial to diabetic rats. Things might be different for diabetics eating actual sweet potatoes (starch included), but I think it’s pretty clear that healthy people can eat them freely – just look at the Kitavans [40], who eat a ton of yams and sweet potatoes.

There are thousands of varieties of sweet potatoes and yams. It would be impossible to document them all, and foolish to try. Just know this: they are healthy, tasty, safe sources of starch (if you go for that kind of thing) that people have been eating for a long, long time. If you’re trying to lose weight, keeping your intake to the post-workout period is probably best. If you’re looking for a dense source of carbs, I can’t imagine a better option. Of course, always keep your total carb intake goals in mind [41] if and when you add yams and sweet potatoes to your eating plan. For me, and I’d suspect most people reading, keeping carbs on the low end is high priority, and thus these starchy tubers are a welcome addition only every once and awhile and in moderation when they are added.

What do you think? Do you have a favorite sweet potato variety? Favorite preparation method? Are sweet potatoes part of your diet, and if so, how often do you eat them? Share your thoughts in the comment board and thanks for reading.

Photo Credit: Ganjin [42], deccanheffalump [43] Flickr Photos

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[7] active ones including more carbohydrate in their diets: http://www.marksdailyapple.com/primal-athlete-compromises/

[8] domesticated at least 5000 years ago: http://www.cgiar.org/impact/research/sweetpotato.html

[9] carb refeed: http://www.marksdailyapple.com/carb-refeeding-and-weight-loss/

[10] post-workout: http://www.marksdailyapple.com/post-workout-fasting/

[11] cinnamon: http://www.marksdailyapple.com/health-benefits-cinnamon/

[12] microwave: http://www.marksdailyapple.com/microwave-safety/

[13] butter: http://www.marksdailyapple.com/grass-fed-butter/

[14] unbiased source: http://www.hawaiipride.com/sweetpotato.html

[15] suppression of mouse brain inflammation: http://www.ncbi.nlm.nih.gov/pubmed/19941923

[16] alleviation of brain aging: http://www.ncbi.nlm.nih.gov/pubmed/19863544

[17] reduction in cognitive deficits, inflammation, and oxidative damage in aging mouse brains: http://www.ncbi.nlm.nih.gov/pubmed/19865488

[18] potential suppression of neurodegenerative cell death, as in Alzheimer’s: http://www.ncbi.nlm.nih.gov/pubmed/19771514

[19] protection against acetaminophen-induced liver damage in mice: http://www.ncbi.nlm.nih.gov/pubmed/19459732

[20] significantly decreased the serum levels of hepatic biomarkers: http://www.ncbi.nlm.nih.gov/pubmed/17299464

[21] palm oil: http://www.marksdailyapple.com/palm-oil-nutrition/

[22] sound familiar?: http://www.marksdailyapple.com/bread-grains-30000-years/

[23] as a highly invasive marauding species: http://www.invasive.org/eastern/species/5535.html

[24] study: http://www.ncbi.nlm.nih.gov/pubmed/16093400

[25] rice: http://www.marksdailyapple.com/is-rice-unhealthy/

[26] blood lipids: http://www.marksdailyapple.com/blood-test-markers/

[27] also as an invader: http://www.rtrcwma.org/SILinvasiveplants.pdf

[28] decrease liver and kidney damage related to alcohol abuse: http://www.ncbi.nlm.nih.gov/pubmed/12568288

[29] acetaminophen abuse: http://www.ncbi.nlm.nih.gov/pubmed/12060523

[30] coconut oil: http://www.marksdailyapple.com/coconut-oil-health-benefits/

[31] potatoes: http://www.marksdailyapple.com/paleo-potatoes/

[32] show up with lower pesticide residues: http://www.organicconsumers.org/organic/pesticide-residues.cfm

[33] potatoes: http://www.marksdailyapple.com/potatoes-healthy/

[34] study: http://www.pjbs.org/pjnonline/fin379.pdf

[35] diabetes: http://www.marksdailyapple.com/diabetes/

[36] was given to type 2 diabetics: http://www.ncbi.nlm.nih.gov/pubmed/17645559

[37] glucose: http://www.marksdailyapple.com/the-definitive-guide-to-sugar/

[38] study: http://www.ncbi.nlm.nih.gov/pubmed/12870164

[39] study: http://www.ncbi.nlm.nih.gov/pubmed/10706405

[40] look at the Kitavans: http://wholehealthsource.blogspot.com/2008/08/kitavans-wisdom-from-pacific-islands.html

[41] keep your total carb intake goals in mind: http://www.marksdailyapple.com/how-to-succeed-with-the-primal-blueprint/

[42] Ganjin: http://www.flickr.com/photos/ganjin/3983535708/

[43] deccanheffalump: http://www.flickr.com/photos/thecookscottage/3165799777/

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