Doctor's Note

Sweet potatoes are one of my favorite snacks. During the harsh Boston winters, I used to put two freshly microwaved sweet potatoes in my coat pockets as natural hand-warmers. And then when they cooled down, my hand-warmers became instant healthy snacks!

More videos on getting the most nutrition for one’s dollar:

What other vegetables might contain cancer fighting properties? See #1 AntiCancer Vegetable.

Are sweet potatoes best steamed? Should we eat the skin? Find out in my next video: Best Way to Cook Sweet Potatoes.

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  • Leslie

    ” this class of proteins doesn’t just survive digestion, but may be absorbed into the bloodstream intact” –

    could this actually be a bad thing for some people? For people with autoimmune situations, and-or for people who have food allergies, food sensitivities, etc.? I’ve been told that undigested proteins can create havoc for some people. Any thoughts on this?

  • Adrien

    Awesome. Sweet Potatoes is one of my favorite food now, thanks to Dr Greger’s wonderful video. If only it was a little bit cheaper here, I would eat it more often.

    If I have to choose 3 foods to live on, Sweet Potatoes would be definitely one of them.

    And you what will be your 3 favorites foods to live on ?

    • Tracy Minton

      I agree, sweet potatoes, or at least kabocha squash would be on the list. If I have to pick 3, it would be the sweet super star, some kind of green or veg, and either a fruit like apples, or a seed, since ground sunflower seeds, or tahini are so good on the sweet pots.

    • Thea

      Adrien: That’s a fun game, but too hard for me. Pick only three? And probably shouldn’t include chocolate…

      I could definitely include sweet potatoes in my three. If I absolutely had to restrict to only three, then I might make beans and broccoli be my other two. Or maybe broccoli and a fruit like you chose – say watermelon for me.

    • http://SmartDreams.net Gayle Delaney PhD

      Sweet potatoes, Black bean brownies, mango, green smoothies. I’m not a stickler for following directions, Adrien, but I love your question.

  • http://acupuncher.org/ Acupuncher

    I eat PURPLE Okinawan Sweet potatoes All of the time… But What do you Do with the Beautiful Purple Water From Boiling Your Sweet Potatoes… Drink it as a Tea, Thats What….Don’t Waste all of those Vitamins Dude… Yummy and Super Healthy I would have to Assume…

    • EccoLa

      Who sells these in the U.S.? And is there an organic source, since potatoes according to Dr. Greger are a very high pesticide crop?

      • AM95

        Okinawan/purple sweet potatoes can often be found at Asian markets though sometimes they an be found at high end grocery stores such as Whole Foods. They are expensive, at least where I live, as they cost around $2.50-3.00 per pound at the Asian markets.

        It seems most are sent in from Hawaii and they are non-organic. They are also required to undergo irradiation (not sure if this is a health concern or not but might be worth looking into) if they are sent to the mainland.

        • http://SmartDreams.net Gayle Delaney PhD

          Above, Ed commented that he finds the purple-flesh sweet potatoes too dry. So did I upon first bite a month ago. But in a couple of days that purple food called to me. As I sit here now enjoying a warm purple disk, I am glad to share my primitive cooking secret: I slice two cylindrical (9″long by 6-7″ round) raw purple sweet potatoes) into 1.5″? discs and microwave in covered, ventilated pot about 9″ high with 2″ of water at bottom for 8 minutes. Then I pour the purple water at bottom over the discs that soak it up. YUM YUM! Usually I mix with quicker cooking, more moist orange yams/sweet potatoes.

          • Thea

            Gayle: Thanks for sharing! I always like tips like this. I recently bought a bunch of purple potatoes and I am a microwave fan. So, I’ll probably be giving this a try. Thanks!

  • pm

    What is the best way to prepare sweet potatoes to take advantage of this cancer inhibiting effect? Is it acceptable to bake them in oven with coconut oil & sea salt as fries?

    • largelytrue

      If you want my opinion, yeah, oil is refined calories. Think of the oil as similar to a basting in sugar but probably worse on a few important metrics. Coconut oil is about as faddy as you can get. This segways nicely into the ‘official’ position that can be read from this site itself:

      http://nutritionfacts.org/video/is-coconut-oil-good-for-you/
      http://nutritionfacts.org/topics/coconut-oil/

      To work with my opinion a bit more, if you can’t enjoy your sweet potato sliced and microwaved until soft and slightly less moist, it may be that something is wrong with you and your current tastes, rather than with the sweet potato as it is. No food has truly universal appeal, but sweet potatoes get pretty close to that ideal.

    • PlantPoweredTrainer

      Coconut oil has lots of saturated fat.. Dr. Esselstyn (of the Cleveland Clinic, published studies using low fat, carb heavy, plant based diets to reverse heart disease) recommends against oils and saturated fat. Try using the tiniest amount of avocado oil and a little water (to help the oil spread) and keep an eye on them. Shake the baking sheet often to keep them from sticking and burning..

    • guesswhoiam

      I grate them raw into salads like beets and carrots and also spiralize them raw into spaghetti and toss with garlic and spices and a dash of cayenne

    • b00mer

      Hi pm,

      To make oil-free fries, you can try Jeff Novick’s method:

      Bake sweet or white potatoes
      Allow to cool completely (overnight in fridge)
      Slice into big wedges
      Broil for a few minutes to brown/char

  • val

    Awesome, just awesome! Yep, I’ve argued with folks who try to say :”eating healthy is too expensive”–GET OUT of TOWN!!! You can pretty much find sweet potatoes for $1 per pound and usually less (Walmart sells them for 88 cents a pound) and around certain holidays, you can even find them for less than that! I can usually get them 3 for $1. Thanks again, Doc!

    • Tracy Minton

      Yes, I promote what I consider to be a super simple way of preparing plant-foods. The “it’s too expensive” or “it takes too much time, or it’s too complicated” excuses are clearly from those who don’t really want to make changes. However, if people try food they like, and can learn how cheap and easy, then we will get people to awaken to the amazing benefits of a plant-based diet.

    • jem

      Sweet potatoes here in Pittsburgh are sometimes not available, but when they are, they are close to $2/lb. Yams are usually $1.50/lb bu no one has answered my questions about whether yams contain the protease being discussed here.

      • Jim Felder

        What we call “yams” in at least the US are in fact garnet sweet potatoes. So US yams/sweet potatoes should have this protein as well. Real yams are from a completely different family of flowering plants, and so it is very unlikely that real yams have this protein.

        From Wikipedia: http://en.m.wikipedia.org/wiki/Yam_(vegetable)

        “Yam is the common name for some plant species in the genus Dioscorea (family Dioscoreaceae) that form edible tubers. … though some varieties of sweet potato (Ipomoea batatas) are also called yam in parts of the United States and Canada, it is not part of the family Dioscoreaceae but belongs in the unrelated morning glory family Convolvulaceae.”

  • Brenda

    Sweet potatoes work great for a quick carry food when you’re not sure what you may have access to. When I may be out past a meal I cook up a batch of baked sweet potato disks to take with me to keep me from grabbing something unhealthy. Makes a great “ice cream,” too. Just bake cubes and freeze the thaw slightly and place in blender – add cinnamon. Yum

    • Suzanne

      Hi Brenda,
      I totally agree on the sweet potato as a “quick carry food” that can supply nutrition at any time while on the road. Here in Japan, we have “Yaki Imo” that are cooked on charcoal in the jackets by vendors and packaged in individual paper bags for easy consumption while at festivals [most days, you can also buy them individually in the grocery store in the produce section already hot].

      My favorite treat is to buy Yaki-Imo at the midnight celebration at most temples on New Year’s– it is cold out and holding this hot treat in your gloves is the perfect warm up! Check out: http://gakuran.com/the-yaki-imo-man-of-japan/#! –an introduction to traditional Japanese foodie culture– imagine a vendor pulling a cart down the street (or a tiny truck with a glowing fire on the back with his call of Yaki-imo for sale!).

      • Brenda

        That sounds really cool. Though a newer video says baking isn’t as nutritious as boiling and raw is even better. I’m thinking of using the mandolin and making sweet potato chips that are raw for a crunchy snack.

  • Coacervate

    When i worked for the soy bean folks we pushed the anti-cancer activity of Bowman-Birk, Kunitz and other protease inhibitors. Then I worked for the milk guys and we pushed the anti-nutritional terrors of protease inhibitors. Something got lost in translation. Science shouldn’t be an endless Geisha dance. Its tougher out there when you don’t have a John, but its better because you can choose your clients.

  • Arjan den Hollander.

    Great! My starch porridge is about 50% sweet potatoe before mixing with fruits. Must eat a pound a day of the stuff :)

  • Leslie

    ” this class of proteins (in the sweet potato) doesn’t just survive digestion, but may be absorbed into the bloodstream intact” -

    Also wondering if people with gut-permiability issues might be adversely effected by these undigested (sweet potato) proteins. Is this a valid concern?

  • Scott Tanner

    Also.. I believe sweet potato makes up the biggest bulk of the diet of the longest lived population on the planet. The Okinawa Japanese. I remember a nutritionfacts video in which a study examined this and recall it being a large bulk of their diet. How much sweet potato would someone need to consume to maximize it’s health properties? Could I maximize it’s potential with a single serving of baked sweet potato chips or baked sweet fries with a black bean burger or avocado sandwich for lunch? Or would I need to consume large quantities? Try blending hot mashed sweets with healthy spices (cloves, cinnamon, ginger) and a little coconut milk to make a breakfast porridge, then add any desired accoutrements like walnuts, pecans, raisins, etc.. I wonder if I could spin off a sweet potato pie using the docs recipe for healthy pumpkin pie…..

    • b00mer

      The sweet potato pie recipe sounds like a great idea. And you can probably get away with fewer dates than with the pumpkin pie.

      Regarding “dosages” :) This is something that often troubles me when I read the comments to these videos. I LOVE Dr. Greger’s videos, but to a certain extent they tend to promote the “superfood” mindset among many viewers. This video says sweet potatoes are great, so you want to know just how great a quantity you need to eat to “get the effects”. But then what about the video on mushrooms? On leafy greens? On all the grains and beans and fruits and other vegetables? I don’t think any one food should be maximized to the point where it would infringe on the realty of other healthful foods in the diet. If sweet potatoes are part of your meal, and the rest of your meal is made up of other “superfoods” like black beans, whole grain bread, & lettuce tomato onion, then that’s great!

      The Okinawans eat a lot of sweet potatoes, but what about the Nicoyans? They love their black beans. So should you try to eat more of the beans and fewer of the sweet potatoes? And of course the Sardinians aren’t eating either, but rather are filling up on whole wheat pasta and bread. So more bread and a smaller burger? I think it’s crazy to think like this. As human beings with a single stomach, we can’t eat like all of the blue zone peoples combined, but we have quite an advantage in being able to sample the best foods from each one to create a diet that is both nutrient dense and has tremendous variety and synergy.

      • Guest

        Why not both?

        I eat 2 cups of black beans and almost a pound of sweet potato daily. These things aren’t exactly going to pack pounds on you…

        • b00mer

          I think you missed my point entirely. Why not both? Because people have finite amounts of time and finite amounts of space in their stomachs and bowels. That’s great that you eat black beans and sweet potatoes every day, but what about whole grain pasta and bread, what about rice and oats and every other type of grain, what about all the beans besides black beans, chickpeas, kidney beans, tofu, lentils, peas, mushrooms, seaweed, every type of leafy green, every color of vegetable, every type of fruit, every beverage: cocoa, every type of tea, every type of herbal tea, etc, etc, etc.

          Whenever a video comes out about one specific food, comments indicate that people want to eat as much as they possibly can of that specific food, or they need to know what “dosage” they need to eat to get the healthful effects. People all of a sudden become concerned because even though they eat sweet potatoes, should they be eating more? People that drink green tea every day become concerned that they’re missing out on the benefits of coffee when the coffee video comes out. And the same types of comments on every video about every individual food. If people eat enough food, eat to satisfaction, and every individual component is health promoting, they shouldn’t have to worry about getting the proper “dosages” of any of them.

  • Ed

    I’ve tried warming up to the purple Okinawan sweet potatoes here in Hawaii but when microwaved with a wet paper towel around them they are just too dry & stiff for my taste. Is there another variety of purple sweet potato I can grow in my garden that is softer inside?

  • Jem

    Sweet potato and/or yam? Here in our Pittsburgh, PA stores the grocers mark yams as ‘sweet potatoes’. I’ve had discussions with them about that but they still equate the two. My question: is this protease found in sweet potatoes AND yams?

    • Wegan

      Yams are sweet potatoes. Not all sweet potatoes are yams.

      • jem

        Not really. They are not related botanically. Although yams and sweet potatoes are both angiosperms (flowering plants), they are not related botanically. Yams are a monocot (a plant having one embryonic seed leaf) and from the Dioscoreaceae or Yam family. Sweet Potatoes, often called ‘yams’, are a dicot (a plant having two embryonic seed leaves) and are from the Convolvulacea or morning glory family.

        • Wegan

          Nope, this is from the North Carolina sweet potato assn.:
          “What’s in a name? When it comes to the yam, a bit of confusion. What is marketed in the United States as “yams” are really a variety of sweet potato, grown in the South. A true yam is a starchy edible root of the Dioscorea genus, and is generally imported to America from the Caribbean. It is rough and scaly and very low in beta carotene”

          • b00mer

            Hi Wegan, the comment you shared does not contradict jem’s statement. I can see how you could interpret that the NCSPA is stating that “yams are sweet potatoes”, however their phrasing is leading to confusion. What they’re saying is that the vegetables seen *labelled* as yams in the US are *not yams*, but are actually sweet potatoes. Later, as they say, a true yam is something totally different from a sweet potato and is not typically seen in US markets.

      • jem

        Also, they are not the same nutritionally. That’s why I am wondering if they both have the protease. Actually, the vegetables in the picture look like yams. Sweet potatoes are normally not as orange.

  • Tracy Minton

    I just wrote a blog post about sweet potatoes, with a fun, easy recipe. Love them. As I like to say, plant-based diets have S.A.S. ~ simple, affordable, & sustainable. http://thefoodway.blogspot.com/2014/06/sweet-potatoes-with-beet-greens-apricot.html More recipes on our website w/ sweet potatoes at http://www.theplantbasedsolution.com

  • Darryl

    It’s a pity so few grocers carry sweet potato greens, as they’re similarly nutritious to other dark leafy greens.

    Some traditional cultures with a remarkable lack of Western chronic diseases have diets centered around sweet potatoes, notably the highlanders of Papua New Guinea (1, 2, 3, 4) and traditional Okinawans (5, 6, 7, 8, 9).

    • guest

      true. Although its probably because people have such a limited number of greens that they ever eat. I sometimes think my grocery store only carries the various greens they do because I will go through them as I can. Most other ppl just buy spinach, romain and regular lettuce, and maybe some kale every now and then.

    • Colin Wright

      Thanks for the great selection of links!

  • JoAnn Ivey

    Eat sweet potatoes every day. Just like the Blue Zone elder Okinawans. No oil which is inflammatory to the arterial endothelium and restricts nitric oxide. I steam or bake on parchment paper.

  • Alexandra

    earlier articles speaks to the over dose of protean.
    if it is a protease inhibitor then maybe it is anti protean which itself is good ?

    • b00mer

      Protease is a general term for an enzyme that breaks down protein, so a protease inhibitor would be inhibiting protein degradation, and would thus be considered “pro-protein” in the context of your comment.

      But importantly, the amino acid composition of plant foods (vs animal foods) does not lead to the induction of excess IGF-1, and generally speaking, on a whole foods plant based diet an unhealthily high protein intake is unlikely.

  • Sebastian Scott Engen

    I really hope someone can help me..
    The last 6 months I’ve tried
    to
    implement Dr.Gregers advise about the vegetarian/Vegan lifestyle (Wich
    made me feel vital in the begining), but lately the skin on
    my hands have become very dry and wrinkled – espasially my fingertips
    (Deep vertical lines).
    I tried looking it up on google, but couldn’t
    find any really good anwsers, other than – some saying it was a sign of
    adrenal fatigue (Must add, that I feel a bit drained).
    But sadly Dr. Greger haven’t been posting any videos on that subject, so please HELP me.. anyone… What should I do?

    Here is a list of what I eat daily:
    - I eat a B-complex vitamin to get my B12
    - I eat my flax
    - I eat my algae DHA
    - I eat my D-vitamin ( Living in the nothern Hemisphere)
    - I eat my veggies and fruits
    - I eat my nuts ( + 1 parranut daily)
    - I eat my beans and stuff
    And now i’ve tried to implement a zinc tablet…

    • largelytrue

      Was iodine deficiency not credible to you? With “adrenal fatigue” you are often scraping the bottom of the barrel and getting more pseudoscience than science. “Candida” is at least as legitimate.

      Beside continuing your search for credible information, I’d try introducing some guaranteed iodine into your diet (at recommended levels) and seeing what happens then. Take away the fish and the dairy (where in the U.S. at least, iodine gets into milk from sterilizing the teats) and start cooking your meals with minimal salt, and you will probably have closed your diet to all sources of iodine beyond what the soil provides to your produce, beans, nuts, and flax, which depends on the soil sources.

      The iodine advice may not work, but I don’t anticipate that it will lead to overt harm. Just inconvenience and a relatively small amount of money.

      On the off-chance that your last name and your concern over zinc indicates residence in a Scandinavian country with Norway as perhaps most likely, I did a really quick raw internet search and found this: http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=573268&fileId=S1368980004000679

      • Sebastian Scott Engen

        Thank you very much Largelytrue!
        So I’m properly iodine deficient.. But I must say that i’ve tried to include some seaweed in my diet (But maybe not enough?)
        Maybe I should try a different brand of seaweed, since i don’t really eat any iodised salt, fish or dairy – which the article you posted told were my best chances to get some)

        PS: I’m from Denmark. You deduction skills are brilliant! :-)

        • b00mer

          Hi Sebastian,

          While it may not be the reason for your fatigue at this point with your new diet, you may need to increase your B12. Often “B complex” type vitamin products are quite low in B12. I believe the absorption rate is only around 1%, so you have to take much more than the rda. Recommendations among plant based docs range from 250-1000 ug daily. Here is a blog entry detailing Dr. Greger’s recommendations:

          http://nutritionfacts.org/2011/08/30/3964/

          Also, perhaps you could try cronometer.com to get a snapshot of the micronutrient profile of your diet. Perhaps you’ll find a particular nutrient deficiency, if not, you can at least rule many of them out and go from there.

          • Sebastian Scott Engen

            Hi boomer,
            I just got some kelp tablets today, to insure that I got the right amount iodine.. Until I have the courage to plan the diet with sea-veggies.

            But about the B12. I take a suplement daily “Solaray Mega B-Stress” to get the B-12, which is 1000ug. So I think that should be enough with the recomendations you posted :-) (Thank you!)
            But do you know if B-vitamins can be like.. bad? Like it the ones from solaray could be “not-up-to-date” or “non-absorbable”?

            PS: Thanks for the link to cronometer!

          • b00mer

            Good luck with the sea vegetables! I’ve never been able to get into them and have been meaning to get some kelp tablets myself.

            Good to hear you’ve got a good dose of B12. In regards to supplements, there is a website called consumerlab where you pay for a membership to get access to their results for tests on various supplements. They will at least tell you if the substances/amounts advertised are actually in the product. I tried to check your brand for you, since I used to have access through a friend’s account but apparently the membership has lapsed :)

            In general, it seems well accepted that sublingual tablets are the best for absorption so if you don’t have that kind now, you may want to switch to that kind in the future.

            Enjoy cronometer! It’s pretty fun!

          • Sebastian Scott Engen

            Thank you! I hope it helps, my hands are becoming more and more creepy.. ^.^

            Well thats a relief. Might try a membership with them.. Could definaitly save me money and time in the long run. Thanks for trying btw!

            Sublingual tablets… What exactly is that? :-)

          • b00mer

            A lot of B12 supplements are labelled as “sublingual”. You place them under the tongue until they dissolve rather than swallowing them whole. They are supposed to be absorbed better that way. Hope that helps :)

    • Susan

      My skin is very dry also, but for me, I am not drinking enough water. I have a Multi-Pure water filter which greatly reduces certain industrial and pesticide poisons in my water, plus it makes my water taste better. And, when the water is cold, it is delicious.

      I suggest that you drink more water or green tea without sugar every day, like 6-8 8 ounce cups/day.

      • Sebastian Scott Engen

        Hi Susan! :-)
        Hmmm… Might be it… But I do make sure to get plenty of water, but maybe its still not enough….
        Actually I have another quistion you might be able to anwser.
        Dr.Gregers recomended daily salt intake is on about 1.5g – so my quistion is: Wouldn’t it be flushed out if you drink, lets say 3 liters daily? We need sodium for electrolyte, so is 1.5g really enough?

    • guest

      maybe only take B12, not the other synthetic vitamins.

      Go gluten-free.

      Stop the algae. Just limit/reduce your omega 6 intake.

      Flax makes me exhausted. Something in it depresses me
      physically, mentally, as well as my immune system. Same thing happens with chia and other omega 3 seeds and nuts. I know of others who have real bad experiences with flax and omega 3 seeds and nuts.

      Vitamin D pills (D2 and D3) suppress my immune system. I get exhausted.

      Eat some fruit and veggies and beans and greens and get out in the sun. And remember, plant-based is not always 100% vegan. Find “your” path.

  • cyndishisara

    I am wondering how ubiquitous this protein is as to types of sweet potato. For example are they present and in what concentration in Japanese sweet potatoes? Furthermore when shopping in conventional supermarkets is it not often hard to distinguish sweet potatoes from yams? This question has been bothering me for a while!

    • NotRappaport

      Here in the United States, it is extremely rare to see a true yam in a supermarket. True yams grow only in the tropics and are seldom sold or eaten here, though they can sometimes be found in specialty Asian or Caribbean groceries. What Americans and Canadians commonly refer to as yams are actually just dark orange sweet potatoes. What we refer to as sweet potatoes are just a lighter colored version. Sweet potatoes and true yams come from entirely different families of plants.

    • Susan

      Yams, at least organic, are more pale in color. But, the best way is to ask the produce manager.

  • Tania Belkin

    My family loves sweet potatoes. We live in Montreal Canada, so we have long and cold winters. I often buy sweet potatoes and roast them in the oven. My children can eat them every day:)

  • Susan

    Great idea: Using microwaved sweet potatoes as hand warmers. I could have used these hand warmers when I lived in ski country or even when I went to college on the Massachusetts North Shore.

    I buy Yukon Gold for my husband, who won’t eat sweet potatoes. I only eat sweet potatoes, the brighter orange interiors, the better.

    The size of the serving contributes the nutrients. See more at:

    Sweet potato, cooked, baked in skin, without salt. Read more:

    http://nutritiondata.self.com/facts/vegetables-and-vegetable-products/2667/2

  • Robert

    I love sweet potatoes, and now that I know it can be a prohibitor of some forms of cancer, I like them even more. Great information.

  • Lisa Johnson

    I love and honor sweet potatoes so much that I’ve created a business built entirely around them, with the fabulous sweetie as the main ingredient. Get yer yam on!