Sweet Potato Proteins vs. Cancer

Anti Cancer Potential of Sweet Potato Proteins

Sweet potatoes can be considered a superfood. They are one of the healthiest and cheapest vegetables on the planet. (And one day, perhaps, even off the planet, as NASA has chosen the sweet potato for space missions.) A study out of the University of Washington aimed to identify which vegetables provided the most nutrients per dollar. In my video, Anti-Cancer Potential of Sweet Potato Proteins, you can see a graph of affordability versus nutrition for different foods. The healthiest foods, like dark green leafy vegetables, may also be the cheapest, and the highest nutrient-rich food scores per dollar were obtained for sweet potatoes.

Sweet potatoes are not just packed with nutrition but may also have special cancer-fighting properties. In 1931, a unique protein was discovered in sweet potatoes. It turns out that 80% of the protein in sweet potatoes is a type of protease inhibitor with potential anticancer effects. These proteins were originally tested against leukemia and appeared to suppress the growth of leukemia cells in a petri dish.

But how would a sweet potato protein ever get into our bloodstream? As soon as most proteins hit our stomach, they start getting digested. To get around the digestion issue, researchers tried sweet potato protein against tongue cancer cells (sweet potato proteins certainly come in contact with our mouth!). Tongue cancer is often treated with chemotherapy, and most of the chemo drugs for tongue cancer have adverse effects; so, it is indispensable for us to find other therapeutic strategies. Sweet potato protein rapidly diminished viability of the cancer in vitro within a matter of days, leading the researchers to propose that sweet potatoes may be useful for human tongue cancer. But could they possibly help with other cancers as well?

Remarkably, this special class of proteins doesn’t just survive digestion, but may also be absorbed into the bloodstream intact (in at least two of the nine women with advanced cervical cancer researchers tried giving them to).

Most recently, sweet potato proteins were tried on colorectal cancer cells, one of our most common and deadly cancers. Normally, we just surgically remove the colon, but that only works in the early stages since there are often “micrometastases” outside the colon that can subsequently lead to cancer recurrence and death; so, we’ve been searching for anti-metastatic agents. Not only does sweet potato protein slow down the growth of colon cancer cells, but it may also decrease cancer cell migration and invasion.

Sweet potato consumption has also been associated with lower gallbladder cancer rates, but it has never been directly put to the test, but what’s the downside?

Sweet potatoes are one of my favorite snacks. During the harsh Boston winters during my medical training, I used to put two freshly microwaved sweet potatoes in my coat pockets as natural hand-warmers. 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 video: Best Way to Cook Sweet Potatoes.

-Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live year-in-review presentations Uprooting the Leading Causes of DeathMore Than an Apple a DayFrom Table to Able, and Food as Medicine.

Image Credit: thebittenword.com / Flickr

  • Joseph Gonzales R.D.

    Ain’t he clever :-) “I used to put two freshly microwaved sweet potatoes in my coat pockets as natural hand-warmers. When they cooled down, my hand-warmers became instant healthy snacks!” – Micheal Greger, MD

    • Porter

      Joseph: I’m approaching my sixth decade but still am not sure how to distinguish between sweet potatoes and yam. Just yesterday at Sprouts Market I asked an employee to tell me the difference among what the store called sweet potatoes and called yams (there were two varieties.). He wasn’t sure, either. Can you shed light on this?

      • Joseph Gonzales R.D.

        It always seems to get me too! There are many varieties of both and they are often used interchangeably. Both are super healthful choices. Sweet potatoes are usually more pale, and skinny shaped. Yams (like jewel) are orangish and fatter looking.

        • Tom

          Hi Joseph, yesterday someone posted a link to ebook ($1.99 for Kindle app) by cardiologist Dennis Goodman titled Vitamin K2: the missing nutrient for heart and bone health. I downloaded and read it last night. There are two other books on same subject at Kindle. You and Dr. Greger should read it. Since I have osteoporosis of spine I am back taking a calcium supplement. But now it has vitamin K2 in it. Not sure why all the doctors I talk to have never hear of it, but things are changing fast. Hope to see a video soon on its importance here. Book is well documented. Hope you and Dr. Greger read it soon.

        • Christine

          So the protein described above is in both yams and sweet potatoes ?

        • nn

          Joseph please let Thea educate you about yams/sweet potatoes.

          • Joseph Gonzales R.D.

            Don’t you know i work for the supermarkets and try to confuse people?

            Thea always helps educate me and so many on this site. Yes, please. Refer to her knowledge about sweet potatoes above. I am glad she cleared it up for me.

          • nn

            “Don’t you know i work for the supermarkets and try to confuse people?”

            Wondered about that. lol.

          • Thea

            Ah, so that’s your secret night job! Who knew?

        • mitch96

          Found this on the internets
          Color, texture and taste!!


      • Thea

        Porter: The “yams” sold in American supermarkets are just a type of orange fleshed sweet potato. According to research I have done in the past, a true yam is very starchy in comparison and is not generally available in the US. What happened was that when the orange variety came to the US, the supermarkets wanted a way to distinguish the two types of sweet potatoes. So, they used the term ‘yam’, thereby cementing untold confusion for generations to come.

        “In certain parts of the world, sweet potatoes are locally known by other names.[6] Although the soft, orange sweet potato is often called a “yam” in parts of North America, the sweet potato is botanically very distinct from a genuine yam (Dioscorea)…”
        From: https://en.wikipedia.org/wiki/Sweet_potato

      • Enthusiast

        What Sprouts is calling a yam is just a different variety of sweet potato. Yams are a completely different beast. They have a rough skin, and are very dry and starchy rather than moist and sweet like a sweet potato.

    • Dasaniyum

      haha! that made my day! He’s crazy! What else has he done in medical school besides this and the durian stink bomb?

      Also, does the protein survive the cooking process?

      • thorn324

        Dasaniyum, in one of his videos, Dr. Greger discusses the best way to cook sweet potatoes: http://nutritionfacts.org/video/the-best-way-to-cook-sweet-potatoes/

        • Diana

          Microwaved again! I am losing faith in your knowledge. Boo hoo

          • thorn324

            Diana, I don’t understand your reply. Please elaborate … specifically: what does “microwaved” mean in this context; what do you mean by “losing faith”; whose knowledge do you refer to (mine, Dr. Greger’s, someone else)? If you think my post isn’t helpful I’d like to know why so as do avoid this situation in the future. Thank you.

          • Diana

            Sorry, I just cannot believe that microwaved food is good for you when it changes the cellular structure of the food. By, faith I meant how much faith I have in Dr Greger. (A lot! LOVE his videos, research and I ordered the book and DVD. ) but I cannot believe microwaved food is ok. It would be nice to know for sure.

          • thorn324

            Diana, I recommend that in the future you reply to specific post *only* when what you have to say applies to those very posts. That way, you’ll avoid confusion on the part of the original poster. When you have a general comment to make, however, the appropriate place to type your comment is toward the top of the page, in the rectangle that says “Join the discussion.” Doing this would have saved both of us time and your comment would have made much more sense than it did. I write this, btw, not to be negatively critical but rather in hope that we all improve our communication skills. Thanks!

          • Brynda Jolly Bechtold

            cooking in any form also changes the cellular structure of food. I don’t microwave for quite a few years and took a lot to get me to do it..sweet potatoes were my first item. But microwaves cook by causing agitation of water and sugar molecules and that friction creates heat. It’s not nuclear.

        • LAURALEAH

          Well, this surprises me! I thought boiling was bad and baking would be best!! Guess I will be boiling from now on!

  • uma7

    They taste pretty bland plain what’s an easy way to make them taste great with not much effort? Lol.

    • Joseph Gonzales R.D.

      Roasting is one way. A bit more time consuming but super easy to prep. You could microwave and then make a quick and easy sweet potato pudding.

      • Ann

        Bake in the oven at 450 for an hour. They are HOT, so be careful when taking out of the oven.
        Cut open like a baked potato, add butter a little Real Maple Syrup and a little cinnamon. Yum, Yum!

        • nn

          Bake long enough for them to caramelize. Delicious with nothing added.

      • DavePL

        Thanks for posting this great recipe! It’s gotten to be one my favorites, I’m having almost every day. using an immersion blender in a bowl to mix everything.

        • Joseph Gonzales R.D.


    • rumicat

      Peel and cut into large circles, put them in a bag with a small amount of olive oil (just enough to get the spices to stick) and some chinese five spice powder, roast at 400 for 35 mintues. Tastes like pumpkin pie..

    • Julie

      Sprinkle baked sweet potatoes with avocado or chopped nuts and a little salt.; pecans and walnuts go well. Also chopped sweet potatoes make a nice addition to soups and stews.

    • Charzie

      When I’m lazy I nuke em and ladle on some vege baked beans…but baking in the oven really brings out the flavors.

    • Psych MD

      I sprinkle mine generously with pumpkin pie spice. Pumpkin pie spice isn’t exorbitantly expensive, but the typical little containers in supermarkets aren’t particularly cheap. I make my own for pennies by buying the ingredients in bulk at WinCo. Cinnamon, ginger, cloves, allspice, and nutmeg. All Greger-endorsed spices that make a superfood even more super.

    • KnowBeans

      Boil, slice, then slather with sriracha. Deviant cells that escape the clutches of the protease inhibitors get dispatched by the capsaicin.

  • Jjc

    Can you please tell if sweet potatoes are ok for patients with ck4 disease? As you know sodium, potassium, phosphorus, must be watched.

  • Ron B

    One thing I don’t understand: Regular potatoes are usually considered as not healthy.
    The differences between regular & sweet potatoes in terms of nutritional content are minor. See here for example: http://www.precisionnutrition.com/regular-vs-sweet-potatoes.

    So how come sweet potatoes are so healthy?

    • thorn324

      Although the word “potato” is common to both regular & sweet and both are tubers, they are botanically different from one another (that is, they are different genera & species: potato is Solanum tuberosum; sweet potato is Ipomoea batatas). This, by the way, brings to mind Mark Twain’s observation about the differences between “lightning” and “lightning bugs” despite the similarity in the terms!

    • uma7

      White potatoes are the rare whole plant food with a high glycemic index. Of course they are still a million times healthier than animal products.

  • dancer80

    I steam sweet potatoes in my instant pot, mash the steamed potatoes with a small amount of hot water to make puree. The puree lasts for few days, and I put a big dollop in my daily green smoothies. If I want a richer and thicker smoothie with more protein, I throw in a serving of adzuki beans which I also steam in instant pot enough for the whole week.

  • Diana

    WHAT???? Microwaved. Please check the science on THAT!

    • Thea

      Diana: Here is the science on the microwave. Have you looked through the following page yet? Every myth I have seen concerning the microwave is carefully addressed here.

      • george

        Thea:Thanks for the link. Great article. i’ve known about most of these but not seen at one place nor with this clarity.

        • Thea

          george: Exactly! It was so helpful to be able to find a single page that is so well written/easily digestible (for those willing to read it) and comprehensive.

          Thanks for feedback. Glad it helped!

  • Kim

    I’m going to try to remember that one! Sweet potatoes as hand warmers, what an awesome idea…

  • http://www.stock-soup.com/blog.html Stock Soup

    how can I tell the difference between a Yam and a Sweet Potato when many Sweet Potatoes are labeled as Yams? (see: http://www.huffingtonpost.com/2013/11/25/difference-between-sweet-potatoes-and-yams_n_1097840.html)

    • http://www.stock-soup.com/blog.html Stock Soup

      never mind, I see below

  • Cee

    Is there any evidence stating beta carotene in whole foods is not causing lung cancer in smokers and former smokers? We know this is the case for supplementary beta carotene. All these orange vegatables are loaded with bcarotene.

  • DonnaCurious

    Thanks for info on yams vs sweet potatoes! I was just about to ask when I read the responses. Good to know there are few differences in the USA.

    • mitch96

      I thought Yams were when you could not spell potato ;^) A certain person comes to mind… hummm
      I like to make a sauce out of sweet potatoes. Cook ’em however you like and then stick ’em in a food processor, season to taste. Add almond milk or veg broth to a sauce consistency. Great over other veggies

  • Thea

    Diana: I’ve heard this argument before in various forms. For example, some people claim that watering plants with water that has been microwaved kills the plants. But I’ve never heard of anyone actually doing such an experiment and having their plants die. And I’ve never actually seen that such a study was truly done in any kind of respectable way (published in a peer reviewed journal so that we have a better chance of it being an experiment that shows what you actually think it shows).

    I heard of one woman who claimed to do her own personal experiment like this. She used two types of water and claimed that the one which didn’t sprout a seed was the microwaved water. However, it turned out that the microwaved water came from the tap. Her other water was spring/bottled water. To be a true test, she would have had to have a third category that used the tap water without microwaving. Without that test, it is possible (and the far more likely explanation) that the tap water was the problem, not the microwaving.

    Bottom line: I think this is another one of those microwave myths. Do you have any evidence to the contrary?

    • Charzie

      Thea, I had to try it because I am a plant person and a microwave user and it concerned me. It’s bunk. Try it. Another BS rumor that people accept as fact because they want or need to, whatever.

      • Thea

        Charzie: Thanks for sharing. So interesting that you tried it yourself. Good for you!

      • Stewart E.

        Hey thanks for doing that. I have simply dismissed this in the past but going through it here prompted me to try this experiment. You have saved me the trouble. Yeah, somebody had to do it.

    • Lakota Clearwater

      It’s possible that someone could design the experiment in a way to demonstrate significant differences between microwaved and non-mw water, which would involve oxygen deprivation to the roots. Microwaving (or any other method of heating) depletes the water of dissolved gases, and roots need oxygen. Of course this would have nothing to do with microwaving per se, but it’s possible that this myth got started by someone who was unaware of the fact that they were introducing anaerobic conditions to the microwaved water sample.

      • Thea

        Lakota: Thank you for your post! After I submitted my post, I realized that you really need a fourth category at least – one where water is heated by any method, not just the microwave. But I didn’t know if it would be all that helpful to give a follow up post. Your post helps support this idea that it is any sort of intense heat that may be an issue.

        Also, I don’t know if the original home-experimenter poured the water on the plants while hot. It’s my understanding that plants don’t like hot water…

  • Charzie

    Ha, snacks? If I had “snacks” like that, I’d have to give up a meal. Some of us just have fat genes no matter what we eat!

    • uma7

      debunked nonsense

  • Phil

    The finest nutrition and health site I have reviewed thus far. I have been studying nutrition and health since 1965. This series is wonderful! I hope it continues.

  • Brynda Jolly Bechtold

    Okay, that is good info. There is evidence that heating water in any method, will change the structure of the molecules so it is recommended to only bring water to a mild perk before making medicinal herbal teas..don’t boil it. I think Gerald Pollack’s work with water is powerful, but there’s also some less scientific info from Daniel Vitalis. Heat just alters stuff, breaks it apart..sometimes good for opening up micronutrients and breaking cell walls, other times bad for destroying nutrients that are larger and more susceptible. I’ll have to try the sprouting procedure, thanks!

  • BB2

    Loved the hand-warmers story. I’m looking forward to hearing your audio book.

  • Psych MD

    I microwave sweet potatoes at my office because it is quick and that is all I have. I had been microwaving them at home, too, but if the potato is really fat I found it difficult to gauge the time and I’d end up with either a raw crunchy center or tough, unchewable ends. I started steaming them and they come out perfect every time. Steaming is very forgiving. I can set them on the stove in the steamer, start watching an episode of Homeland, and then go back in 20-30 minutes to a perfectly cooked, fully nutritious tater.

    • Thea

      Psych MD: Great post.

      FYI: I find that a combo of the two methods works well. I microwave, but I have 1/2 to 1 inch of water in the bottom so that it sort of steams and microwaves at the same time. I flip halfway through and I find that that system works pretty well. Just sharing an idea with you.

      One more thought: Other people have wet paper towels and wrapped them around the potato before putting them in the microwave. I tried that but found that for the bigger potatoes, it needed more moisture.

  • Psych MD

    I think I’ll crank one out right now.

  • Psych MD

    The most delicious sweet potato I’ve ever had is the Asian purple. Beautiful deep purple flesh, brimming with phytonutrients.

    • BB2

      Just had one a few minutes ago. One Asian purple sweet potato (with allspice and cinnamon), followed by 3 Peruvian blue potatoes with garlic and chives, the whole washed with some green tea… I’m feeling high already…

    • Thea

      That’s my favorite too!


    I started eating sweet potatoes, daily, about 15 years ago because I’d read they were good for the skin!! Hallelujah!!! So glad to know I have also been helping to prevent cancer all these years!!!!!

    • BB2

      Like hitting the jackpot. Congratulations :-)))

  • Bookworm

    This may be TMI but I suffer gas almost immediately after eating sweet potatoes (and regular potatoes). Any advice? Vegan for 25 years and counting. :)

  • maria

    can i have the references ?

    • largelytrue

      The blog articles have an informal referencing style. You have to follow the links and, in the case that the link points to a video on this site, look at the video’s references.

  • Psych MD

    When I steam it I usually mash it with a generous amount of soymilk and the aforementioned pumpkin pie spice. A few minutes ago I was halfway through one and had a sudden inspiration: blackstrap molasses. Made it even more delicious.

  • nn

    What a timely topic. Sweet Potatoes/Yams are on sale because of Thanksgiving. Buy a bunch, leave in the paper shopping bag and store in a dark cool place. They should keep for several months. An inexpensive way to eat them for several months.

  • Sebastian Tristan

    I always add sweet potatoes to the dishes that I cook. I’m also doing my best to find purple sweet potatoes.

  • Nick_k
    • Thea

      Nick_k: Mercola is not a source that many people around here find credible. When I did my own research on microwaves, I found the arguments against microwaves to be lacking. It’s true that you don’t want to use plastic in the microwave, but you don’t have to use plastic…

      Having just said what I did about Mercola, it’s funny to me that I’m going to refer you to the following site. This author is also not one that I normally find to be credible. But the following page is a great summary of the information available about microwaves, and it is very easy to read. The article does a great job of dispelling microwave myths. (No one is wrong about everything just as no one is right about everything.):

      Of course, no one *has* to use the microwave. I’m not trying to get you to change your mind about using the microwave. I’m just trying to stop the spread of microwave myths. I’m glad you found the information about sweet potatoes comforting. I like them too!

  • Claudia

    I’m really surprised Dr. Gregor suggests using microwaves. Besides bombarding the food with high-pulsed radiation, which negatively affects the food, it can ultimately negatively affect the body. From naturalsociety.com:

    Robert O. Becker, author of The Body Electric, stated the following on page 314 in his book:

    It’s [Microwave sickness] first signs are low blood pressure and slow pulse. The later and most common manifestations are chronic excitation of the sympathetic nervous system [stress syndrome] and high blood pressure.

    This phase also often includes headache, dizziness, eye pain, sleeplessness, irritability, anxiety, stomach pain, nervous tension, inability to concentrate, hair loss, plus an increased incidence of appendicitis, cataracts, reproductive problems, and cancer. The chronic symptoms are eventually succeeded by crisis of adrenal exhaustion and ischemic heart disease [the blockage of coronary arteries and heart attacks].

    In another book entitled Health Effects of Microwave Radiation, author Dr. Lita Lee also expressed his concern over the use of microwaves. Dr. Lee observed that the symptoms listed above could be caused by certain observations shown below.

    Lymphatic disorders were observed, leading to decreased ability to prevent certain types of cancers

    An elevated rate of cancer cell formation was observed in the blood

    Increased rates of stomach and intestinal cancers were observed

    Higher rates of digestive disorders and gradual breakdown of the systems of elimination were observed

    Read more: http://naturalsociety.com/the-dangerous-truth-behind-microwaves/#ixzz3sLDcEGmy

  • Dot

    This picture above of those sweet potatoes look so good. Is there a certain recipe any where here for those?

  • MLPrice

    So some protein manages to get into the blood stream and therefore must not be denatured in the digestive system. But you didn’t address the likely denaturation of the proteins by heating. Does the protein only get in if raw sweet potatoes are eaten? Or must one use a special way of cooking?

  • Olly

    MICROWAVED sweet potatoes… do you still use microwave? Microwave cannot produce “healthy” snacks