Are bananas really able to protect against cancer?

Today we’re talking about what happens when something sounds awesome and scientific, but isn’t really true. And bananas!


News source: uh, not news – a Facebook picture

The inspiration for today's post.

The inspiration for today’s post.

Image text: Full ripe banana with full dark patches on yellow skin produces a substance called TNF (Tumor Necrosis Factor) which has the ability to combat abnormal cells. The more darker patches it has the higher will be its immunity enhancement quality: Hence, the riper the banana the better the anti-cancer quality. Yellow skin banana with dark spots on it. Please pass/share and stay healthy.

The original science:
Guess what? Someone else already wrote an interesting blog post on this! Checking for pseudoscience in real science news (updated)

I first saw this: on Facebook

Helpful vocab:
Tumor necrosis factor (TNF) – TNF is a protein that is made by animal cells that lets them talk to each other, and it’s mostly made by cells that are part of the immune system based on information from NCBI

Fun fact: the names of genes and proteins sometimes suggest meanings to non-specialists that…have nothing to do with what the genes or proteins *do.* Otherwise Sonic hedgehog would be a much, much weirder thing than it is! (My developmental biology professor said it really was named for THAT Sonic.)

Why this is news: How about why I am sharing this, instead of why it’s news? I am sharing this because it led me to other people who are writing about how things that sound like science but aren’t science get to be really popular. And because bananas will not miraculously cure cancer, lovely as that would be, given how uncomfortable current treatments are. (Bananas are delicious, however.)

What I want to clear up: Sometimes good science, bad science, and fake science look the same. It can be hard to figure out which is which! So…how can you do it? Unfortunately (or fortunately!), you have to make a judgment call.

Here are some questions you can ask yourself to help make a decision about whether to trust a scientific-sounding claim:

– Does the person telling me this story have some reason to want me to believe it? Like, will they make a ton of cash if I believe them? Sometimes people have a secret reason for convincing you something is science.

– Does the story make sense, using logic? This applies both to the actual findings and to what it could mean. (Do you think that if bananas could cure cancer they’d be available for as little as $0.20 each, given how current American drug companies seem to work? Or that they’d not all be bought up by hospitals to treat patients without drugs or surgery?)

– Do other people agree with this story? If they do, are they experts? Beware of the logical fallacy of Appeal to Authority or the logical fallacy of Appeal to Popularity. Just because a lot of people think something’s true, or someone you trust or think is smart thinks something is true, doesn’t mean it’s true. But also, sometimes people who have spent years learning about something can really help you know if a science story is real.

Dr. Brainiac’s scientific two cents:
The way I casually talk about food and what the body does with stuff you eat when I talk to scientist friends is to try to puzzle out what going through the mouth and stomach means for that stuff. The stomach is really acidic, when you measure its pH. To try to translate some slightly subtle science to more plain language, acids help create a situation where chemicals can get changed really easily: great for breaking food into chemical bits, and bad if you need a drug to get into the body without being changed. That’s what got my attention about this image in the first place: even if TNF were in bananas, the odds of it making it into the right part of your body after going through your saliva and maybe your stomach (and maybe your intestines!) seemed really not good.

Plus, as someone who enjoys cooking, I grew up with the “cooking urban legend” that banana spots were due to sugars in the fruit.

Scientific questions I would ask next:
– Are there foods that we eat that have stuff in them that doesn’t get digested that can help fight cancer?
– If a banana turns brown on the outside, is that a reliable indicator of what’s going on chemically on the inside?

Couldn’t resist another picture. Bananas, yum!

Final thoughts: It may sometimes be discouraging to think that there’s bad science or fake science floating around out there that looks like good science, but you have the ability to figure out if it is good science! And you’re not alone in trying to do that: scientists like me are on your side.

You should also know that very smart, well-educated folks can have questions just like these. Yes, even about bananas!

Oh, and here’s a recipe I like for bananas that are starting to turn brown: Sugar Spot Banana Muffins Enjoy!


  1. Thanks for the pingback! And you might want to change the date of the article. 🙂

    1. Glad to publicize a really nice piece! (And thanks for catching the date – fixed!)

  2. you dont prove it !!

    1. I should probably mention, first, that I’m not the kind of scientist who thinks that science is about positive proof. It’s part of the idea of falsifiability, which was an idea shaped by Karl Popper. Many (or most!) scientists believe it’s possible to take an idea and show it’s wrong, but not that it’s right.

      So, have I shown convincingly (rather than proven) that bananas don’t protect against cancer? You have to make that decision for yourself. I’ve given you some ideas and talked about what other people have done that I believe, and I think they’ve figured out the truth, here.

      The interesting thing about science is that you get to make the call about whether you think we’ve figured out the truth. (The truth, of course, won’t change, whether we understand it or not.)

    2. I cannot believe these articles still get comments.

      We have thoroughly refuted the internet meme (which isn’t science) which was based a completely misunderstanding of a published article. The facts are, bananas don’t contain, produce, or synthesize tumor necrosis factor. Even if it did, it would be broken down in the intestinal tract into its constituent amino acids, all of 20 or so are exactly alike, no matter the source. Even if the TNF was in the banana and even if it could enter the digestive system intact, it could not be absorbed by the wall of the gut.

      Now, even it could get from the gut to the bloodstream, you could not possibly eat enough bananas to raise your blood level of TNF. And even if you could do that, TNF’s actions aren’t what you think it is. It might cause massive autoimmune diseases and uncontrolled immune problems.

      But science doesn’t necessary prove the negative, because people without science backgrounds tend to use the Argument from Ignorance, that is, if it’s not shown false, it must be true. Nope, in real science, if you think that a Banana has TNF and by eating it, you can cure cancer, it’s up to you to provide the evidence.

      I refuted the pseudoscience easily. There is just no chance any of this is supported by science, but if you’ve got evidence, we’re here to listen.

  3. Cytokines are not proteins – I thought you might want to know this. Thankfully, because if there is any truth in this article, it would be completely abolished if TNF was a protein i.e a chain of amino acids which would be digested and degraded in the intestine.

    you are welcome!

    1. Uh, cytokines ARE proteins.

      Not to mention the fact that many bits of digested food reach the blood well before the food makes it to the intestines, so even if TNFs were produced by bananas (which I think it’s clear they’re not), they could be taken into the body before the digested banana bits made it to the intestine.

      I appreciate your trying to help, but your argument is wrong.

      1. No, you are wrong:
        This is the original article that talks about this phenomenon My concern is that they use banana extracts on cultures of macrophages. Would TNF as a cytokine survive the digestive system? Maybe these findings should be applied to clinical therapy rather than to nutrition.

        This is what I mean: ” No IL-8 or TNF alpha was detected in any rat faecal pellets”

      2. I’ve looked at the papers you linked and reread the comments here and I think I’ve figured out the source of at least some of the confusion – it was SkepticalRaptor who was talking about the fact that TNFs would be digested, as they are just proteins. (Neither of the papers you cited says that cytokines aren’t proteins, so I think you’re still wrong on that.) The Briars et al. paper you cited, in finding that TNFs didn’t show up in rat fecal pellets after they ate TNFs, confirms that it is wrong to believe that eating a banana would cure a human cancer, because IF there were TNFs in bananas, they’d probably be digested.

        And I do think it’s important that, as SkepticalRaptor pointed out, bananas don’t make TNF in the first place – so it *does not matter* whether a TNF would survive in the intestine for this question, because it’s not something coming from bananas in the first place.

        The Iwasawa and Kawazaki paper you cited is kind of limited, in that they did look at macrophage cultures, but it’s asking a fundamentally different question – whether eating bananas might cause the body itself to make more TNFs. I don’t see that paper as the best evidence for it, which, again, supports the conclusion that eating bananas won’t cure human cancer, and I agree with you that it would be interesting to see how the work relates to the work of other laboratories.

        Does that clarify my perspective? I do want to stress that I am the author of this blog and this post, and I referred people to SkepticalRaptor’s blog post, but that’s a different person. And I think the point stands – there is no evidence I’ve encountered that eating bananas will cure cancer, and it’s not helpful to let people keep thinking that it might work. I suspect that you and I might share that opinion, though I really am not sure about your thoughts, and the only reason I said anything before is that cytokines are proteins, and you said they weren’t.


    2. As the author of the original blog post, let me repeat several points.

      1. There is absolutely no evidence that bananas produce TNF, a protein (or cytokine if you will) that has a very specific purpose in the mammalian adaptive immune system, much too complex to spend much time discussing here. Though it might be possible through random chance that a banana would evolve such a complex protein, evolution is very conservative–there simply would be no reason for a plant to evolve such a protein, so it would be selected against if ever the several thousand mutations it would take to cause the production of TNF or something that mimics it.
      2. Even if TNF would be found in a banana, it simply could not be absorbed. Maybe a tiny percentage might, but I would need some solid evidence of that, and I have found none.
      3. Even if TNF were in a banana and could be absorbed, it would be nearly impossible to consume sufficient TNF to actually induce some immune response.
      4. And finally, TNF is misnamed, which happens in science. In fact, TNF doesn’t kill tumor cells except in vitro, and excess TNF would be harmful, causing massive auto-immune reactions, and could kill.

      Whatever you may “believe” there is simply no evidence of any of these things working in a way that would convince any reasonable scientist that eating a banana would have any profound physiological effect that would kill cancers. I’m sure eating a banana is fine, I happen to love them. But they are nothing more than a carbohydrate source, nothing particularly special.

  4. Hello! This is my 1st comment here so I just wanted to give a quick shout out and
    tell you I genuinely enjoy reading through your
    blog posts. Can you recommend any other blogs/websites/forums that go over the same subjects?
    Thank you!

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