You may have seen a post floating around Facebook and other social media platforms (also Instagram) asserting the benefits of a fully ripe banana with dark patches on the skin. According to this message, it only takes one ripe banana a day to fight cancer! This ability, the message claims, is owed to the presence of something called TNF. It would be wonderful if eating a ripe banana everyday could lower our risk for developing cancer, so let’s look at the scientific facts behind this startling claim.
The message goes something like this: “According to the latest Japanese Scientific Research, a fully ripe banana with dark patches on the skin produces a substance called TNF (Tumor Necrosis Factor) which has the ability to combat abnormal cells. The more dark patches it has the higher its immunity enhancement quality. Hence, the riper the banana the better the anti-cancer quality. A yellow skin banana with dark spots on it is 8 times more effective in enhancing the property of white blood cells than a green skin version. Eating just 1 banana a day increases immunity.”
Since a green banana has no known cancer-fighting properties, a very ripe banana with dark patches on the skin, being eight times more effective, is, alas, still the same as a green banana. Because, you know, 8 x 0 = 0.
Tumor Necrosis Factor and Bananas
Ripe bananas have no anticancer properties (that we know of). They do not contain Tumor Necrosis Factor. And, if they did, it would not matter. Because ingesting TNF would probably not increase your levels of TNF. TNF is a protein that, if ingested, would be broken down before it was absorbed. The likelihood of any intact protein being absorbed is so remote it is completely negligible. 1Schwarcz, Joe. Monkeys, Myths and Molecules: Separating Fact from Fiction in the Science of Everyday Life. ECW Press, 2015.
So, where does this hopeful, yet absurd social media meme come from? The Japanese research mentioned in the message was a strange study done on rodents and published in a very obscure journal. These Japanese researchers, for some reason, injected banana extract into the peritoneal cavity of rodents. If you’re wondering where this is located, just translate it as “they injected it into the abdominal lining.”
This caused a slight increase in the rodents’ production of TNF. Articles that have resulted confused the issue by reporting simply that “they found increased TNF” making it seem as if they found TNF in the bananas. There was no mention of this in the actual research.
There is no connection to humans, so don’t start injecting yourself with banana puree. As well, increasing the body’s production of TNF is not without downsides. 1Schwarcz, Joe. Monkeys, Myths and Molecules: Separating Fact from Fiction in the Science of Everyday Life. ECW Press, 2015.
Tumor necrosis factor is a polypeptide that is made in the body by macrophages and lymphocytes when they are activated. TNF is made by animals. It is not made by plants. The purpose of TNF is to regulate immunity. It enhances the ability of phagocytes to fight microbes and has other functions. It is also involved, with interferons, in the apoptosis of tumor cells and cells infected by viruses, as well as in helping cells fight viruses. However, increasing the body’s production of TNF has serious side effects, such as the aggravation of arthritis and other inflammatory states.
In cancer research, TNF used to go by another name, cachectin. High levels of cachectin cause cachexia, which is the weight loss and appetite loss seen particularly in end-stage cancer. Very high levels of TNF can produce shock-like conditions, with fever, hypotension, metabolic acidosis, DIC, and diarrhea. 1Naish, Jeannette, and Denise Syndercombe Court. Medical Sciences. Saunders/Elsevier, 2015.
To be abundantly clear, there is nothing to this. Bananas do not contain TNF and eating them will not increase your production of TNF. And even if you were crazy enough to mainline banana extract, and even if it did increase your TNF, this would be a bad thing, not a good thing. I’m going to end this by quoting a fellow named Nick Theodorakis who summed it all up on the Snopes message board. I hope you don’t mind, Nick.
…It seems that the researchers (for reasons that still remain unclear to me, and I have occasionally studied TNF in the past) looked at the ability of phytochemicals in bananas to prime mouse peritoneal macrophage activation (in vivo and in vitro, or at least ex vivo), and one of the measurements was TNF production by activated macrophages. It said nothing about bananas actually having TNF.
Of course, even it was true that injecting banana extract into your stomach cavity could induce systemic TNF production, Nothing Good will come from that. TNF is one of the most potent pro-inflammatory cytokines and its production can cause a host of acute (fever, shock) and chronic (IBD, RA, etc.) pathological states. It might accidentally kill a few tumor (and non-tumor) cells along the way, stimulate some others, and have no effect on still others.
