Banana and antinutrients

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Banana and antinutrients

Post by fred »

Banana fruit seems to contain a lot of antinutrients (see below). I wonder if it is because it is not a tree but an herbaceous plant that does not need its fruits to reproduce ?
Or maybe bananas contain in reality as many antinutrients as other fruits?
I eat quiet a lot of bananas so I feel a bit worried about that!

Bananas - by Loren Cordain

Editor's note: In last week's issue of The Paleo Diet Update Dr. Cordain responded to a reader's question regarding consumption of banana peels, their nutritional value, and whether they are part of the Paleo Diet (available for download from the Newsletter section of our store page. This week's article is the second of two parts addressing the consumption of the fruit. As with last week's article, all references cited in both segments of this article are included.

Dear Dr. Cordain,

I'm a 2:18 marathoner, and have an M.S. in Exercise Science, and am making a gradual and (so far) successful switch to the Paleo Diet. My main practical struggle, obviously, is to eat enough potassium rich/alkaline fruits and veggetables. I was happy to see bananas score so high since I love bananas. Then I wondered what's in the peels. I came across this article ... ana-peels1

I was so shocked, I HAD to ask someone. Apparently, if I eat, say, 50g of banana peels (maybe one or two of them?), I will ingest 3900mg of potassium, 1200mg of sodium, 30 mg of iron, 960mg of calcium, and 3800mg of manganese. Among other things - including a probably terrifying taste - the REALLY shocking part is the comparison of the peel to its trunk. So the question is, is this really the case? And, second, what might be the alkaline score of banana peels?

Was Prot onto something? Thanks for your time.


Part 2 of Dr. Cordain's response:

Are there any potential problems with bananas themselves? If the peel is so toxic – what about the fruit? For U.S. consumers the most popular fresh fruits are oranges followed by grapes, apples, bananas, grapefruit, pineapple and peaches7. In 2007, U.S. citizens, on average, ate 26.2 lbs of bananas8. For most people without autoimmune diseases or allergies, bananas should be viewed as a nutritious and delicious fruit. However, bananas - like most plant foods - do contain certain antinutrients which may have adverse health consequences for certain people.

Like banana peels, banana fruit contains a wide variety of antinutrients, including saponins, tannins, oxalate, phytate and cyanide9. However, for the most part the concentrations of these compounds are low enough that they pose little or no health risks. The single exception is - once again - saponins. The average saponin content in six varieties of bananas and plantains was reported to be 2.4%9, which is close to the safe upper limit of 3.0%. The high saponin content of ripe bananas has the potential to increase intestinal permeability, which is a known risk factor for the development of autoimmune diseases in genetically susceptible people10. To date, no studies of ripe bananas have yet been conducted to see how they may affect intestinal permeability. Interestingly, consumption of green, non-ripe bananas actually improves intestinal permeability11. However, this outcome likely does not occur with ripe bananas because unlike green bananas, ripe bananas contain little or no indigestible starch – the element underlying the therapeutic effect of green bananas upon intestinal barrier function11.

In addition to a rather high saponin content, ripe bananas also contain another antinutrient known as thaumatin-like proteins (TLP) which are known to increase cell membrane permeability12-14 and hence intestinal permeability. The TLP content of bananas is exceedingly high, and may constitute 50% of all proteins in banana pulp14. Like saponins, TLPs are antinutrients which protect plants from fungal attack through a variety of mechanisms, including a dramatic increase in cell membrane permeability of potential pathogens and predators12-14. No studies have been conducted to verify whether TLPs actually increase intestinal permeability in living humans, but both animal and tissue culture experiments point in this direction. Because of this information, people with autoimmune diseases should use caution when including bananas in their diets.

The cocktail of antinutrients in bananas doesn’t end with TLPs, as they also contain a lectin called BanLec-I which was only discovered in 199015. As with other antinutrients, BanLec-I’s likely function is to ward off predators due to its toxic effects16. Banana lectin almost certainly crosses the gut barrier and enters circulation, as immune antibodies (IgG4) to it have been discovered in unexpected high frequencies in human blood17. As with other lectins, it seems likely that BanLec-I may be involved with autoimmune diseases because of its ability to bind antigens (proteins) from gut borne food and bacteria15, and drag them past the gut barrier in a Trojan Horse like manner. These lectin compounds, plus gut borne antigens, are then processed by immune system cells (dendritic cells) in a manner that likely evokes an immune response15,16. For an autoimmune disease to develop in genetically susceptible people, a powerful pro-inflammatory response by the immune system must first occur. Well, you guessed it: banana lectin does precisely this in animal tissue experiments by stimulating production of the pro-inflammatory cytokines (localized hormones), interferon gamma, tumor necrosis factor alpha, and interleukin 218, 19. All of these experiments indicate that bananas may represent a dietary trigger for autoimmune patients.

I’m not finished yet. Bananas contain at least two other antinutrients which may adversely impact health. For any antinutrient to arrive intact in the gut, and then cross the gut barrier into circulation, it must resist the enzymes in the gut which normally break proteins into amino acids. Intact proteins generally cannot cross a healthy gut barrier, as we normally only absorb amino acids. However, when the gut becomes leaky, proteins can cross the gut barrier, enter the bloodstream and interact with the immune system – providing they haven’t already been degraded by enzymes (proteases) from the gut. Bananas not only contain substances which promote a leaky gut (saponins and TLPs), but they also contain compounds (protease inhibitors)20 which prevent the gut’s protein degrading enzymes from doing their job. Consequently, the cocktail of antinutrients in bananas sets off a series of immunological events which are suspected to underlie the development of many autoimmune diseases10, 21.

The last antinutrients found in bananas are just plain weird. There is no other way to describe these compounds, as they are normally not found plants but in animals, where they function as chemicals in the nervous system. Bananas contain high concentrations of the neurochemicals dopamine and norepinephrine22, 23. Dopamine is a powerful antioxidant, and likely functions in bananas to protect the fruit from the oxidative stress that results from the strong sunlight and high temperatures found in tropical regions where bananas grow22. Dopamine and norepinephrine from bananas have been found to alter the bacterial flora of the gut by promoting growth of harmful gram negative bacteria, such as: Escherichia coli, Shigella flexneri, Enterobacter cloacae and Salmonella typhimurium23. All of these bacteria contain a substance in their cell walls called lipopolysaccharide (LPS), which causes a powerful pro-inflammatory response in the immune system - providing LPS breeches the gut barrier and makes contact with immune cells called macrophages and dendritic cells. Because bananas contain saponins and TLPs, which likely increase intestinal permeability, it is possible that an altered gut flora containing more gram negative bacteria may promote chronic low level systemic inflammation as LPS binds to immune system cells. However, to date no such effect of bananas has ever been demonstrated in living people.

So to summarize, chuck the banana peel and eat the banana. Bananas are a healthy, delicious fruit that should be part of modern day Paleo Diets. However, if you have allergies or an autoimmune disease, use caution when consuming this fruit. Autoimmune patients should try eliminating bananas for a few weeks or months, then add them back into their diet and monitor their symptoms carefully.

Loren Cordain, Ph.D., Professor


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Re: Banana and antinutrients

Post by RRM »

fred wrote:Banana fruit seems to contain a lot of antinutrients (see below).
Only the level of saponins seems to be high, no?
Or maybe bananas contain in reality as many antinutrients as other fruits?
I think it contains more than other fruits.
My experience is that its hard to keep on eating bananas, contrary to eating fruits such as
mango, orange or kiwi, for example, unless the banana is really, really overripe (brown).
Thats why i generally only like to consume them after using the slow juicer,
even though this yields only 30% (or so) 'juice'...
"So to summarize, chuck the banana peel and eat the banana."
I agree.
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