On Bananas, Avocados, and Ethylene

So I found out my first or second year of graduate school that I was "allergic" to bananas. It was a weird sudden thing; I used to be able to eat bananas without any ill-effects, but, all of the sudden, even a bite of raw banana would send my stomach writhing in excruciating cramps. Over the next couple of years, I tried again a couple of times but always with the same results. So it was that I resigned myself to not eating bananas. Strangely enough, however, cooked bananas seem fine. (Which is stupendous, since I love banana bread... no nuts, please.)

At the time, I did some internet searching, but I really couldn't find much about the problem, so I just assumed I was some crazy freak of nature.

Fast forward several years...

Today, I had a very tasty "Turkey Chipotle Wrap" for lunch; it had turkey, cheese, avocado, lettuce, and some chipotle sauce. About fifteen minutes after finishing it, my stomach started to take a turn for the worse. I was initially concerned about food poisoning, but after another 15 minutes or so, it felt just like the banana reaction. So I did some searching. And it turns out the Internet has grown since 2001! There's quite a list of people with exactly the same symptoms (including onset in their 20s!). Some links on this page led me to some bona fide research (I actually read an article from the Journal of Allergy and Clinical Immunology).

From what I could decipher, bananas, avocados, and kiwi (and some other fruits and veggies) contribute to something the literature calls the "latex-fruit syndrome." Scientists have isolated the problem to stem from an enzyme (a chitinase, if you're keeping score) present in lots of produce. The problem seems to be isolated to a particular group of fruits because these fruits produce ethylene, which hastens the ripening process. Something about the ethylene appears to be correlated with the chitinase causing things like severe stomach cramps. And, for the record, heating the fruit seems to inactivate the enzyme.

Ethylene produced by fruits to speed ripening is a natural process. As the concentration of the ambient ethylene increases, the fruit ripens more, and produces more ethylene, in a cycle. (This is why you put fruit in a paper bag to help it ripen; the bag concentrates the ethylene around the fruit.) However, fruit distributors are apparently using this to their advantage to control when the fruit ripens (because, clearly, they want it to be exactly ripe at the store). They pick the fruit early (before it's ripe) and then they can store it for longer periods of time. Right before they deliver it to the grocery store, they spray it down with ethylene, inducing that ripening process. Some people conjecture that this less natural ripening process contributes to the allergies. Some people with the allergy report that eating fruit they KNOW hasn't been sprayed with ethylene prevents the response.

For me, I'm not willing to take the chance. No bananas, avocado, or kiwi for me.