My reading about annonacin, a neurotoxin found in Pawpaw, has me concerned about pawpaw consumption and long term (not acute) potentially compounding health issues. I'd like to hear what others know about this.
Annonacin is a chemical compound with toxic effects, especially in the nervous system, found in some fruits such as the paw paw, custard apples, soursop, and others from the family Annonaceae. It is a member of the class of compounds known as acetogenins.
An average-sized soursop fruit contains 15 mg of annonacin, while a can of commercial nectar contains 36 mg and a cup of infusion, 140 μg. Studies in rodents indicates that consumption of annonacin (3.8 and 7.6 mg per kg per day for 28 days) caused brain lesions consistent with Parkinson's disease. An adult who consumes a fruit or can of nectar daily over the course of a year is estimated to ingest the same amount of annonacin that induced brain lesions in the rodents receiving purified annonacin intravenously.
15mg of annonacin a day is likely to be toxic to humans. If I'm calculating correctly...1oz of pawpaw contains 215mg of annonacin. A single pawpaw is probably 2-3 oz, or 430-645mg of annonacin. We don't know if this builds up in our system, or how much per day/week/month is toxic.
Here is a journal article that speaks to Annonacin and Pawpaw specifically:
Pawpaw fruit contains a high concentration of annonacin, which is toxic to cortical neurons. Crude fruit extract also induced neurotoxicity, highlighting the need for additional studies to determine the potential risks of neurodegeneration associated with chronic exposure to pawpaw products.
An additional journal article that draws no conclusions, simply discusses the methods for measuring the annonacin levels in pawpaw. Note that these measurements were with the meat/pulp of the fruit, not the seed/skin/twigs/etc...
Brain dysfunction of many sorts is increased in Appalachia, but this may just correspond to risk factors such as smoking, drug usage and exposure to mine tailings. There's hardly a health risk out there that doesn't score higher for people within that region than for the country as a whole. And I'm assuming that people there would have a greater opportunity to eat pawpaws. But so many variables I can't imagine it being measurable.
There are many foods that are somewhat poisonous, but also nutritious. Oxalates, cyanide and other toxins are present in many edible things. The dose usually makes the poison. But it could be different when it's something that lingers rather than being washed out of the system.
You're bound to meet some resistance whenever a popular food is presented as a risk. My wife has hugely cut her rice consumption, after learning how nutritionally poor it is. Family members and other people in the Philippines, generally reject out of hand, the idea that a person could eat too much rice. But it's good to examine these things.
This compound has been discussed in other pawpaw threads on permies in the past. There's some interesting information in this one about the compound in question; specifically, certain sugars (coincidentally, or perhaps not so coincidentally, found in pawpaw fruit) are said to maybe intervene or block the toxic action. There's even a suggestion that a different sugar (that lacks the blocking action) is used in preparing the standardized extract used in some of the toxicity studies, which might (??? I'm not enough of a scientist to evaluate this bit) call some of the toxicity studies into question.
My prejudices are tickled and pleased by the notion that a fruit that contains some toxins may also contain phytocompounds that protect associated fructivores from harm. This sort of undocumented nutritional synergies are at the heart of the "eat whole foods" argument, of which I am a partisan. But I'm fully aware that we tend to believe the things we want to believe, and this is something I want to believe.