The most delicious thing I’ve ever eaten was an unnamed hybrid of two fruits in the Annona genus, which I bought at the Pinecrest farmers’ market in Miami. I can no longer remember what it was called and I never saw the fruit again. My wife says it wasn’t a dream, but she might be lying to spare my feelings.
In any case, annona fruits are real. They are full of hard black seeds, they’re disconcertingly soft when ripe, and they tend to appear sort of lumpy or haphazardly put together. The genus includes a large number of tropical species, including the ubiquitous soursop (also called graviola or guanabana), the cherimoya or custard apple, and the gigantic junglesop (one of the largest fruits in the world). The only temperate species is the pawpaw, which grows throughout the eastern United States and is sometimes referred to as a “poor man’s banana” or an “Ozark banana.” There’s also the turpentine-flavored “pond apple,” which is native to South Florida.
Annona fruits are an important food in the tropical world, and they’re widely used in folk medicine as well. An ancient Jamaican man at the farmers’ market sold me soursop leaf powder and said it would help me sleep, relieve headaches and muscle pain, prevent me from getting cancer, and cure any cancerous growths I had already. He gave me some typed documents that spelled all this out. I affected an air of critical distance, but never in a million farmers’ markets would I have failed to purchase his leaf powder. I was having trouble sleeping at the time, partly because of muscle pain. I thought: What harm could it do?
It’s not an easy question to answer. Nature’s Sunshine sells a pawpaw twig extract called Paw Paw Cell-Reg. Apparently it’s popular with cancer patients, who say it helps prevent tumor growth and improves overall outcomes. In a study published in 2010, Coothankandaswamy et al. confirm that compounds called “annonaceous acetogenins,” which are found in all annona fruits, help to suppress the growth of new blood vessels in certain kinds of cancerous tissue. Not all types of cancer cells are affected, but the results are encouraging. They suggest that annona extracts may be a good complement to other cancer therapies.
A study published the following year, however, reached a very different conclusion. Potts et al. found that pawpaw extract is toxic to cortical neurons. That is to say: it kills brain cells. These findings support earlier observations that certain tropical populations exhibit high rates of atypical parkinsonism—Parkinson’s-like symptoms that cannot be attributed to Parkinson’s disease. A study of patients in Guadeloupe found exceptionally high rates of atypical parkinsonism. Soursop grows all over the island, and the authors speculated that an acetogenin called annonacin was one possible cause. By administering annonacin to rats, they were able to produce the same kinds of brain lesions they’d seen in autopsies of human patients.
There are lots of vendors at the Pinecrest farmers’ market who claim to have discovered a cure for cancer. Cancer-curing powders, teas, and foods are available at table after table: gluten-free baked goods cure cancer; Paleo granola cures cancer; fermented foods cure cancer. The general philosophy here is that cancer is a disease of civilization—a disease caused by plastics, food additives, hormones, and synthetic pesticides—and therefore ultimately an unnatural event that can be avoided by embracing natural remedies and organic produce. To some extent I think this must be true. Lots of synthetic chemicals turn out to be carcinogenic, and the plant kingdom is indeed full of miraculous medicines. Quinine changed the world. So did aspirin, in a different way. All kinds of plant-derived medicines have made life better for all kinds of people with all kinds of problems. It is a near-certainty that medicinal plants of great significance still await discovery.
But it’s also true—and we should try not to lose sight of this fact—that nature is full of poison. There is nothing inherently good about a natural remedy. Castor beans are the source of castor oil, which is an ingredient in many pharmaceutical products and is often said to have cancer-curing properties of its own, but it’s also the source of ricin, a deadly poison. Delicious organic chickpeas are neurotoxic if you eat enough of them.
The troubling thing is that it isn’t easy to distinguish poison from medicine. Sometimes it’s a matter of dosage: a little ibuprofen and you feel great; a lot of ibuprofen and you’re dead. Sometimes it’s a matter of balancing inevitable side effects with putative benefits. So even though we can hope that modern medicine will discover whether annonacin is a poison or a cancer drug, the answer isn’t likely to be that simple. Annonacin is a cytotoxin, but so are chemotherapy drugs. In fact this is the purpose of a chemotherapy drug—they are drugs that kill cells. Ideally, they kill cancer cells, but they also kill other cells, and the hope is simply that because cancer cells are growing quickly, they’ll absorb more of the poison than normal cells.
Having a body is tough, and having a mind is tough, and having both is especially tough. If you’re sick, I think you should skip the farmers’ market and go to the doctor. But then again, who knows? If you have access to an Amazonian shaman, maybe have a chat with him as well.
Aaron Thier is the author of The Ghost Apple. His new novel, Mr. Eternity, will be published in 2016.