Star fruit (also known as carambola) is a tropical fruit that traditionally comes from a tree (Averrhoa carambola) native to Sri Lanka and the Moluccas (also known as the Spice Islands), an archipelago in Indonesia. It is now grown in Florida and Hawaii, as well as in Southeast Asia and Malaysia. The name star fruit comes from the fact that when sliced, the cross section has the shape of a five-pointed star.
Star fruit can be yellow to green with a complex flavor that may be tart or sweet, combining flavors of pineapples and lemons.
If you have no kidney problems, you can eat all the star fruit you want - it has no effect on healthy kidneys. But if your kidney function is impaired, eating star fruit can be very dangerous, even deadly. Symptoms of "star fruit intoxication" include persistent hiccups, nausea, vomiting, agitation, insomnia, mental confusion and convulsions that occur within one to five hours of eating the fruit.
The problem seems to be the high levels of oxalic acid (or oxalate) in this fruit that can accumulate in weakened kidneys. But since kidney patients don't seem to have problems eating other oxalate-rich foods (such as spinach), Brazilian researchers who have been studying the reaction suggest that another, unidentified substance toxic to nerves is the real culprit. Whatever this toxin may be, people with healthy kidneys have no problem excreting it while those with impaired kidney function run into trouble with the combination of the unknown toxin and oxalate. The only way to deal with star fruit intoxication is prompt dialysis – so anyone who does have kidney problems and develops hiccups, vomiting or other symptoms after eating star fruit should get immediate medical attention.
Star fruit intoxication can develop in patients with kidney failure after eating as little as one half of a fruit or drinking less than eight ounces of star fruit juice. In one case, a patient with impaired kidney function died after eating just a single star fruit.
Andrew Weil, M.D.