I had always been told that the reason to avoid eating carambola (star fruit) if you have end stage renal disease and need dialysis is because of the oxalate. Yet many Hawaiian plants, such as taro, are rich in oxalates to the point they are inedible until well soaked or cooked to partly remove the soluble portion of their oxalic acid. Why is the warning only for star fruit, which contains so little oxalate (yet much more than average for a fruit) that it is easy to eat fresh from the tree?
The answer seems to be that it is not the oxalate, but a neurotoxin, caramboxin, which is normally rapidly removed by the kidneys, but hangs around in the body with kidney failure enough to penetrate into the brain, where it causes encephalopathy with confusion, nausea, vomiting, hiccups (hiccups are uncommon with other encephalopathies but are seen in about 80% of cases of caramboxin encephalopathy), and in extreme cases seizures or coma, rarely death. So enjoy starfruit--unless you are on dialysis for kidney failure!
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ABSTRACT
Garcia-Cairasco, N., Moyses-Neto, M., Del Vecchio, F., Oliveira, J. A. C., dos Santos, F. L., Castro, O. W., Arisi, G. M., Dantas, M., Carolino, R. O. G., Coutinho-Netto, J., Dagostin, A. L. A., Rodrigues, M. C. A., Leão, R. M., Quintiliano, S. A. P., Silva, L. F., Gobbo-Neto, L. and Lopes, N. P.
Elucidating the Neurotoxicity of the Star Fruit.
Angew. Chem. Int. Ed., 52: 13067–13070 (2013).
doi: 10.1002/anie.201305382
Caramboxin: Patients suffering from chronic kidney disease are frequently intoxicated after ingesting star fruit. The main symptoms of this intoxication are named in the picture. Bioguided chemical procedures resulted in the discovery of caramboxin, which is a phenylalanine-like molecule that is responsible for intoxication. Functional experiments in vivo and in vitro point towards the glutamatergic ionotropic molecular actions of caramboxin, which explains its convulsant and neurodegenerative properties.
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