What are side effects of star fruit or kamranga?

Star fruit (Averrhoa carambola)  which is also known as Kamranga is a refreshing touch and consumed for health benefit. It is also used for making Chatanee in household preparation. This fruit has both nutritional as well as medicinal uses. In Sri Lanka, traditional use of kamranga is common for conditions such as diabetes mellitus due to its hypoglycaemic effects. But people with impaired kidney function (oxalate nephrotoxicity), it can be deadly and may cause sudden kidney shutdown. It may also affect healthy persons who consume a certain amount of juice at a time in an empty stomach with raw form.

Star fruit contains oxalate that may accumulate in kidney if taken excessively, especially when taken in raw form and in empty stomach. As low as 300-350 ml of Kamranga juice may affect even a healthy individual. So consuming excessive amount of kamranga juice at a time is definitely give adverse health effect even in normal body.

Star fruit contains a type of poison or toxin called caramboxin (CBX, C₁₁H₁₃NO₆). Caramboxin is a certain types of neurotoxin. People with healthy kidney can remove it from the body, but in the case of a patient with chronic kidney disease (CKD), it accumulates in the body and goes to the brain with the blood.

When renal function or kidney function is abnormal there is an elevation of caramboxin in the central nervous system that results in neurological symptoms such as hiccups, nausea, mental instability, seizure, coma and even death. Posible interaction between caramboxin and oxalic acid in star fruit leading to both neurotoxic as well as nephrotoxic effects.

IUPAC name2-Carboxy-3-hydroxy-5-methoxy-L-phenylalanine

Cases with start fruit consumption

1. 56 years female diabetic patient having no renal function problem. But after consuming excessive amount juice at a time developed acute kidney injury (AKI).
2. 60 years male patient also having diabetes problem observed with acute on chronic renal failure. He was consuming star fruit juice since 2-3 years. But before hospitalisation he was consuming more fruits with a short duration. (See details). Both patients recovered over 2 weeks without any haemodialysis.   (Source: NCBI)