IgE-mediated reactions
Anecdotal evidence suggests that carambola may induce symptoms of food allergy in sensitised individuals; however, no studies have been reported to date.
Other reactions
Six patients in a dialysis programme were apparently intoxicated by ingestion of 2-3 fruits or 150-200ml of the juice, and developed a variety of symptoms – ranging from insomnia and hiccups, to agitation and mental confusion – which in one case resulted in death. The effects were believed to come from an excitatory neurotoxin in the fruit. (1) A recent study concluded that oxalate is a main contributor to carambola neurotoxicity, rather than an excitatory neurotoxin. Carambola contains a large quantity of oxalate, which can induce depression of cerebral function and cause seizures. (2, 3)
There have been other reports of nausea, vomiting, intractable hiccups, severe encephalopathy along with mental confusion, disorientation, agitation, and seizures, and occasional fatal outcomes in uraemic patients after ingestion of star fruit. (4, 5, 6, 7, 8, 9, 10, 11)
A group of 7 patients is described, who developed symptoms including hiccup, confusion, vomiting, impaired consciousness, muscle twitching and hyperkalaemia shortly after ingestion of star fruit. Symptoms of most patients resolved after intensified dialysis or spontaneously, and no mortality was observed. (4)
Further support for oxalate as the cause of the adverse effects seen is reported in 2 other cases, where patients developed nausea, vomiting, abdominal pain, and backache within hours of ingesting large quantities of sour carambola juice; followed by acute renal failure. Both patients needed haemodialysis for oliguric acute renal failure, and pathologic examinations showed typical changes of acute oxalate nephropathy. Renal function recovered 4 weeks later without specific treatment. Sour carambola juice is a popular beverage in Taiwan, but commercial juice is usually prepared by pickling and dilution processes that reduce oxalate content markedly, whereas pure fresh or semi-fresh juice for traditional remedies (as had been used in the above cases) contains high quantities of oxalate. An empty stomach and a dehydrated state may pose additional risks for development of renal injury. (12)
In patients on dialysis, consumption of carambola can lead to alterations of consciousness, as described in a patient with underlying chronic kidney disease who developed a rapid increase in serum creatinine and oxalate nephropathy after chronic ingestion of carambola juice; there was no overt neurotoxicity. The decline in renal function was not fully reversible after stoppage. (13) However, toxicity may occur after a very short duration of ingestion, and may also result in epilepsy: an 84-year-old Asian woman with hypertension and chronic renal failure developed incoherent speech, followed by intermittent interruptions of consciousness, and then status epilepticus, after ingesting a single carambola fruit each day for 3 days. (14) Non-convulsive status epilepticus has also been reported in chronic renal failure patients on maintenance dialysis therapy after they have eaten star fruit. (15)
Carambola contains agents that inhibit cytochrome P450 3A4 (CYP3A4), which is the most important enzyme in drug metabolism. Carambola interacts with drugs. (16)
