f295 Carambola

Related species: Bilimbi (Averrhoa bilimbi L.)

Food

A food, which may result in allergy symptoms in sensitised individuals.

Allergen Exposure

The fruit comes from a tree, which grows up to 12 metres. This tree has been cultivated in Southeast Asia and Malaysia for hundreds of years, and now is also found in many places in the New World, in appropriate climates. The fruit, ovate to ellipsoid and 6 to 13cm in length, has a yellowish or greenish, waxy, translucent skin. Slices cut in cross-section are star-shaped, with five corners. The flesh is yellow, translucent, crisp and very juicy. There may be up to 12 flat, thin, brown seeds. There are 2 distinct classes of carambola: the smaller, very sour type, richly flavoured, with more oxalic acid; and the larger, ‘sweet’ type, mild-flavoured, with less oxalic acid.

Ripe carambolas are eaten out of hand, sliced and served in salads, or used as garnish. Their juice is very popular in the East. They are also cooked in puddings, tarts, stews and curries. The sweeter type may be cooked green as a vegetable. They can serve as the main ingredient of sherbet, seasoning, jelly, or relish. The fruits may be stewed, dried, canned, pickled or candied.

Medicinally, the fruit is used against haemorrhages, fevers, diarrhoea, eye afflictions, eczema, and kidney, liver and bladder complaints. However, there are health risks from the oxalic acid in fully ripe carambolas: see under Other reactions below.

The acidic types of carambola are used to clean and polish metal, especially brass, as they dissolve tarnish and rust. The juice is also used as a stain remover. Unripe fruits serve as a mordant in dyeing.

Allergen Description 

No allergens from this food have yet been characterised.

No cross-reactivity has been reported to date.

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)