This summer I’ve been taking care of a friend’s garden. She calls it her survival garden, as it surely would sustain her family if they ever needed it. Every week has delighted us with a new harvest: mango, amaranth, spinach, apples, papaya, banana, grapefruit, oranges, kale, taro, ginger, garlic, pole beans and tomatoes.
September doesn’t disappoint, bringing avocados, tangerines, pomegranates and star fruit.
I love meandering through the garden, examining the plants as they grow from seed to fruits, vegetables, legumes and grains. One of the most striking is the star fruit (Averrhoa carambola) with its characteristic shape, vibrant yellow color and fresh, gently sweet taste.
This bright yellow fruit has caught the eye of another group of people: scientists. Since 1993 star fruit has been the subject of intense scrutiny and research, due to the fact that distinct clusters of people worldwide exhibited signs of illness after ingesting the fruit or its juice. Symptoms included hiccups, as well as more serious neurological issues.
The one common thread these people shared is kidney disease, either previously diagnosed or undetected before the episode. Oxalic acid was blamed for these health disasters, as it is a key component to kidney stones, making the connection to kidney disease plausible. It was first believed that star fruit was the cause of these acute kidney injuries and chronic kidney diseases, flooding the kidneys with oxalic acid that people with diminished kidney function couldn’t filter.
However, some scientists questioned this since commonly eaten foods that contain up to twice as much oxalic acid as star fruit do not cause the same dangerous symptoms. These included parsley, chives, amaranth, spinach, beet leaves, carrots, taro leaves, almonds, radishes, collards, rhubarb and monstera fruit.
Recently, in 2015, after more research by the University of Sao Paulo, Brazil, a neurotoxin suspected to be responsible for the neurological symptoms was named caramboxin after the star fruit’s botanical name, carambola. Experiments showed that it affects the function of an important neurotransmitter, glutamate, causing undesired effects of the central nervous system.
Upon deeper study they found that the most common symptom was hiccups. More severe neurological symptoms, such as confusion and seizures had the worst prognosis, ending in death for about 30 percent of people with kidney impairment. Dialysis was the treatment used in over half of those in the study. All of the people with normal kidney function recovered. In those with kidney impairment, less than one star fruit was consumed while those with no kidney problems were able to consume more before symptoms occurred. In both groups, toxicity was worse when it was eaten on an empty stomach or when the person was dehydrated.
So, can I eat star fruit, you ask? Whether you simply enjoy star fruit for its fun star-like shape or its crisp taste, or have read or been told that it is a health food for a particular ailment, this is a very wise question. It is solidly shown that people with any impaired kidney function are at higher risk of star fruit toxicity or even death. Any diagnosis of kidney disease is reason for preventative measures.
Undetected or undiagnosed kidney disease is also a risk. In addition there have been cases of acute kidney injury in people with no history of kidney disease who had eaten large amounts of star fruit. For a definitive answer, a consultation with a health care provider is the best plan, and in the meantime, enjoy the rest of late summer’s bounty that is healthful for you, and admire the star fruit from afar.