Star fruit, known locally as มะเฟือง, is a familiar presence in Thai markets and home gardens, prized for its tart-sweet flavour, decorative star-shaped slices, and thirst-quenching crunch. In recent years, this glossy tropical fruit has attracted global attention not just for its unique taste but also for its nutritional punch and therapeutic potential. However, alongside its growing popularity, evidence has emerged of serious health risks for certain vulnerable groups. Understanding the full story of star fruit is essential for Thai consumers who wish to enjoy its benefits safely.
From a nutritional perspective, star fruit is a low-calorie food packed with vitamins, minerals, and a host of valuable plant compounds. A medium-sized star fruit (about 91 grams) delivers just 28 calories, but provides 3 grams of fiber, 1 gram of protein, and more than half the recommended daily vitamin C content, along with smaller amounts of folate, vitamin B5, copper, potassium, and magnesium. The fruit is particularly rich in antioxidants, such as vitamin C, gallic acid, epicatechin, and quercetin, all of which help neutralise harmful free radicals in the body and may lower the risk of certain chronic diseases. Animal studies have suggested that these compounds may help reduce inflammation, improve cholesterol profiles, and even diminish risk factors for fatty liver disease, though robust human studies are still needed to confirm these effects (Healthline).
The role of star fruit in traditional medicine is also well established in Thailand and across Asia. Thai traditional healers and households have used it as a remedy for sore throat, cough, fever, and as a digestive aid. Scientific reviews confirm that extracts from the fruit, leaves, and roots contain saponins, flavonoids, alkaloids, and tannins, contributing to its anti-inflammatory, antimicrobial, antiulcer, and antioxidant properties (PMC5357571). For instance, studies on mice have shown reduced skin inflammation when treated with star fruit extract, and some laboratory research indicates potential activity against bacteria like Staphylococcus aureus and E. coli.
Recent research involving elderly participants in northern Thailand found that consuming star fruit juice (100g twice daily for a month) led to significant improvements in antioxidant status and a healthier blood lipid profile, with higher HDL (“good” cholesterol) and lower LDL (“bad” cholesterol) levels (PMC5012612). Participants also showed reduced markers of oxidative stress and inflammation—important factors in aging and chronic diseases such as hypertension and diabetes. Notably, the study found no short-term adverse effects on liver or kidney function in healthy elderly people, though the authors caution that long-term safety and oxalate levels were not evaluated.
However, for all its benefits, star fruit carries a hidden danger that most consumers—especially in Thailand’s aging society—may not fully appreciate. The most serious risk lies in its extremely high oxalate content, particularly in the sour varieties. Oxalate is a naturally occurring compound that, in excess, can cause severe kidney problems, especially in people with underlying kidney disease or reduced kidney function. People with kidney issues are unable to efficiently excrete oxalate and another star fruit compound, caramboxin, both of which can accumulate and cause toxicity. Clinical cases have shown that even a small amount of star fruit—sometimes just half a fruit—can trigger acute kidney injury (with symptoms such as vomiting, hiccups, confusion, seizures and even coma) in those with chronic kidney disease (BMC Nephrol). In people with normal kidney function, very high consumption (for example, four or more fruits or large amounts of pure juice) has also led to cases of acute oxalate nephropathy, sometimes requiring hospitalisation and dialysis. Fortunately, most people with healthy kidneys recover fully, but the cases underline the importance of moderation and awareness.
The danger for kidney patients is compounded by the fact that star fruit is sometimes recommended in natural medicine for controlling blood sugar in diabetes—a group already at higher risk of kidney problems, and thus potentially more susceptible to star fruit toxicity. In a regional context, there have even been local case reports where doctors attributed kidney injury to frequent consumption of star fruit as a home health remedy. Medical professionals advise that anyone with diabetes, kidney disease, or those receiving dialysis should absolutely avoid star fruit and its juice, an urgent message that deserves more outreach in Thailand’s health promotion programmes.
Apart from oxalate toxicity, star fruit may also interact with conventional medications. Some research suggests that compounds in the fruit can inhibit certain liver enzymes, particularly those in the cytochrome P450 family (such as CYP3A), which are responsible for breaking down a wide range of common prescription drugs (PubMed). This means star fruit might alter drug levels in the body, potentially leading to harmful side effects or reducing the effectiveness of medications, much in the way that grapefruit is known to do. If you are taking any medications—especially for chronic conditions—check with your physician before introducing star fruit to your diet.
For healthy individuals, guidelines based on Thai and international scientific sources recommend that star fruit can be enjoyed safely as part of a diverse, balanced diet and in moderate amounts—one or two fruits per day, preferably accompanied by a variety of other fruits and vegetables as promoted by the WHO. Pregnant and breastfeeding women, children, people with a history of kidney stones, and older adults should use extra caution or consult a healthcare provider. It is also wise to avoid consuming undiluted sour star fruit juice in high quantities or on an empty stomach, as these situations are linked to a higher risk of absorbing oxalate. As with all fruits, washing thoroughly before consumption can help reduce potential pesticide or bacterial contaminants. Because cases have been reported where families made home-prepared star fruit drinks or pickles using large quantities at once, educating the public about safe preparation and moderation is particularly important.
Star fruit’s place in Thai culture extends beyond nutrition; it is a living symbol in seasonal festivals, home gardens, and even folklore, where its star-shaped slices are seen as bringing good luck. However, as Thailand becomes more urban and chronic diseases become prevalent, traditional beliefs about natural foods need updating with the latest medical knowledge. There is a growing imperative for Thai health authorities and educators to raise public awareness—especially among high-risk groups such as the elderly and those with kidney or metabolic diseases—about the possibility of life-threatening adverse effects from a seemingly innocuous local fruit.
Looking to the future, researchers are optimistic about unlocking star fruit’s full therapeutic potential, perhaps even through selective breeding or genetic modification to reduce oxalate and caramboxin content (PMC5357571). With advances in biotechnology and deeper research into its antioxidant, anti-inflammatory, and potential anticancer compounds, star fruit—or improved hybrids—could take on new significance in preventive medicine and nutrition, not just for Thailand but for tropical countries worldwide.
In conclusion, star fruit (มะเฟือง) offers a wealth of health-promoting nutrients and antioxidants, which can support cardiovascular health, enhance immunity, and potentially help control inflammation and blood fats when consumed in moderation by healthy individuals. However, it poses a severe risk of acute toxicity for anyone with reduced kidney function, those prone to kidney stones, and possibly diabetics taking the fruit as a traditional remedy. Consumption should be strictly avoided by these groups and approached with caution for everyone taking prescription medication. The key lesson for Thai consumers is to embrace moderation, variety, and informed choices—consult your healthcare provider if you have any underlying health issues, avoid untested medical advice from online sources, and share new knowledge with family and friends to ensure that Thailand’s beloved star fruit remains a safe and beneficial part of our dietary tradition.
Sources:
- Nutritional, Medicinal and Toxicological Attributes of Star-Fruits (Averrhoa carambola L.): A Review
- Star fruit nephrotoxicity: a case series and literature review
- A preliminary study on the effects of star fruit consumption on antioxidant and lipid status in elderly Thai individuals
- Star Fruit: Benefits, Risks, and How to Eat It (Healthline)
- Transient inhibition of cyp3a in rats by star fruit juice (PubMed)