Is Star Fruit A Kidney Poison? (Dr JB Lim Explains)

The blogger’s note: There was an email circulated in the internet a few years ago regarding a 66-year-old Malaysian who has been suffering from kidney ailment fell into coma after eating star fruits. There was a statement that said “all it takes is one fruit or 100ml of its juice and the ordinarily harmless star fruit transforms poison in a matter of hours for kidney patients”, and another from a Universiti Malaya Medical Centre consultant nephrologist who said that star fruits contain a neurotoxin which is not present in other fruits and it affects the brain and nerves. Is star fruit (Chinese: 杨桃; Malay: Belimbing) a kidney poison? Dr JB Lim explains as follows:

Monday, 23 April, 2012 10:32 PM

From: lim juboo

Dear all who asked,

Is Star Fruit Toxic?

Thank you for your enquiry.

No! no! no! Star fruit, botanically called carambola, is not a poisonous fruit as much as most fruits and vegetables like our Malaysian bayam, black tea (fermented and dried tea), leaves of rhubarb, spinach spinach, rhubarb, Brussels sprouts, broccoli, carrots, green peppers, cabbage, beets, kale, eggplant, okra (lady’s finger) squash, parsley, lettuce, just to name a few among many other Malaysian and tropical fruits and vegetables, are all not toxic. All of them too contain oxalic acid. It is not just star fruit that contains oxalic acid.

Unqualified Advice:

If any of you think that eating carambola is going to damage your kidneys because the oxalic acid in it will damage your kidneys, then you should also not eat any other fruits and vegetables I have mentioned here, because they all contain oxalic acid in fairly high content. Don’t act silly because all fruits and vegetables including star fruit are extremely good for health especially against most cancers and coronary heart disease.

If only people have studied and understand renal physiology they will realize how beautifully the kidneys work for them in clearing up almost all toxins, including oxalic acids provided their kidney functions are normal, and there is sufficient fluid (water) intake – at least 2.5 litres a day for a reference adult male of 65 kg in the tropics like Malaysia.

Renal function:

The status of kidney health can easily be measured by various renal function tests. Some examples are (very briefly in point form): .

• Plasma concentrations of the waste substances like creatinine and urea

• Electrolytes (potassium and sodium)

• Blood urea nitrogen (BUN)

• Creatinine clearance

• GFR (glomerular filtration rate)

• Presence of micro-albumin among others
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These tests are more than sufficient to determine renal function and status of renal physiology. They are more than adequate to determine whether or not a patient is suffering from any kidney disease or renal impairment.

If the kidneys are functioning normally, and the fluid intake (water being drunk and from food) is sufficient to excrete these toxins - intermediary and end metabolites (products of metabolism or waste products from food breakdown in the body by the liver and normal metabolic pathways) are adequate, there is absolutely no problem about eating star fruit or any kind of fruits and vegetables that contains oxalic acid, because all fruits and vegetables do contain this acid to varying degrees.

Oxalate Stones:

The only problem with oxalic acid is that it can combine with calcium in the blood to form insoluble calcium oxalate, and that can block the kidneys as oxalate renal stones and impair kidney functions. That is the only rational I can see about the risk of eating far too many star fruit without adequate water been drunk.

Else calcium oxalate which is slightly soluble in water is formed most of time when fruits (including star fruit) and vegetables are consumed. Just drink sufficient water, especially ‘soft water’ where calcium and limestone contents are low, and no renal calculi – oxalate or calcium can block the kidneys.

Notwithstanding what I have said, star fruit which has excessive oxalic acid, like our pasar pagi / malam bayam, rhubarb, kale, brinjal, lady’s finger (okra), cabbage, broccoli, salad, kangkong, and so on, do not ( I repeat do not) cause any kidney damage in healthy individuals with healthy and un-impaired kidneys physiology.
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Except:
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In patients who already have kidney failure or renal impairment are strongly advised not to eat star fruit because they cannot handle the (mild) toxicity of oxalic acid. This complicates clinical outcome in renal impaired patients. There are several published reports reported in Hong Kong and elsewhere of kidney patients dying because they consumed carambola (belimbing), but not in others with healthy kidneys. Please note these reports were only on renal-compromised patients who were already on dialysis.
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Other pathologies:
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In fact patients with renal failure are also advised (without going into the complicated technical discussion on dietary and renal physiology) to be on restricted diet low in potassium, sodium, phosphorus, protein and fluid intake.

All these are nutrients (except water) critically needed by the body everyday, yet if they are not adjusted, the breakdown of proteins in the diet or from the body – metabolites (example urea and creatinine) can accumulate in the body giving rise to excessive urea and nitrogenous waste products in the blood (uraemia). The clinical presentations we shall leave out.

Also, do not confuse uraemia with uricemia, or hyperuricemia, the latter is a build up of uric acid in the blood that may result in clinical gout.

Also, do not confuse another kidney disorder called proteinuria which is an excessive output of serum protein in the urine. Again we shall not go into the clinical features and pathology of these diseases as it is unnecessary.

We can see here even certain categories of food need to be restricted in renal diseases. It is not just star fruit alone that need to be avoided.

Why do people only target on star fruit alone when some very essential nutrients are also to be restricted on the professional advice of a dietician or a physician specializing in diet-related nephrology?
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Drug interaction

Carambola is an inhibitor of seven cytochrome P450 isoforms (cellular enzymes). These enzymes are crucial for the first order primary elimination of many medications as this fruit shortens the retention time and peak levels of some drugs in the body.

Thus, if a patient is on some of these medications such as statins (cholesterol-lowering drugs), and tranquilizers (example: benzodiazepines, and diazepam), consuming star fruit may lower the effectiveness of these drugs, and thus the dosage need to be tittered (dose adjustment) against the patient’s individual needs to enhance its clinical / pharmacological response to treat cardiovascular and psychiatric illness.
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Healthy individuals:

But for individuals with healthy renal clearance, belimbing is a nutritious fruit – with a very high content of various antioxidants, vitamin C, besides low in sugar and sodium both of which we should aim for to prevent the rising incidence of diabetes mellitus, hypertension and CVD in Malaysia.

Its antioxidant properties, especially against nitric oxides and singlet oxygen radicals as a prophylaxis against cancers are attributed to the rich source of primary and secondary polyphenolic antioxidants in carambola. This much we know.

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Anti-microbial Properties:

Moreover, this fruit also exhibited antimicrobial properties against E. coli, Klebsiella sp., Staphylococcus aureus, and Pseudomonas aeruginosa. All these are medically pathogenic organisms. Please note P. aeruginosa in particular, is potentially a very dangerous bacteria that affects principally the kidneys, urinary tract, lungs and skin.

Please note, I mentioned kidneys and urinary tract. Isn’t star fruit then good for the kidneys instead of damaging it? As all those ‘experts’ who told you star fruit is ‘damaging’ to the kidney, the very organ star fruit is trying to protect against this highly anti-biotic resistant bacteria. You get fatal septic shock, urinary tract, kidney, gastrointestinal infections if you are infected with Pseudomonas aeruginosa. It has very low antibiotic susceptibility, and there are only very few antibiotics left that effective against P. aeruginosa as shown in clinical practice and in lab assays (C & S).

Rubbish newspapers:

But there is hope from compounds from star fruit that is effective against kidney infection by P. aeruginosa. Is that just the opposite from what newspapers, ‘health’ magazines, e-mails, bogus health experts and unqualified people claim?

Newspapers are meant only for gullible people, but are used for wrapping left-over foods, kitchen wares, unwanted items, nasi lemak, and goring pisang by learned people. Open your knowledge.
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Neurotoxin:
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As far as belimbing containing a neurotoxin (nerve poison) as claimed by some, I do not know, as a search of all existing literatures published so far has not shown up any authentic work on this claim. It is highly unethical and unprofessional for me to support such claims including from doctors and ‘experts', and I do not care who they are. All I want is published peer-reviewed scientific papers, in reputable international journals. That’s all I believe. I don’t listen to ‘experts’.

In the absence of published literatures, I refrain from making any comment. Show me the published work and the toxicological data first – then we talk. Else shut up and talk less.

Seek Qualified Professional Advice:
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Don’t be an idiot to read newspapers, women’s and health magazines, Internet reports, e-mail mass circulars to believe in rubbish claims. Always, always seek the qualified and professional advice of a registered nutritionist or a dietician for advice concerning food, nutrition, including food toxicology for his / her expert and qualified opinion only.
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The Legal Practice of Nutrition:
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Please note carefully the practice of nutrition in this country is going to be controlled and legalized by an Act of Parliament as a registered profession like the practice of medicine, dentistry or pharmacy.

All nutritionists from recognized universities must soon be registered with the Ministry of Health (MOH) and they must have a registrable degree in nutrition before they can practice in Malaysia.
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Illegal:
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It is illegal to give false, bogus and unqualified advice to any person (example star fruits are damaging to the kidneys) unless they have a recognized degree in nutrition which must be registrable with the MOH. Even qualified and registered nutritionists will soon have to answer to the Disciplinary Board if they provide false claims, and their license to practice may be cancelled. Nutritionists also now need an Annual Practicing License (APL) with credit points to renew their APL.

Any person in this country giving unqualified nutrition advice to any person, whether via e-mail, Face book, websites, newspaper reports, in health magazines, or in any publications will soon be prosecuted under the Allied Health Act. The practice of nutrition is soon to be gazetted legally as a profession.

The Bill is now in its final reading in Parliament. Please note this.
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Street and Direct Selling ‘Nutritionists’

So don’t give illegal advice like ‘duck’s eggs soaked in apple vinegar is good for health’. There are far too many such ‘nutritionists’ in the streets these days that the Government needs to act.

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Jb lim (A Belimbing Eater)

(Food Tech in Food Safety and Quality Control), PhD (Med)

Former Research Food Toxicologist

Massachusetts Institute of Technology (MIT)