Is starfruit something you need to avoid with Polycystic Kidney Disease? The short answer is yes.  The bigger question is... WHY?  Keep reading to learn more about starfruit, the toxins it contains that aren't kidney-friendly, and how oxalates factor in. 

Starfruit

Starfruit, also known as carambola, is a sweet and sometimes tangy fruit with a citrus-like flavor. It is native to tropical regions of Southeast Asia and has recently gained popularity around the globe thanks to its taste and fun shape. Luckily, it can also be found in grocery stores worldwide.  

Starfruit is shaped like a star when sliced up, hence its name! It can be yellow or somewhat green, depending on the specific variety. For most people, starfruit can be a nutritious addition to their diet. It is rich in Vitamin C, fiber, and antioxidants. 

In tropical countries, where starfruit is readily available, its juice and extract are commonly used as an herbal remedy to help lower glucose levels with Diabetes. 

The Kidney Connection

Consuming starfruit, however, can have life-threatening consequences if you have kidney damage or lower kidney function, a lower eGFR. This unfortunately includes anyone with Polycystic Kidney Disease.  

Starfruit contains two dangerous toxins. The first is Caramboxin, which can negatively affect the brain and nervous system.  The second toxin is Oxalic Acid, which is dangerous to the kidneys at high concentrations.

Your kidneys are the body’s filter, keeping what your body needs and filtering out excess waste and fluids.  When kidneys aren’t filtering at full function or are damaged, caramboxin and oxalate toxins are not adequately eliminated. Instead, they can build up in the body and are transported to the brain and kidneys where they can cause substantial damage.

Dangerous Toxins

Let's take a closer look at the two main toxins in Starfruit.  So you will have a better understanding of how it isn't PKD-friendly.

Caramboxin Toxin

Caramboxin is a neurotoxin, meaning it affects the brain and nervous system. It can cause seizures and nerve damage, and at high levels can be fatal.  Starfruit is the only food that naturally contains the caramboxin toxin. 

One of the first signs of caramboxin intoxication is uncontrollable hiccups.  Other symptoms include muscle weakness, seizures, agitation, confusion, and even a coma. 

Oxalic Acid Toxin

Oxalic Acids, commonly called oxalates, are nephrotoxic at high concentrations, meaning they can injure and negatively affect the kidneys.  

Starfruit is a dense source of oxalates.  Just ½ cup of fresh fruit has over 230 mg of oxalates and 4 oz starfruit juice can contain up to 800 mg of oxalates.  To put this in perspective, a common recommendation for people who form calcium oxalate stones is limiting oxalate intake to < 100 mg daily.  

Small Amounts, Big Kidney Risks

Additional kidney injury, in people who have kidney disease, following starfruit consumption is well documented. This injury is caused by blockage of the kidney’s filtering tubules by oxalate crystals and the death of some of the kidney’s cells.  

Side effects of kidney injury related to starfruit consumption, and a heavy oxalate load, can include inflammation, kidney stones, kidney damage, and toxicity, and can even lead to permanent loss of kidney function.

A “large amount” of starfruit, looking at published research and case studies, is considered 3-4 of the whole fruits or ½ cup of juice.  Just a small amount of the fruit or juice can lead to big kidney concerns! 

It is crucial to emphasize that we're not talking about large amounts here. The risk factors for issues with both toxins are noteworthy, especially for those consuming starfruit on an empty stomach, when dehydrated, or for individuals with pre-existing altered kidney function or disease. 

Bottomline

If you have Polycystic Kidney Disease (PKD) avoid starfruit. The risk outweighs any potential benefits even if your kidney function, as measured by GFR, appears normal. 

You can enjoy plenty of other fruits without the risk of direct harm to your brain and/or kidneys.  

Have you checked out The PKD Dietitian Podcast?  Listen now to the episode on Starfruit and PKD.  Make sure to hit the subscribe button so you never miss an episode.

Happy & Healthy Eating,

Diana, The PKD Dietitian