Overview

Star fruit (carambola) comes from tropical countries but is widely enjoyed throughout the world. This fruit has been recognised for its powerful health properties, which can also be used medicinally. Bright yellow in colour and with a unique shape, this fruit is full of antioxidants, vitamins and minerals as well as being high in fibre and low in calories. 

Star fruit has some profound health benefits including helping to lower your inflammation as well as balancing your blood glucose levels. This fruit can also lower your cholesterol levels which can have a great impact for your cardiovascular health and help prevent cardiovascular diseases. 

Amazingly, star fruit has also been found to help protect against infection as well as reducing tumour formation through its immune-boosting and medicinal effects.¹ However, despite the health benefits that star fruit holds, there has been some toxicity of star fruit discovered when eaten in high volumes or if you have pre-existing kidney problems. However, when eaten at safe levels, this fruit is sure to keep the immune system healthy. 

In this article, the immune-boosting effects of star fruit will be discussed in detail.

Vitamin C

Star fruit is full of vitamin C and one serving of star fruit holds over half of your daily recommended serving of this vitamin. Vitamin C levels are well known for being important for immune system health. This vitamin helps to improve both your innate and adaptive immune system which combat a wide range of infections. Your innate immune system is the first line of defence which is non-specific and tackles any infection fairly similarly whereas your adaptive immune system is specific to the type of infection that you have. 

Vitamin C also helps to improve immune cell proliferation following an infection as well as immune cell migration to the site of the infection. This enhances the immune response by allowing your immune system to build an army of immune cells whilst also improving how fast and efficiently your immune cells can travel to where they are needed.²

Vitamin C is also a known antioxidant which can help to locate and neutralise harmful chemicals called free radicals. Free radicals can be generated as by-products through normal cell functioning or through environmental agents such as smoking, poor diet, sunburn, or pollution. Free radicals can lead to extensive cell damage which can cause chronic inflammation. If not managed well, free radicals can cause DNA mutations which can eventually lead to cancer, this highlights the importance of having a diet rich in antioxidants.³

 Additionally, too much inflammation can negatively alter your immune response and lead to things such as asthma and other allergic responses. Luckily, starfruit is rich in many antioxidants which can help reduce chronic inflammation, more detail on the antioxidants found in starfruit will be covered later.¹

Vitamin A

Vitamin A is a crucial vitamin for the immune system as it helps to develop many immune cells that are important within the body. When you have an infection, vitamin A gets used up rapidly, leaving your vitamin A levels low and this can hinder your ability to fight an infection. This can increase your inflammation levels for unnecessary periods of time, having long-term effects on your health. This vitamin cannot be made within the body and therefore, we need to obtain it mainly through our diet. 

Your lymph nodes and spleen are lymphoid organs where your immune cells are activated and proliferate, and it has been found that these organs require vitamin A for immune cell proliferation. It was also found that those low in vitamin A had a higher level of premature immune cell death, hindering your immune response and prolonging infections.

Another way your body helps to protect you from infections is by producing layers of mucus within the lining of your intestinal tract, which vitamin A helps to produce. This helps to flush infections out of your intestinal tract and prevents them from entering your system.⁴ 

Antioxidants

Star fruit contains many antioxidants which have amazing benefits for your body. As mentioned above, the anti-inflammatory as well as the anti-cancer benefits of antioxidants make this fruit an amazing choice.

Polyphenols   

Polyphenols are a large family of antioxidative compounds that display an immunoregulatory function where they will help to prevent chronic or unnecessary inflammation. They do this through different mechanisms including cytokine modulation, which are proteins that can signal to the immune system when there is an infection and increase the inflammatory response. However, they can also send out anti-inflammatory signals which alert the immune system to stop reacting.⁵ 

Flavonoids 

Flavonoids are a type of phytochemical which hold many great benefits including antiviral, anti-cancer, anti-inflammatory and anti-oxidative. Flavonoids display anti-cancer effects through their ability to prevent rapid cell growth and division, potentially slowing or preventing the growth of cancerous cells. Flavonoids have been growing in popularity and becoming more attractive as some drugs which treat cancer now contain flavonoids due to their profound capabilities.⁶

Antioxidants and the immune system

Antioxidants have a wide range of functions within the body, including reducing damage from free radicals, reducing inflammation and enhancing the immune response. In normal conditions, the cell membranes on your immune cells are flexible which helps them to communicate with other immune cells, allowing them to respond to any invading infections. 

Free radicals can cause damage to immune cells and cause their membranes to become stiff and unable to communicate effectively, leading to your immune response becoming hindered. By consuming plenty of antioxidants, you will help to keep the communications between immune cells efficient and give your immune response the best chance at combatting the infection.⁷

Toxicity

Nephrotoxicity, the toxicity of your kidneys and neurotoxicity, the toxicity of the brain and nerve cells, has been found to occur following the consumption of star fruit. Those with kidney diseases are not recommended to eat star fruit as it can cause further complications.¹

Toxicity can be caused due to the Oxalic acid and Caramboxin (a neurotoxin) content which have been reported to cause lethal toxicity after an oral dose of 15 grams. Oxalic acid can cause calcium to deposit in the kidney tubules which can lead to blockage and haemodialysis, where your kidneys can no longer filter nutrients from your blood. Neurotoxicity has also been reported with oxalic acid and Caramboxin. In extreme cases, these compounds have been known to lead to the overactivation of the brain, leading to seizures. This is due to these chemicals blocking the inhibitory receptor of the brain which causes excessive activity.^8,9

Generally, if you have a healthy and balanced lifestyle and consume star fruit in moderation, this fruit can have some great health benefits. However, if you suffer from kidney problems or are on medication for your kidneys, it is recommended that you do not consume star fruit, or speak to a health professional before you do. 

Incorporating star fruit into the diet

Star fruit is quite a small fruit with a lovely sweet and tangy taste and can be enjoyed in a range of different ways. When sliced, this fruit has a star shape which can add a nice touch to a fruit salad. Additionally, star fruit can be used in smoothies to add a healthy boost and a fresh and tangy taste. Star fruit has also been enjoyed in baked goods which add a surprising freshness to muffins or cakes. Conversely, star fruit can be made into chutneys to be enjoyed as an addition to a savoury dish.

Summary

Starfruit is packed full of antioxidants, vitamins and minerals which can give you amazing and powerful health benefits including anti-inflammatory and anti-cancer effects. Vitamin C is a powerful antioxidant which can prevent cellular damage by free radicals. This vitamin can also help to improve the immune response by helping your immune cells to grow and respond rapidly. Star fruit has amazing health benefits, however, those on medication for their kidneys should steer clear of this fruit as it can cause problems.