Health Benefits Of Star Fruit

What is star fruit?

Star fruit (Averrhoa carambola) is a tropical fruit native to Southeast Asia. It is also called carambola or five fingers. It gets its name from the star-shaped slices it has when cut open.^1,2

Star fruits are golden yellow or yellow-orange and have 5-6 ridges. They’re fleshy, juicy, crunchy, and have an acidic, sweet-tart flavour. They are usually available from March to August.^2,3

Star fruits are popular exotic fruits extensively grown in southern China, India, and northern South America. They have high commercial value due to their many nutrients and health benefits.²

The fruits, leaves, roots, and flowers of star fruits have been traditionally used as a natural medicine in China, India, Malaysia, and Brazil to treat:

• Diabetes and its complications
• Heart diseases like high blood pressure and angina
• Fevers, coughing, vomiting, and headaches
• Chickenpox and ringworm
• Joint pain and hangovers
• Urinary system disorders²

Ripe star fruits and star fruit juice have been used as a digestive, tonic, and food supplement to improve appetite and to treat haemorrhoids, eczema, and diarrhoea.²

The antioxidant potential of star fruit

Star fruits have high antioxidant capacity since they are a rich source of natural antioxidants like vitamin C, gallic acid, and beta-carotene. They also have a higher polyphenol and flavonoid content than other tropical fruits, further boosting their antioxidant potential.^2,3,4

Bioactive components of star fruit 

The bioactive phytochemicals (compounds found in plants) of star fruits are responsible for their health benefits. Researchers have isolated 132 of these compounds from the fruits, leaves, bark, flowers, and roots of star fruit trees.² The ones present in fresh ripe star fruits are:

• Flavonoids: These have antioxidant, anti-inflammatory, anti-cancer, and anti-diabetic effects. They also promote brain and heart health^1,2,4,5
• Phenolic acids: These have antioxidant, anti-inflammatory, and anti-microbial properties. They reduce the risk of cancer, diabetes, and cardiovascular disease^1,2,4,6
• Proanthocyanidins: These have antioxidant and anti-inflammatory effects. They also prevent and treat heart disease, diabetes, obesity, and cancer^2,4,7
• Saponins: These have antioxidant, anti-inflammatory, and anti-cancer properties. They help reduce cholesterol and blood sugar levels^2,4,8

Besides these bioactive components, star fruits contain terpenes and organic acids like citric, oxaloacetic, malic, fumaric, tartaric, α-ketoglutaric, succinic, and oxalic acids. Terpenes and proanthocyanidins are responsible for the taste and colour of star fruits. However, it’s unclear if the former has any health benefits.^1,2,3

How to incorporate star fruits into your diet

Star fruits are best eaten ripe. Ripe star fruits are distinguished by their yellow colour and sweetish-sour taste. On the other hand, unripe star fruits are green and have a sour or bitter taste.^1,3 Besides eating star fruits on their own, they can also be:

• Added to fruit salads and fruit platters along with other tropical fruits like dragon fruit, kiwi, and papaya
• Used as a garnish for beverages and cocktails
• Juiced or pureed into smoothies or drinks
• Cooked or braised with spices, limes, or peppers in meat or seafood cuisines
• Added to curries and stews
• Used in dips, sauces, and puddings 
• Baked in cakes and pies^1,2,4

You can also try commercial star fruit products like jellies, jams, pickles, preserves, or ice creams.^1,4

Health benefits of star fruit

Due to limited studies on the health benefits of star fruits in humans, here are potential health benefits of star fruits as seen in animal and in-vitro studies:

• Prevents cardiovascular disease (CVD): Fresh star fruit reduces high blood pressure and prevents high cholesterol, a risk factor for CVD. Star fruit extract maintains heart health by mitigating inflammation, necrosis (cell death), and fibrosis (scarring) of heart tissues^2,4
• Antioxidant activity: Being a rich source of natural antioxidants, star fruits neutralise free radicals, preventing oxidative stress. A study in elderly adults showed that drinking star fruit juice increased antioxidant capacity and levels of vitamins A and C^,4
• Anti-inflammatory activity: Animal and human studies show that both fresh star fruit and star fruit juice reduce inflammation. A study in elderly adults revealed that consuming 100g of star fruit juice for 4 weeks decreased inflammation by inhibiting inflammatory mediators^2,4 
• Prevents diabetes: Star fruits help prevent and treat diabetes by lowering glucose (blood sugar) levels, increasing insulin levels, and slowing down the conversion of starch to glucose. These effects were observed when fresh star fruit, star fruit extract, and star fruit powder were consumed^2,4
• Reduces cholesterol levels: Star fruits improve lipid (fat) profiles by lowering LDL cholesterol (‘bad cholesterol’) levels, increasing HDL cholesterol (‘good cholesterol’) levels, and decreasing triglyceride levels. They can help treat high cholesterol as they aid in the excretion of lipids and cholesterol^2,4 
• Prevents cancer: Star fruits reduce the number of tumours and tumour size in animal models. They also decrease the amount of cancer cells in human and animal cancer cells. Additionally, they may help prevent cancer by reducing oxidative stress on healthy cells^2,4
• Helps with weight loss: Star fruits prevent weight gain as they are low-calorie and low-fat. Moreover, their fibre content delays stomach emptying and increases the feeling of fullness, thereby preventing the intake of more calories^2,4 
• Promotes liver health: Star fruits promote liver health by reducing lipid oxidation and cholesterol levels in the liver. They also enhance the levels of enzymes that protect liver cells from free radicals. Additionally, they can prevent and treat liver cancer and fatty liver disease^2,4
• Prevents microbial infections: Fresh fruit, fruit juice, and extract of star fruit have antibacterial and antifungal properties. Star fruit extracts have greater efficacy than the other two against various strains of bacteria. One study revealed that bacterial strains like E. coli and S. typhi were more sensitive to the extract than standard antibiotics^2,4,9

The health benefits of star fruits are not restricted to the fruit alone. The peel, bark, and leaves also have beneficial effects. However, they’ve only been observed in animal models and in-vitro studies. Hence, more human trials should be conducted as star fruits have massive potential as a therapeutic agent.^2,4 

Nutritional facts

Star fruits are a good source of many macronutrients and micronutrients. They contain:

• Carbohydrates: 

100 g of fresh starfruit contains 6.73 g of total carbohydrates (including 3.98 g of sugar). The sugar content of ripe star fruits comprises:

• Fructose (38-48%)
• Glucose (21-25%)
• Sorbitol (2.4-10.5%)

Carbohydrates include simple sugars, starch, and fibre. They provide the body with energy when broken down into glucose.^1,2,4

• Dietary fibre:

100g of fresh star fruit contains 2.8 g of dietary fibre. It is composed of:

• Insoluble fibre: Cellulose (60%) and hemicellulose (27%) 
• Soluble fibre: Pectin (13%)

Both fibre types reduce cholesterol levels, control blood sugar, relieve constipation, and aid in weight loss.^2,4

• Vitamins:

Star fruits are a rich source of plenty of vitamins. They contain:

• Vitamin B1
• Vitamin B2
• Vitamin B3
• Vitamin B5
• Vitamin B6
• Vitamin C
• Pro-vitamin A
• Folate
• Vitamin E

1 cup of star fruits (132 g) provides 50% of the daily value (%DV) of vitamin C. It’s a potent antioxidant that neutralises free radicals and prevents oxidative stress. It also helps with:

• Collagen formation (a protein required to make skin, blood vessels, ligaments, and tendons)
• Wound healing and immunity boosting
• Repair and maintenance of the bones, teeth, and cartilage
• Lowering the risk of cancer, cardiovascular disease, and other disorders caused by oxidative damage^2,3,4

• Minerals:

1 cup of star fruits (132 g) contains:

• 20% DV of copper
• 4% DV of potassium
• 3% DV of magnesium

Copper helps with iron absorption, red blood cell formation, maintaining the immune system, and keeping bones, blood vessels, and nerves healthy. 

Magnesium and potassium are essential for normal body functioning. They’re needed for everything from muscle contraction, nerve transmission, and maintenance of a healthy immune system to the normal functioning of the heart and kidneys. 

Besides these minerals, star fruits also provide small quantities of calcium, sodium, phosphorous, iron, zinc, selenium, and manganese.^2,3,4

Other nutrition facts about star fruit:

• 100 g of star fruit contains 31 kcal and 0.33 g of fat^1,2,3
• Freeze-dried star fruits contain more carbohydrates (24.22 g) and dietary fibre (7.89 g) than fresh star fruit³
• 1 cup of star fruits (132 g) provides:
  • 1% DV of Vitamin B6 and Vitamin E
  • 2% DV of Vitamin B1 and B2
  • 3% DV of Vitamin B3 and Pro-vitamin A
  • 4% DV of folate (Vitamin B9)
  • 10% Vitamin B5
• The calcium content of star fruits is higher when they are ripe⁴

Side effects and other concerns

Despite its many health benefits, eating star fruits has its drawbacks. The side effects of star fruit consumption include:

• Gastrointestinal effects:
  • Belching
  • Vomiting
  • Abdominal pain

• Nephrotoxic (kidney-damaging) effects (in patients with previous kidney disorders):
  • Kidney disease (progressing to chronic kidney disease in severe cases)
  • Acute kidney injury
  • Inflammation
  • Tubular fibrosis
  • Interstitial nephritis

• Neurotoxic effects:
  • Hiccups
  • Coughing
  • Confusion
  • Seizures
  • Insomnia^2,10

The side effects of star fruit are attributed to the toxins, oxalic acid and caramboxin. The former causes GI disturbances and kidney damage, while the latter causes neurotoxicity (nervous system damage).²

As a member of the Oxalidaceae (wood sorrel) family, star fruits are rich in oxalic acid. The oxalic acid content is higher in homemade star fruit juice than in commercial star fruit juice and whole fresh fruit.^2,10

When fresh star fruit or star fruit juice is consumed in excess, oxalic acid, which usually binds with magnesium and calcium in the gut, is freely available for absorption. Thus, it enters the kidneys and causes damage. These side effects worsen on an empty stomach and when dehydrated.^4,10

Caramboxin affects the central nervous system (CNS), causing neurotoxic effects. Only people without kidney disorders are unharmed by it since it is excreted from the body.^2,10

Due to these side effects, the following people should avoid consuming star fruit:

• Elderly people, especially on an empty stomach or when dehydrated
• Diabetic patients (could result in oxalate nephropathy)
• Patients with kidney problems or those undergoing dialysis
• Patients with uraemia (could result in death)^2,10

There’s no toxic dose established for star fruit consumption, nor is there any specific treatment for its side effects. Hence, star fruits should be consumed in moderation and avoided by the people mentioned above.¹⁰

Summary

Star fruits are nutrient-dense tropical fruits with plenty of health benefits. They help with weight loss, promote liver and heart health, reduce cholesterol, and prevent and treat chronic diseases like CVD, diabetes, hypertension, and cancer. They also have anti-inflammatory properties and a high antioxidant capacity, since they’re a good source of vitamin C. 

Star fruits can easily be included in your diet as they pair well with other ingredients in many recipes. However, they should be eaten in moderation and avoided in some cases, as they have serious side effects when consumed in excess.