Excerpts from a 4/28/10 article in the Nigerian Guardian News
Star fruit has been shown to be rich in antioxidants and vitamin C and low in sugar, sodium and acid. It is also a potent source of both primary and secondary polyphenolic antioxidants. Antioxidants are compounds that reverse the damage caused by free radicals or reactive oxygen species.
According to a study, “Pharmacognistic Evaluation and Physiochemical Analysis of Averrhoa carambola Fruit” published recently in the Journal of Herbal Medicine and Toxicology, the ripe star fruit is considered as digestible, tonic strengthening, for bleeding piles and causing biliousness. The dried fruit is also used in fever; it is cooling and possesses antiscorbutic properties. It is considered as one of the best Indian cooling medicines.
The researchers wrote: “Preliminary phytochemical analysis indicated presence of saponins, tannins, alkaloids and flavonoids. In last four decades the scientists are keen to evaluate many plant drugs used in medicinal folklore. It is due to their specific healing properties, healthy action and non-toxic effects.
“In this dimension pharmacognostic studies on Averrhoa carambola L. fruit is a substantial step and it further requires a long-term study to evaluate pharmacological action as well as therapeutic efficacy and toxicity of fruit to establish as the drug. The pharmacognostic study of the Averrhoa carambola L. fruit has been carried out for the first time. This could also serve in the identification and preparation of a monograph on the plant.”
In India, the ripe fruit or its juice may be taken to counteract fever. A salve made of the fruit is employed to relieve eye afflictions. In Brazil, the star fruit is recommended as diuretic in kidney and bladder complaints.
In Chinese Materia Medica it is used to quench thirst, increase the salivary secretion, and in fever. In Ayurveda, the ripe fruit is considered as digestive, tonic and causes biliousness.
The dried star fruit is also used in fever; it is cooling and possesses antiscorbutic properties. It is considered as one of the best Indian cooling medicines. Fruits and its fruit juice are used as antioxidant and astringent.
Star fruit has also been shown to reduce blood sugar levels and a possible treatment for diabetes.
Researchers at the Department of Food Science, National Chung Hsing University, Taiwan, Republic of China, investigated by some in vitro methods the hypoglycemic effects of several insoluble fiber-rich fractions (FRFs) including insoluble dietary fiber, alcohol-insoluble solid, and water-insoluble solid isolated from the pomace of Averrhoa carambola.
The study titled “”Insoluble fiber-rich fractions derived from Averrhoa carambola: hypoglycemic effects determined by in vitro methods” was published in the journal Lebensmittel-Wissenschaft und-Technologie.
The study evidenced that these three insoluble FRFs could effectively adsorb glucose, retard glucose diffusion, postpone the release of glucose from starch, and inhibit the activity of amylase to different extents. All of these mechanisms might create a concerted function in lowering the rate of glucose absorption and as a result decrease the postprandial serum glucose concentration.
The researchers wrote: “Our results revealed that the hypoglycemic effects of these insoluble FRFs were significantly stronger than that of cellulose. Therefore, it was suggested that they could be incorporated as low-calorie bulk ingredients in high-fiber foods to reduce calorie level and help control blood glucose concentration.”
Researchers have also analysed the potential topical anti-inflammatory activity of Averrhoa carambola in mice.
Preliminary results from the Brazilian researchers from the Universidade Estadual de Ponta Grossa, Ponta Grossa, PR, support the popular use of A. carambola as an anti-inflammatory agent and open up new possibilities for its use in skin disorders.
Inflammatory skin disorders, such as psoriasis and atopic dermatitis, are very common in the population; however, the treatments currently available are not well tolerated and are often ineffective.
The present study provides evidence that A. carambola leaves have a relevant topical anti-inflammatory effect in a model of cutaneous inflammation in mice. The study showed that the plant reduced edema and inhibited the cellular migration of polymorphonuclear leukocytes, an important step in the inflammatory process.
The researchers wrote: “Averrhoa carambola L. (Oxalidaceae) is an Asian tree that has been used in traditional folk medicine in the treatment of several skin disorders. The present study evaluates the topical anti-inflammatory effects of the crude ethanolic extract of A. carambola leaves, its hexane, ethyl acetate, and butanol fractions and two isolated flavonoids on skin inflammation. Anti-inflammatory activity was measured using a croton oil-induced ear edema model of inflammation in mice.
The researchers noted that the star fruit tree and is commonly used to treat headaches, vomiting, coughing and hangovers. They wrote: “Furthermore, it is used as an appetite stimulant, a diuretic, and as an anti-diarrheal and febrifugal agent. Star fruit has been used in the treatment of eczemas. In addition, the extract obtained through decocting the leaves of star fruit has been used in the treatment of diabetes.
“Phytochemistry studies have shown that the fruit of A. carambola is rich in antioxidants, especially polyphenolic compounds, which act against reactive oxygen species. Furthermore, the insoluble fibers of the star fruit slow the absorption of carbohydrates, significantly reducing blood glucose levels. The fiber can also act to prevent cardiovascular disease by reducing serum triglyceride and total cholesterol levels. Lastly, selective activity against brain tumor cells was observed with an alcoholic extract from the stems of star fruit, while an extract from the leaves was effective against liver carcinoma cells.”
However, researchers say a small per cent of the human population should be cautious of the fruit for health reasons. They say like the grapefruit, star fruit contains oxalic acid, which can be harmful to individuals suffering from kidney failure or under kidney dialysis treatment. Consumption by those with kidney failure can produce hiccups, vomiting, nausea, and mental confusion. Fatal outcomes have been documented in some patients.
Like the grapefruit, star fruit is considered to be a potent inhibitor of seven cytochrome P450 isoforms. These enzymes are significant in the first-pass elimination of many medicines, and thus, the consumption of star fruit or its juice in combination with certain medications can significantly increase their effective dosage within the body.