Momordica charantia, known as bitter melon, bitter gourd, bitter squash or balsam-pearin English, has many other local names. Goya from Okinawan and karela from Sanskrit are also used by English-language speakers.
It is a tropical and subtropical vine of the family Cucurbitaceae, widely grown in Asia, Africa, and the Caribbean for its edible fruit, which is extremely bitter. Its many varieties differ substantially in the shape and bitterness of the fruit. As the name implies, this vegetable is a melon that is bitter. There are two varieties of this vegetable: One grows to about 20 cm long, is oblong and pale green in color. The other is the smaller variety, less than 10 cm long, oval and has a darker green color.
Both varieties have seeds that are white when unripe and that turn red when they are ripe. The vegetable-fruit turn reddish-orange when ripe and becomes even more bitter.
Bitter gourds are very low in calories but dense with precious nutrients. It is an excellent source of vitamins B1, B2, and B3, C, magnesium, folate, zinc, phosphorus, manganese, and has high dietary fiber. It is rich in iron, contains twice the beta-carotene of broccoli, twice the calcium of spinach, and twice the potassium of a banana.
Bitter melon contains a unique phyto-constituent that has been confirmed to have a hypoglycemic effect called charantin. There is also another insulin-like compound known as polypeptide P which have been suggested as insulin replacement in some diabetic patients. [source: http://juicing-for-health.com/health-benefits-of-bitter-gourd.html]
In addition to being a food ingredient, bitter melon has also long been used as a herbal remedy for a range of ailments, including type 2 diabetes.
The fruit contains at least three active substances with anti-diabetic properties, including charantin, which has been confirmed to have a blood glucose-lowering effect, vicine and an insulin-like compound known as polypeptide-p.
These substances either work individually or together to help reduce blood sugar levels.
It is also known that bitter melon contains a lectin that reduces blood glucose concentrations by acting on peripheral tissues and suppressing appetite – similar to the effects of insulin in the brain.
This lectin is thought to be a major factor behind the hypoglycemic effect that develops after eating bitter melon.