Grapefruit
The grapefruit is a subtropical citrus tree grown for its fruit which was originally named the "forbidden fruit" of Barbados.
These evergreen trees are usually found at around 5-6 m tall, although they can reach 13-15 m. The leaves are dark green, long (up to 150 mm) and thin. It produces 5 cm white four-petalled flowers. The fruit is yellow-skinned, largely oblate and ranges in diameter from 10-15 cm .  The flesh is segmented and acidic, varying in color depending on the cultivars, which include white, pink and red pulps of varying sweetness.  The 1929 US Ruby Red (of the Redblush variety) has the first grapefruit patent.
The fruit has only become popular from the late 19th century; before that it was only grown as an ornamental plant. The US quickly became a major producer of the fruit, with orchards in Florida, Texas, Arizona, and California. In Spanish, the fruit is known as toronja or pomelo.

# History
The fruit was first documented in 1750 by the Rev. Griffith Hughes describing specimens from Barbados. Currently, the grapefruit is said to be one of the "Seven Wonders of Barbados." It had developed as a hybrid of the pomelo (Citrus maxima) with the sweet orange (Citrus sinensis), though it is closer to the former. It was brought to Florida by Odette Philippe in 1823. Further crosses have produced the tangelo (1905), the minneola (1931), and the sweetie (1984). The sweetie has very small genetic and other differences from pomelo.
The grapefruit was known as the shaddock or shattuck until the 1800s. Its current name alludes to clusters of the fruit on the tree, which often appear similar to grapes. Botanically, it was not distinguished from the pomelo until the 1830s, when it was given the name Citrus paradisi. Its true origins were not determined until the 1940s. This led to the official name being altered to Citrus  paradisi. Grapefruit peel oil is used in aromatherapy and it is historically known for its aromatic scent.
The 1929 Ruby Red patent was associated with real commercial success, which came after the discovery of a red grapefruit growing on a pink variety. Only with Ruby Red the grapefruit transformed into a real agricultural fruit. The Red grapefruit, starting from the Ruby Red, has even become a symbol fruit of Texas, where white "inferior" grapefruit were eliminated and only red grapefruit were grown for decades. Using radiation to trigger mutations, new varieties were developed to retain the red tones which typically faded to pink, with Rio Red is the current (2007) Texas grapefruit with registered trademarks Rio Star and Ruby-Sweet, also sometimes promoted as "Reddest" and "Texas Choice".

# Production
The United States of America is the top producer of grapefruit and pomelo followed by China and Mexico.

# Colors and flavors
Grapefruit comes in many varieties, determinable by color, which is caused by the pigmentation of the fruit in respect of both its state of ripeness and genetic bent.  The most popular varieties cultivated today are red, white, and pink hues, referring to the inside, pulp color of the fruit. The family of flavors range from highly acidic and somewhat bitter to sweet and tart.  Grapefruit mercaptan, a sulfur-containing terpene, is one of the substances which has a strong influence on the taste and odor of grapefruit, compared with other citrus fruits.

# Drug interactions
Grapefruit can have a number of interactions with drugs, often increasing the effective potency of compounds.  Grapefruit contains naringin, bergamottin and dihydroxybergamottin, which inhibit the protein isoform CYP3A4 in the intestine. It is via inhibition of this enzyme that grapefruit increases the effects of a variety of drugs. The effect of grapefruit juice with regard to drug absorption was originally discovered in 1989. However, the effect became well-publicized after being responsible for a number of deaths due to overdosing on medication.

# Nutritional properties
Grapefruit is an excellent source of many nutrients and phytochemicals, able to contribute to a healthy diet. Grapefruit is a good source of vitamin C, pectin fiber, and the pink and red hues contain the beneficial antioxidant lycopene. Studies have shown grapefruit helps lower cholesterol and there is evidence that the seeds have high levels of antioxidant properties. Grapefruit forms a core part of the "grapefruit diet", the theory being that the fruit's low glycemic index is able to help the body's metabolism burn fat.
Grapefruit seed extract has been claimed to be a strong antimicrobial with proven activity against bacteria and fungi. However, studies have shown the efficacy of grapefruit seed extract as an antimicrobial is not demonstrated.  Although GSE is promoted as a highly effective plant-based preservative by some natural personal care manufacturers, studies indicate the universal antimicrobial activity associated with GSE preparations is merely due to contamination with synthetic preservatives.
A 2007 study found a correlation between eating a quarter of grapefruit daily and a 30% increase in risk for breast cancer in post-menopausal women.  The study points to the inhibition of CYP3A4 enzyme by grapefruit, which metabolizes estrogen.