The grapefruit (Citrus × paradisi), is a subtropical citrus tree known for its bitter fruit, an 18th-century hybrid first bred in Barbados. When found, it was named the “forbidden fruit”; it has also been misidentified with the pomelo or shaddock (C. maxima), one of the parents of this hybrid, the other being sweet orange (C. × sinensis).
These evergreen trees usually grow to around 5–6 meters (16–20 ft) tall, although they can reach 13–15 meters (43–49 ft). The leaves are dark green, long (up to 150 mm, 6 inches) and thin. It produces 5 cm (2 in) white four-petaled flowers. The fruit is yellow-orange skinned and largely an oblate spheroid; it 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 become popular since the late 19th century; before that it was only grown as an ornamental plant. The United States quickly became a major producer of the fruit, with groves in Florida, Texas, Arizona, and California. In Spanish, the fruit is known as toronja or pomelo.
Nutritional properties
Grapefruit is an excellent source of many nutrients and phytochemicals that contribute to a healthy diet. Grapefruit is a good source of vitamin C, contains the fiber pectin, 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 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 (GSE) has been claimed to have strong antimicrobial properties against bacteria and fungi. However, no studies have demonstrated any efficacy by GSE as an antimicrobial for either bacteria or fungi. Additionally, although GSE is promoted as a highly effective plant-based preservative by some natural personal care manufacturers, studies have shown that the apparent antimicrobial activity associated with GSE preparations is merely due to contamination with synthetic preservatives.
Since grapefruit juice is known to inhibit enzymes necessary for the clearance of some drugs and hormones, some have hypothesized that grapefruit juice may play an indirect role in the development of hormone-dependent cancers. 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. However, a 2008 study has shown that grapefruit consumption does not increase breast cancer risk and found a significant decrease in breast cancer risk with greater intake of grapefruit in women who never used hormone therapy.
Grapefruit contains large quantities of a simple polyamine called spermidine, which may be related to aging. It is known to be necessary for cell growth and maturation, and as cells age their level of spermidine is known to fall. Scientists have shown that feeding spermidine to worms, fruit flies and yeast significantly prolongs their lifespan. In addition, adding spermidine to the diet of mice decreased molecular markers of aging, and when human immune cells were cultured in a medium containing spermidine, they also lived longer.