A large bitter-tart citrus, a hybrid of pomelo and sweet orange that emerged in 18th-century Barbados, eaten fresh or juiced and famous for drug interactions.
A young fruit
Grapefruit is one of the youngest cultivated citruses — a chance hybrid of pomelo and sweet orange that arose in Barbados around 1750. The name “grapefruit” appeared in 1814, referring to the fact that the fruit grows in clusters resembling oversized grapes. Commercial cultivation didn’t begin until 1823 in Florida.
By comparison, oranges, lemons, and limes have been cultivated for thousands of years.
A drug-interaction warning
Grapefruit is unusually pharmacologically active. Compounds called furanocoumarins (especially bergamottin and 6’,7’-dihydroxybergamottin) inhibit a key liver enzyme — cytochrome P450 3A4 — that metabolizes many medications. With grapefruit’s furanocoumarins blocking the enzyme, drug levels in the blood can rise dangerously.
The effect was discovered accidentally in 1989 during a hypertension drug study. Today, dozens of drugs carry grapefruit warnings, including:
- Statins (atorvastatin, simvastatin)
- Some calcium channel blockers (felodipine)
- Some psychiatric medications (buspirone)
- Some immunosuppressants (cyclosporine)
- Some erectile dysfunction medications (sildenafil)
A single 8-oz glass of grapefruit juice can affect drug metabolism for over 24 hours. The effect is enzyme-inhibition rather than direct chemical interaction; you can’t avoid it by spacing out grapefruit and pills.
A bitter compound
Grapefruit’s distinctive bitterness comes from naringin, a flavonoid concentrated in the white pith and outer layers of the segments. Pink and red grapefruit varieties have less naringin and more sweetness; white grapefruit is the most bitter. Modern hybrids like Oroblanco and Sweetie are deliberately bred for very low bitterness.
Pomelo, the parent
Pomelo (Citrus maxima) is the larger, less bitter ancestor of grapefruit. It’s a popular fresh-eating fruit in Southeast Asia and Mexico — the segments separate cleanly, the membranes are thicker and easily peeled away, and the flavor is sweet-tart without the medicinal bitterness of grapefruit.
Pomelos can grow to 30 cm in diameter and weigh several kilograms. The most common varieties in the U.S. are Chandler and Reinking.
A diet myth
The “grapefruit diet” — built on the idea that grapefruit contains fat-burning enzymes — has been promoted in various forms since the 1930s. There’s no compelling evidence that grapefruit is uniquely effective for weight loss; modest effects in some studies (eating half a grapefruit before meals) probably reflect the fiber content and the appetite-suppressing effect of acidic, low-calorie food before meals. Any low-calorie filling food would likely produce similar results.