One medium orange has about 70 milligrams (mg) of vitamin C, nearly enough to meet your basic daily needs. But ounce for ounce, lemons actually contain the most (77 mg in 3.5 ounces), followed by oranges (53 mg), pink grapefruit (37 mg), white grapefruit (33 mg), limes (29 mg) and tangerines (27 mg). The exact amount depends on where the fruit was grown, how it was handled and where on the tree the fruit was located.
Citrus fruits are a good source of folate and potassium, with small amounts of magnesium, calcium and more. They are often rich in fiber—notably pectin, which helps lower cholesterol. They also contain dozens of phytochemicals, including carotenoids and limonoids. Citrus flavonoids such as hesperetin (in oranges), naringin (in grapefruit) and tangeritin (in tangerines) have been shown in lab studies to have cholesterol-lowering, antioxidant, anti-inflammatory and anti-cancer properties. Red/pink grapefruit is a great source of lycopene.
A cup of citrus juice has more vitamin C than a piece of whole fruit because it is concentrated (it takes nearly a pound of oranges to make a cup of juice). But it is also higher in sugar and calories—and lacks the fiber of the whole fruit. A glass of orange or grapefruit juice is a good way to start the day (especially if it’s fortified with calcium), but it is better to eat whole fruit, which has less effect on blood sugar and is more filling. Fresh OJ is slightly higher in C and other nutrients than juice made from concentrate.
Many of the substances in the pulp are also in the peel, though you’re not likely to eat much of it. The peel consists of two parts: the inner spongy white albedo, which is the primary source of pectin, and the outer flavedo (or “zest”), where carotenoid pigments and fragrant volatile oils are found. Some nutrients in the pulp, such as vitamin C and folate, are also found in the peel.
Oranges grow in warm climates but need cool nights to turn orange. If nights are warm, oranges can remain slightly green. Another factor is “re-greening,” when fully developed oranges absorb some of the chlorophyll produced by the tree and turn partly green again. These oranges are extra-ripe and often sweeter. To make oranges uniformly orange, producers often expose them to ethylene (a harmless gas that some fruits naturally release) or treat them with vegetable dye. Whatever the color, oranges are always picked when mature and do not ripen further off the tree.
Grapefruit and its juice can boost blood levels of certain medications to potentially dangerous levels. Substances in the fruit inhibit an enzyme that helps break down the drugs. The interaction happens fast and can last 24 hours or longer. But it’s highly unpredictable. If you take medication, check with your doctor or pharmacist. Common drugs: Cholesterol-lowering statins, certain calcium channel blockers (for high blood pressure), tranquilizers, antihistamines and HIV drugs. Seville oranges, pomelos and tangelos may have a similar effect.
It’s a myth that grapefruit contains a special enzyme that digests and burns fat and promotes weight loss. While there are no such fat-burning substances, grapefruit is low in calories (40 in half a medium fruit) and filling, which is why it may help some people lose weight.