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US: “Health benefits and risks of grapefruit and grapefruit juice”

The grapefruit probably originated as a natural hybrid cross between the pomelo, which is the largest (up to a foot in diameter) of the citrus fruits, and a sour or bitter orange, or it may simply have developed as a mutant of the pomelo. In the early 19th century, grapefruits were grown in Jamaica, where perhaps the fruit got its name as they grew in clusters, “like grapes,” in certain trees.

Grapefruits did not become an important food source until much later, perhaps in the 1880s, when a seedless variety, the Marsh, was discovered growing in Florida. Other more popular varieties are the Thompson seedless pink fruit (1913) and the seedless Ruby red type (1929).

The grapefruit is a misnamed fruit because it looks nothing like a grape nor is it even a close family relative to the grape in the plant kingdom. The grapefruit is a member of the citrus family and probably originated in the Caribbean, perhaps in Barbados, around 1750. It was initially called a “small shaddock,” after a Captain Shaddock of the East India Company, who had imported the pummelo (also called the “pomelo”), or “large shaddock,” from Malaysia or Indonesia.

Today, most grapefruit is grown in the United States, primarily in Florida, but also in California, Arizona, and Texas. The growing season in Florida now extends from September through June. About two-thirds of the annual grapefruit crop is processed, mostly to juice or to frozen juice concentrate. Not all Americans drink grapefruit juice, but perhaps they should.

Nutritionally, grapefruits are low in calories (only about 40-60 calories per half a grapefruit) and are a good source of fiber, pectin, potassium, magnesium, vitamin C, thiamin, and niacin as well as a fair source of folic acid. Many of the grapefruit juice drinks are further fortified by adding additional vitamin C and other micronutrients, especially calcium. Grapefruits also contain bioflavonoids, which are vitamin-like substances that have certain anti-cancer properties and other functions.

One of the bioflavonoids is naringin, the principal component that gives the grapefruit its tart or bitter taste that makes some people “pucker” when they eat grapefruit or drink grapefruit juice. Sometimes naringin will precipitate out as aesthetically objectional crystals. The Japanese have developed an enzyme technology to breakdown naringin to products that will not form crystals.

Pectin is found in the pulp, as well as in the rind. It contains a soluble fiber that can bind to and lower cholesterol. For the most part it is not digested. In clinical studies, grapefruit pectin reduced circulating levels of “bad” LDL-cholesterol by about 12 percent. In experimental animal studies, grapefruit pectin reduced narrowing of blood vessels with atherosclerotic hardening of the arteries by 50 percent.

There is a misconception that grapefruit or grapefruit juice contains a “fat burner.” This has led to the recurring intermittent popularity of the “grapefruit diet,” sometimes also called the “Hollywood diet,” for weight reduction. There is no anti-obesity ingredient in grapefruits, but substituting grapefruit or unsweetened grapefruit juice for other dietary foods can dramatically reduce the number of calories consumed. It is this caloric reduction that causes weight loss, not the actual grapefruit.

The grapefruit continues to receive a lot of medical attention because it interacts with certain prescribed medications. Components of the grapefruit can influence the function of certain enzymes along the gastrointestinal tract or in the liver, and these interactions influence the rate at which certain medications can be broken down or removed from the body. Much of the past attention had focused on felodipine (marketed as Plendil), a popular medication for treating hypertension. When this occurs, the level of the blood pressure lowering medication in the body becomes too high, by as much as a five-fold increase. As a result, blood pressure may fall too low, causing symptoms of lightheadedness, dizziness, weakness or even fainting. It does not take much grapefruit or grapefruit juice to make this happen, especially if it is consumed on a regular basis. There is great individual variability, however, on who will and who will not be reactors.

Another group of medications that interact with the grapefruit are the “statins,” which are now widely prescribed to lower blood cholesterol levels. There are many other medications, however, that also interact with grapefruits. A partial list (using drug generic names) would include alprazolam, atorvastatin, benzodiazepines, buspirone, carvediol, cerivastatin, cisapride, clomipramine, coumadin, cyclosporine, ethinyl, estradiol, felodipine, lovastatin, nifedipine, nimodipine, saquinavir, simvastatin, tacrolimus, testosterone, triazolam.

Since the interactions of most drugs with various foods are generally not systematically studied before the drugs are released by the FDA for public use, this is probably only a partial list. Indeed, there are many other foods besides the grapefruit that have the potential for interacting with prescribed medications or over-the-counter drugs. In fact, these foods number probably in the hundreds, and include such items as broccoli, coffee, and many dairy products, especially yogurts, several cheeses and even milk.

So, what should you do? The “standard answer” might be to “ask your doctor,” but the potential for interactions is so great, as are the number of medications and the number of different foods, that it would be a very rare physician or pharmacist who would have all of the answers you might need. Besides, not all patients react in the same way and some do not react at all.

Your best chance of discovering a food-drug interaction is to be aware of the major side effects of any given medication you are taking. If you are having an unusual amount of adverse side effects, or if the medication is not quite working as well as it is supposed to do, you might at least consider a food-drug interaction.

It is better to be safe than sorry.


Publication date: 11/12/2009


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