Encyclopedia of Diets - A Guide to Health and Nutrition

and dihydroxybergamottin, which inhibit a family of

enzymes in the intestine known as the cytochrome

P450 system—in particular an enzyme called

CYP3A4. CYP3A4 metabolizes many drugs; when it

is inhibited by grapefruit juice, it increases the potency

of a medicine by allowing more of it to enter the

bloodstream. This effect of grapefruit juice was first

discovered in 1989 by a group of researchers in

Ontario who were studying the effects of alcohol on

a blood pressure drug called Plendil. The scientists

needed a liquid that would hide the taste of alcohol

from their test subjects, and used grapefruit juice to do

so. They were surprised to discover that the blood

levels of the blood pressure drug went up in the sub-

jects who received grapefruit juice alone as well as

those who received a mixture of grapefruit juice and

alcohol. Most interactions between grapefruit juice

and prescription drugs do not have serious consequen-

ces, but others are potentially fatal.

Here is a list of families of medications known to

interact with grapefruit juice. Readers should consult

their doctor or a pharmacist if they are taking a spe-

cific medication that belongs to any of these groups:

Calcium channel antagonists (given to treat high

blood pressure).

Immunosuppressants (given to control autoimmune

diseases).

Statins (given to reduce blood cholesterol levels).

HIV protease inhibitors (given to treat HIV infection).

Antihistamines (given to treat seasonal allergies).

Antiarrhythmics (given to control irregular heartbeat).

Sedatives, sleep medications, and benzodiazepine

tranquilizers.

Birth control pills.

Selective serotonin reuptake inhibitors (given to treat

depression).

Drugs given for male impotence.

Some anti-migraine drugs.

In addition, people who are using herbal teas,

other Western herbal preparations, or herbal com-

pounds associated with Ayurveda or traditional Chi-

nese medicine should consult their doctor or a

pharmacist before beginning a grapefruit diet, as the

chemicals in herbs can interact with grapefruit as well

as with prescription medications.

Risks

The risks of using the fad versions of the grapefruit

diet include nutritional imbalance (for both versions)

and weight gain (for the high-protein version). The

researcher who designed and conducted the Scripps

Clinic trial has specifically warned people against the

fad grapefruit diets, saying that both are unhealthy.

The risk of a severe interaction between grapefruit

and prescription drugs can be minimized by checking

with a physician or pharmacist before adding large

amounts of grapefruit or grapefruit juice to the diet.

Research and general acceptance

Basic nutritional information about grapefruit

Unlike some other fruits, such as apples, grapes,

and lemons, that have figured in mono diets, grapefruit

is a relatively new addition to the human table. It was

not known to the ancient world and was first encoun-

tered by Europeans in the 1750s on the island of Bar-

bados in the West Indies. Grapefruit (Citrus paradisi)

developed as a hybrid of the pomelo (Citrus maxima), a

large citrus fruit with a sour taste, and the sweet orange

(Citrus sinensis). It is not known whether the hybrid-

ization occurred spontaneously in the citrus groves on

the island or was carried out by native fruit growers.

The grapefruit was originally called theshattuck

orshaddockuntil the 1820s. The name came from a

Captain Shaddock, a 17th-century Englishman who

had brought the first pomelo seeds to Barbados in

1693. In 1823 the new hybrid was brought to Florida
      by a Frenchman named Odette Philippe; it was first
      cultivated only as an ornamental plant. By the 1880s,
      however, grapefruit were being shipped from Florida
      to New York and Philadelphia. It was not until the
      1940s that improved methods of packaging and faster
      transportation made grapefruit a household favorite
      in the Northeast as well as in Florida and the South-
      west. As of 2007, the United States produces 41% of
      the world’s grapefruit.
      According to the U.S. Department of Agriculture
      (USDA), half a standard grapefruit (4 inches in diam-
      eter) weighs 128 grams, 116 of which arewater.It
      contains 41 calories, 10.3 grams of carbohydrates
      (1.4 grams of fiber and 8.93 grams of fruit sugars),

QUESTIONS TO ASK YOUR

DOCTOR

 Are any of my prescription medications known

to interact with grapefruit?

 What is your opinion of the Scripps Clinic study?

 Are there any health risks that you know of

related to adding grapefruit to a well-balanced

weight reduction diet?

Grapefruit diet