Grapefruit diet

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Grapefruit diet








Research and general acceptance



There are several diets or approaches to dieting that have been referred to as the “grapefruit diet.” The first two are fad diets that have been circulating via chain letters, photocopies, faxes, and e-mail since the 1930s. The third form might be better described as the regular use of grapefruit or grapefruit juice as part of a general approach to weight reduction. It received considerable attention following the 2004 publication of a study conducted at the Scripps Clinic in California.


According to the American Dietetic Association, the fad type of grapefruit diet began in the 1930s, when it was also known as the Hollywood diet. There were two regimens, a 7-day and a 21-day version, both of which were very low-calorie diets or VLCDs. The dieter consumed little except black coffee and half a grapefruit at each meal, with small amounts of salad and lean meat. This Depression-era version of the “Hollywood diet” was quite different from the Hollywood diet offered online as of 2007, which amounts to a 24- or 48-hour juice fast intended to detoxify the dieter’s body as well as promote rapid weight loss.

In the 1940s, the VLCD grapefruit diet reappeared under the name of the Mayo Clinic Diet—a name that has also been attached to several other so-called mono diets, one based on eggs and the other on meat. The Mayo Clinic has issued a disclaimer regarding the use of its name in connection with the grapefruit diet as well as other fad diets that have used the clinic’s name. It is also possible that the VLCD form of the grapefruit diet may have influenced Herman Tar-nower’s first version of the Scarsdale diet in the 1960s. The original mimeographed diet sheet that the doctor gave his overweight cardiology patients specified 18 servings of grapefruit—14 at breakfast and 4 for dessert in the evenings—over the two-week period of the diet, and some of his patients referred to the Scarsdale diet informally as a grapefruit diet.

The VLCD grapefruit diet has also been recommended since the 1970s as a detoxification diet. Some writers recommend taking apple cider vinegar along with the grapefruit in order to “flush the system of impurities.” The fact that the fiber in grapefruit speeds up the passage of foods through the intestine and eases constipation is another reason why some advocates of detoxification diets design their regimens around grapefruit.

The high-protein version of the grapefruit diet began to circulate at some point during the 1970s and has reappeared at various intervals since then. It is the variation most commonly found on Internet sites that post fad diets. Some forms of this diet claim that it works because grapefruit supposedly contains special “fat-burning” enzymes.

The term grapefruit diet has also been used by journalists since 2004 to refer to the findings of a 12-week research study conducted at the Scripps Clinic in California in 2003. The term diet is a bit of a misnomer, because the study was designed to measure the effectiveness of grapefruit and grapefruit products in treating insulin resistance as well as lowering weight in 91 overweight subjects who were not otherwise trying to diet. The study received considerable publicity and revived interest in incorporating grapefruit into nutritionally sound weight reduction diets. Its use of grapefruit in capsule form as well as fresh grapefruit, however, also prompted the development of several new lines of over-the-counter “miracle diet aids.”.


Very low-calorie grapefruit diet plan

The basic menu plan is the same for each day of the week:

  • Breakfast: 1/2 grapefruit + 2 slices of bacon + 2 boiled eggs + black coffee (no sugar) or unsweetened tea.
  • Lunch: 1/2 grapefruit + 1 cup of salad with low-calorie dressing + 8 ounces of lean chicken or water-packed tuna fish + black coffee (no sugar) or unsweetened tea.
  • Dinner: 1/2 grapefruit + as much salad with low-calorie dressing as desired + 8 ounces of lean chicken, lean beef, or fish + black coffee (no sugar) or unsweetened tea.
  • No snacks are allowed, and the only seasonings permitted for the meat or fish are herbs; no soy sauce, mustard, catsup, or other condiments are allowed.

The dieter is supposed to follow this diet for 12 days, then take two days off, and repeat the two-week cycle indefinitely.

High-protein grapefruit diet plan

This version of the grapefruit diet has been described as “just plain weird” because it comes with a curious set of rules as well as lists of foods that the dieter may or may not have. It also promises a weight loss of 52 pounds over 2-1/2 months.

“The Rules”:

  • You must drink eight 8-ounce glasses of water every day (64 ounces total).
  • At any meal you may eat until you are full.
  • You must eat the minimum of each food listed at each meal.
  • You cannot eliminate any item from the diet, especially the bacon at breakfast and the salads. You MUST eat the bacon and the salads. These combinations of food burn the fat; omitting one part of the combination will cause the whole thing not to work.


Cytochromes— Complex proteins within cell membranes that carry out electron transport. Grapefruit juice interferes with the functioning of an enzyme belonging to the cytochrome P-450 group.

Glycemic index (GI)— A system devised at the University of Toronto in 1981 that ranks carbohydrates in individual foods on a gram-for-gram basis in regard to their effect on blood glucose levels in the first two hours after a meal. There are two commonly used GIs, one based on pure glucose as the reference standard and the other based on white bread.

Insulin resistance A condition in which normal amounts of insulin in a person’s blood are not adequate to produce an insulin response from fat, muscle, and liver cells. Insulin resistance is often a precursor of type 2 (adult-onset) diabetes.

Lycopene— A plant pigment that appears red in natural light and is responsible for the red color of tomatoes. Grapefruit is rich in lycopene, which is a powerful antioxidant and is thought to retard skin aging and may help to protect against chronic diseases such as heart disease and cancer.

Metabolic syndrome— A group of risk factors related to insulin resistance and associated with an increased risk of heart disease. Patients with any three of the following five factors are defined as having metabolic syndrome: waist circumference over 102 cm (41 in) for men and 88 cm (34.6 in) for women; high triglyceride levels in the blood; low levels of HDL cholesterol; high blood pressure or the use of blood pressure medications; and impaired levels of fasting blood glucose (higher than 110 mg/dL).

Mono diet— A type of detoxification diet based on the use of only one food or beverage. Some versions of the grapefruit diet are essentially mono diets.

Pectin— A water-soluble heterosaccharide (complex molecule composed of a sugar molecule and a non-sugar component) found in the cell walls of higher plants. It is used primarily as a gelling agent in making jams and jellies, but can also be taken by mouth as a form of plant fiber to relieve constipation.

Placebo— An inert or medically inactive substance, often formulated to look like a pill or capsule, administered to subjects as part of clinical research trials to determine the effectiveness of a drug or treatment. Placebo comes from the Latin and means “I shall please,” because the name was first given to sugar pills dispensed by some doctors to satisfy some patients’ demands for drugs they didn’t need.

Pomelo— A large pear-shaped citrus fruit with a thick rind that was crossed with the sweet orange in the West Indies to produce the modern grapefruit.

Very low-calorie diet (VLCD)— A term used by nutritionists to classify weight-reduction diets that allow around 800 or fewer calories a day. Some versions of the grapefruit diet are VLCDs.

  • The grapefruit or fruit juice is important because it acts as a catalyst that starts the burning process. Don’t add to or reduce the amount of grapefruit or juice.
  • Cut down on coffee because it affects the insulin balance that hinders the burning process. Try to limit yourself to 1 cup of coffee at meal time.
  • Don’t eat between meals. If you eat the suggested foods, you will not get hungry.
  • You can fry food in butter and use generous amounts of butter on the vegetables.
  • Do not eat desserts, bread, or white vegetables or sweet potatoes.
  • You may have double or triple helpings of meat, salad, or vegetables.
  • Eat until you are stuffed. The more you eat, the more weight you will lose.
  • Stay on the diet 12 days, then stop the diet for 2 days and repeat.

The daily diet plan:

  • Breakfast: Either 1/2 grapefruit or 8 ounces of unsweetened fruit juice (any fruit) + 2 eggs any style + 2 slices of bacon.
  • Lunch: Either 1/2 grapefruit or 8 ounces of unsweetened fruit juice (any fruit) + salad with any dressing + meat any style and any amount.
  • Dinner: Either 1/2 grapefruit or 8 ounces of unsweetened fruit juice (any fruit) + salad with any dressing or a red or green vegetable cooked in butter or spices + meat or fish any style cooked any way + coffee or tea (1 cup).
  • Bedtime snack: 8 ounces of tomato juice or skim milk.

Foods the dieter may eat: red onions, bell peppers, broccoli, radishes, cucumbers, carrots, green onions, leaf spinach, cabbage, tomatoes, green beans, lettuce, chili (no beans), mayonnaise, any cheese, hot dogs, cole slaw, salad dressing, dried nuts, dill pickles.

Foods the dieter may not eat: white onions, potatoes, celery, peas, cereal, corn, starchy vegetables, potato chips, peanut butter, pasta, corn chips, jelly or jam, sweet pickles, pretzels, fruit, low-fat or diet salad dressings

2004 grapefruit research diet

The 91 subjects in this 12-week study were randomly assigned to four groups: one group received a placebo capsule plus 7 ounces of apple juice before each meal, the second group received grapefruit capsules plus 7 ounces of apple juice, the third group received 8 ounces of grapefruit juice plus a placebo capsule, and the fourth group received 1/2 of a fresh grapefruit plus a placebo capsule. At the end of the 12 weeks, the subjects in the three groups that had received some form of grapefruit had lost significantly greater amounts of weight than those in the group that had received only the placebo, with those who received the fresh grapefruit losing the most weight. The patients were not asked to make any other changes in their food intake, but they were required to take 30-minute walks three times a week.

Grapefruit diet capsules

As of 2007 there are two types of grapefruit pills or capsules sold over the Internet, both claiming to help people lose weight. The “grapefruit pectin diet tablets” are said to “help release fat deposits“that the dieter already carries on the stomach and hips. “They can also prevent new fat from penetrating the cells by redirecting it to the muscles where it is burned off, thereby eliminating fat deposits.” The pills contain 200 mg of grapefruit pectin, plus cellulose and fiber. Given the high fiber content of these pills, it is most likely that they simply speed up the dieter’s digestion and elimination.

The Grapefruit Solution Natural Diet, based on a book published in 2004, makes use of capsules that contain “pure, organic whole grapefruit. .. . Five years of study and research has gone into developing and perfecting the technique of taking whole grapefruit and converting it into concentrated power while retaining all the benefits of the entire grapefruit.” In addition to the capsules, however, this diet does emphasize the importance of exercise as well as a balanced diet of complex carbohydrates and protein foods.


The fad versions of the grapefruit diet are intended for rapid weight loss. They are usually recommended as a good way to lose weight after holiday-related overeating or to fit into a special outfit for an important occasion. Several of the versions available on the Internet, however, claim that the grapefruit diet can be used for weight maintenance or for long-term nutrition on a twelve-days-on, two-days-off schedule.

The 2004 research version of the diet is intended to assess the effectiveness of grapefruit in counteracting metabolic syndrome (a group of risk factors for heart disease related to insulin resistance) as well as its usefulness in weight reduction diets. Preliminary results indicate that regular inclusion of grapefruit in the diet is effective in helping patients lose weight at a moderate rate and in improving their response to insulin.


The fad versions of the grapefruit diet should be avoided in spite of their promises of rapid weight loss. The VLCD version does not allow enough calories to supply the daily energy needs of even a moderately active adult and is nutritionally unbalanced. The high-protein version is highly unlikely to help anyone lose weight, since its allowance of “meat any style and any amount” and “double or triple helpings” of meat and vegetables could easily encourage overeating.

Using grapefruit as an adjunct to a balanced weight-reduction diet by eating half a grapefruit before meals, however, appears to be helpful in reducing hunger cravings. It also contributes fiber and vitamins to the dieter’s daily intake.


General precautions

A general precaution for anyone seeking to lose weight is to consult a physician before trying any specific diet. This precaution is particularly important for adolescents, women who are pregnant or nursing, people with kidney or liver disorders, people with eating disorders, anyone who has had recent surgery, and anyone who needs to lose more than 30 pounds.

Drug interactions

Grapefruit contains certain compounds that interact with various types of medications in the digestive tract (it does not, however, affect drugs taken by injection). Although apple juice and orange juice may also interact with some prescription drugs, grapefruit containsthreecompoundsknownasnaringin,bergamottin, 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 subjects 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 consequences, 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 specific 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 compounds associated with Ayurveda or traditional Chinese 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.


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.


  • 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?

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 encountered by Europeans in the 1750s on the island of Barbados 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 hybridization occurred spontaneously in the citrus groves on the island or was carried out by native fruit growers.

The grapefruit was originally called the shattuck or shaddock until 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 Southwest. 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 diameter) weighs 128 grams, 116 of which are water. It contains 41 calories, 10.3 grams of carbohydrates (1.4 grams of fiber and 8.93 grams of fruit sugars), 0.81 grams of protein, and less than 0.13 grams of total fat. Grapefruit are rich in vitamin C (44 mg), vitamin A (1187 IU), lycopene (1453 mcgin red and pink varieties), and potassium (178 mg). Apart from concern about drug interactions, nutritionists consider grapefruit a healthful fruit to include in a well-balanced diet. Its high vitamin C content helps to protect against scurvy, while the lycopene contained in red and pink varieties is an antioxidant thought to slow down the aging of skin and connective tissue. Lycopene may also be important in preventing chronic diseases such as heart disease and prostatecancer. In addition, the fiber content of grapefruit is helpful in preventing constipation.

Evaluations of grapefruit in weight reduction diets

Grapefruit is considered a good food choice for people watching their weight because it is relatively filling thanks to its fiber content. It also has a low glycemic index (GI), which is a measurement of the rate at which carbohydrates in the food affect a person’s blood glucose level within two hours after eating the food. Foods with low GI scores break down slowly in the digestive tract and thus prevent sudden changes in the blood sugar level—an important consideration for persons with metabolic syndrome or type 2 diabetes and possibly for those watching their weight for other reasons. Grapefruit has a GI of 25 (pure sugar is 100), which is lower than the GI scores of apples (40), oranges (51), and bananas(51).

According to the research team at Scripps Clinic, it is not yet known as of 2007 why grapefruit appears to improve insulin response in overweight people or why it assists weight loss. Ongoing research may help to answer this question, but one finding at least is clear: grapefruit does not contain any miracle fat-burning enzymes.



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Rebecca J. Frey, PhD.