Grapefruit juice is the sour juice of, well, grapefruits. In fact, pure grapefruit juice is very, very sour. Sometimes bitter. But once you acquire (or get past) its taste, you will find that it's a unique, refreshing beverage with lots of uses in promoting one's health.
Nutritional Information
Grapefruit juice, like other citrus juices, is chock-full of Vitamin C and potassium. But that's not all. A cup of fresh, pink grapefruit juice contains:
Fresh white grapefruit juice has less Vitamin A due to it having less beta-carotene; white juice has only 81 IUs of the vitamin. Canned unsweetened juice has fewer vitamins all the way around, and sweetened juice cocktails can have quite a lot more calories and quite a lot fewer nutrients, so 100% unsweetened juice is best if you're interested in its healthy attributes.
Cancer Protection
While not as powerful in this area as oranges and tangerines, grapefruit juice contains a variety of flavonoids and glucosides called limonoids that are thought to protect against cancer. Lab tests with rodents showed protection against lung, mouth, breast, prostate, and colon cancers.
Weight Loss
Anyone who was alive during the 70s remembers the fad grapefruit diet; as it turns out, it was not as goofy an idea as we might have thought.
Researchers at Dr. Ken Fujioka's laboratory at the Scripps Clinic in San Diego recently did a study on 100 obese patients. Participants who ate half a grapefruit at each meal lost an average of nearly 4 pounds during the 12-week study; those who drank a glass of grapefruit juice lost on average 3.3 pounds. Some people in the study lost a good deal more weight.
An as-yet-unidentified compound in grapefruit juice appears to reduce and regulate insulin levels in the blood; reduced insulin levels in turn affect hunger and blood sugar levels and improve the body's metabolism. The compound may prove useful for diabetics as well.
Grapefruit Juice and Yeast Infections
Many women are plagued by maddening, uncomfortable yeast infections. For some, drinking a glass of grapefruit juice every day staves off the infections, either by acidifying the woman's system or due to an unknown botanical compound that helps the body fight off fungal infection.
Grapefruit juice is cheaper and less toxic than the antifungal drugs used to treat yeast infections. However, women who want to give the juice a try should watch out for drug interactions and should also avoid sweetened juices and juice cocktails. Sweetened juices are loaded with sugar, and a high-sugar diet is commonly believed to make a person more vulnerable to a yeast infection.
The Dark Side of The Glass of Sunshine
If you drink a lot of grapefruit juice, the acid may cause indigestion or (if you're susceptible to them) canker sores. However, treatment for these side effects are pretty simple: don't drink so much juice. Alternately, try taking a calcium carbonate antacid along with your juice.
A more problematic feature of grapefruit juice is that it causes you to absorb more of certain types of drugs, thus potentially causing accidental overdose. It does this by inhibiting naturally-occuring enzymes in the intestines (specifically, cytochrome P450 isoenzymes) that break down a certain portion of said drugs before they have a chance to enter the person's bloodstream.
If a person knows what he/she is doing, of course, this means that grapefruit juice can potentially allow you to take much less of a medication and get the same beneficial effect from it, thus conserving the medication and saving money on prescriptions. But unless one is working closely with a pharmacist, its best not to try that at home.
The amount of grapefruit juice needed to produce the drug-enhancing effect varies; some studies show that as little as a single glass of juice can do it. Others didn't show an effect unless subjects downed nearly a quart of the juice. However, a 2-hour gap between taking a medication and drinking the juice seems sufficient to avoid interactions.
Several compounds in grapefruit juice have been identified as causing the effect, mainly quercetin, kaempferol, and furanocoumarin compounds such as naringin. There may very well be others.
Drugs that should not be taken with grapefruit juice include:
All the above are prescription medications; there's been no evidence so far that grapefruit juice interacts badly with any over-the-counter medications. In many instances, the precise effects haven't been worked out, but all the above medications have the potential for some kind of interaction. The drugs that you should absolutely avoid taking with grapefruit juice are the calcium channel blockers (which can dangerously lower blood pressure), drugs that can depress the central nervous system such as busipirone and benzodiazepines (an overdose of such drugs can cause accidents or put you in a coma), or drugs used to regulate heart rhythm like amiodarone.
Juicier Juice
However, there's one central nervous system depressant that grapefruit juice goes just dandy with: alcohol! If you're not a teetotaler, try the following potent potables:
Sources:
http://scrippshealth.org/scrippsnews_1714.asp
http://www.nal.usda.gov/
http://www.pharmacists.ca/content/hcp/resource_centre/drug_therapeutic_info/
http://www.cancerpage.com/cancernews/cancernews640.htm
http://www.torsades.org/consumers/06-grapefruit-juice.htm | 
