Grapefruit is often touted as a health superfood and included in a number of “detox” protocols, and for many reasons, this is rightly so. However, for people on certain conventional/prescription drugs, grapefruits can pose a serious health risk.

Grapefruits are very high in Vitamin C, with one grapefruit containing more than 60-70% of your daily minimum vitamin C intake. In addition they contain good levels of Vitamin A, and small amounts of vitamin E, calcium, magnesium, potassium, thiamin, riboflavin, niacin, folate, pantothenic acid, phosphorus, zinc and copper.

Grapefruits also contain pectin and flavonoid antioxidants such as naringenin, naringin, lycopene (found primarily in pink grapefruits), beta-carotene, xanthin and lutein.

These micronutrients and enzymes can provide a number of health benefits including strengthening the immune system, boosting metabolism, reducing kidney stone risk, helping to normalise blood cholesterol levels, and fighting bacterial, viral and fungal infections.

Grapefruit (including grape seed oil and essential oil) is often used in cancer prevention protocols and in liver and gall bladder cleanses.

However, research shows that grapefruits (as well Seville (sour) oranges and tangelos) have chemical compounds which interfere with the body’s cytochrome P-450 detox pathway enzymes, thereby posing a health risk to people taking prescription/conventional drugs. Here is how:

The cytochrome P-450 is a family of enzymes found in all tissues of the body and in particularly high levels in liver cells. These enzymes are essential, among other things:

  • during phase I of liver detoxification (a metabolic process),
  • to convert extraneous sources of toxins, chemicals (including drugs), alcohols and carcinogens into harmless substances and eliminating the by-products
  • for the synthesis of Vitamin D and hormones (for instance by assisting the conversion of cholesterol into pregnenelone, the precursor to other hormones like estrogen, testosterone, cortisol and DHEA)

Research shows that the chemical compounds found in grapefruits called furanocoumarins are the ones that seem to interfere with cytochrome P-450 3A4 isoenzymes (3A4) in the liver and intestinal wall.

Furanocoumarins do not interact directly with conventional/prescription drugs. Instead, they bind to the 3A4 enzyme, reducing the absorption of certain drugs. In other words, they block the 3A4 enzyme, allowing the drugs to pass from your gut to your bloodstream much more easily. Blood levels of the drugs will therefore rise faster and higher than normal, in some cases reaching dangerously high levels.

This interaction can happen up to 72 hours after eating grapefruit or drinking grapefruit juice. Furthermore, the list of drugs that can be affected by these chemicals has risen sharply in recent years. As at the end of 2012, a Canadian study showed that more than 85 current drugs can interact with grapefruit, and of these 43 can have serious side effects, [Bailey, D.G. Canadian Medical Association Journal, published online Nov. 26, 2012].

So if you are on conventional/prescription drugs, make sure to ask your health care provider before including grapefruit in your diet. And if you are not, make sure to enjoy this wonderfully nutritious fruit!

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