"Killer" grapefruit?

Got Taste?

A few months ago, in a post on medical journalism, I noted: “The unstated assumption … is that ‘scaring the bejesus out of people’ is a recognized journalistic practice when it comes to health news.” This post describes a medical case in which grapefruit played a minor role. The next post illustrates how the media turned this innocent, everyday item into an object of fear.


Image source: J. Tome

The British medical journal The Lancet recently published the case report of a 42-year old woman who developed pain in her low back, left buttock, and left leg after a 90-minute car trip. The next day, when her leg had turned purple, she went to an emergency room. She was light headed, short of breath, and had difficulty walking. Her medications included Levothyroxine (Synthroid) for low thyroid levels and birth control pills, the estrogen/progestin combination type.

On examination, the woman was found to have a blood clot in her leg, a deep-vein thrombosis (DVT) that extended from her hip to her calf. What makes this story of interest to physicians is not the diagnosis, which was obvious, but the etiology: What caused this woman to have a DVT?

The patient had been on a three-day grapefruit diet, drinking eight ounces of grapefruit juice in the morning. She had rarely consumed grapefruit in the past. This fact was not known until after the patient was successfully treated and released. She happened to mention it as she was being discharged.

Was it the grapefruit?

The grapefruit diet has been around since the 1930s. It’s based on the erroneous idea that there’s a magical ingredient in grapefruit that causes the body to burn fat when you eat protein and grapefruit in the same meal. If you only eat 800 to 1000 calories a day – it’s a very strict diet – chances are you’ll lose weight. But you’ll gain it right back once you return to normal eating.

Could the grapefruit diet have caused this patient’s blood clot?

Grapefruit contains a flavonoid, naringin, that can interfere with the action of certain medications, as I mentioned in my last post. But grapefruit alone does not cause clotting.

One of the substances that grapefruit can interfere with is ethinyl estradiol, an ingredient in contraceptive pills. The interference happens indirectly. Normally an enzyme in the body breaks down (metabolizes) ethinyl estradiol, but grapefruit interferes with the enzyme. When the estradiol isn’t broken down, it can accumulate to unsafe levels. Too much estradiol can cause blood clots. This is a known, but uncommon, side effect of contraceptive pills.

Deep Vein Thrombosis

Deep vein thrombosis (DVT). Image source: The Internet Encyclopedia of Science

When we examine this case a little more closely, it turns out this woman had a lot of things going on besides drinking grapefruit juice. She had an inherited blood clotting disorder called Factor V Leiden thrombophilia. She had May-Thurner Syndrome, which compresses the vein to the left leg between an artery and a vertebra in the low back.

People with May-Thurner Syndrome are three times as likely to develop deep vein thrombosis (DVT) in the left leg as the right leg, and this woman’s DVT was in her left leg. As mentioned, contraceptive pills by themselves have DVT as a possible side effect. And she had been sitting in a car for 90 minutes just before the symptoms began. This in itself is a risk for blood clots. It’s known as economy-class syndrome.

The woman was treated to relieve the clot and was able to leave the hospital that same evening. As I mentioned, her consumption of grapefruit was not discovered until she was discharged. The doctor overseeing the case subsequently did some research and concluded that the grapefruit may have been the last straw that “tipped the balance.” The Lancet article concludes: “[T]his was a rare occurrence, and … grapefruit is not necessarily a danger to women taking the combined [contraceptive] pill.”

In an interview, the patient’s doctor said:

[T]his woman’s story is so unique it should not discourage people in any way from eating grapefruit. … Grapefruit is not a danger to society. It just happened to be dangerous for this specific person in this specific situation.

Media coverage

How did the media handle this story? It was all about the grapefruit, something anyone might innocently eat — and promptly die. Or at least lose a leg to gangrene. I suppose, to give the media the benefit of the doubt, they probably saw this as a “teachable moment.” Unfortunately, outright fear of “killer grapefruit” was the wrong lesson.

For details on how bad the media coverage actually was, see the next post.

Related posts:
A matter of taste
How do you taste?
Orange juice and toothpaste
What is a supertaster?
The genetics of supertasting
Are you a supertaster: Do you really want to know?
Are you a supertaster: Look at your tongue
Are you a supertaster: How does PROP Taste to you?
Are you a supertaster: DNA testing
Why do we love high-fat foods?
Do we taste fat?
The taste advantage
Grapefruit and the Pill
This is your brain on sugar — and sugar substitutes
The Pepsi challenge: How beliefs affect what you taste


Lucinda A Grande MD, Raul D Mendez MD, Richard T Krug MD, Evert-Jan Verschuyl MD, Attention–grapefruit! The Lancet, Vol. 373, Issue 9670, p. 1222, April 4, 2009

‘Killer’ grapefruit, Behind the Headlines, April 3, 2009

Grapefruit juice: Can it cause drug interactions? Mayo Clinic

Helen Branswell, Grapefruit, birth control pill interaction may have caused weird blood clot case, The Canadian Press


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