by James Channing Shaw, MD
There is something you should know about grapefruit. It could change your life.
One week after Mr. Andersen (patient’s name changed) started drinking grapefruit juice every morning, his wife noticed a difference. He had very little interest in sex. At first he passed it off as aging variation, but it persisted into a second week. He had no libido whatsoever. Never before had he experienced problems with low libido or erectile dysfunction. He eventually clued into the grapefruit juice, stopped drinking it, and after two weeks, was ‘back’, just like the ads in the subway.
I knew about grapefruit’s role in altering drug metabolism in the body, but couldn’t find any studies suggesting a direct hit on testosterone, the main determinant of sex drive. Something in that grapefruit juice must have interfered with Mr. Andersen's testosterone for him to have such a rapid response and recovery.
Serendipitously, one month later, I read an article in the British Journal of Cancer(BJC) of a study showing that women who consumed as little as ¼ of a grapefruit per day had a 30 per cent higher risk of developing breast cancer than those who didn’t. This risk was as high as from taking HRT (hormone replacement therapy). The culprit in HRT is estrogen, well known to increase breast cancer risk. Perhaps estrogen was the link to Mr. Andersen's grapefruit scare. It made sense. I probed more.
It turns out there are strong links between grapefruit and estrogen. First, grapefruit contains estrogen-like compounds called flavanoids, also found in green tea and soy products. Flavanoid effects are identical to those of synthetic estrogen, and if you give a man estrogen, his libido drops to near zero.
The other link is the drug metabolism effect. Grapefruit juice is known to inhibit the breakdown of estrogen as well as many drugs, the most notable being cholesterol-lowering drugs called statins. A single six-ounce glass of grapefruit juice is enough to raise blood concentrations of statins.
There is more. In 2007, a study in Nutrition and Cancer found that daily intake of ¼ of a grapefruit increased natural levels of estrogens by about 30 per cent in post-menopausal women. When researchers looked for a link between grapefruit and breast cancer, the 2007 BJC study showed a 30 per cent increase, but a subsequent letter to the editor and a 2009 study in Cancer Causes & Control showed no increased estrogen or cancer risk with grapefruit consumption.
More research is needed to prove the cancer link, but grapefruit’s potential effect on estrogen seems probable.
One thing is certain: testosterone drives libido, and estrogen turns it off. It is highly plausible that a widespread estrogen-like phenomenon from grapefruit juice has been overlooked.
The relationship between grapefruit, estrogen, breast cancer and libido needs further characterization. In the meantime, readers be forewarned.
