Tuesday, 8 April 2008

Grapefruits increase breast cancer risk

A 2007 study of 50 000 post menopausal women found that those that ate ¼ or more grapefruits per day had significantly higher risks of breast cancer. In fact, they had a 30% higher risk than those that didn’t eat grapefruit. This high risk is similar to that of hormone replacement therapy and breast cancer.

Why would grapefruit increase breast cancer risk?

Researchers have known for a while that grapefruits contain a chemical (they’re still not sure which one but they think it’s one called furanocoumarin) that actually prevents an enzyme in your liver and small intestine (called CYP3A4) to break down drugs. That’s why you can’t eat grapefruit or drink grapefruit juice when you’re taking at least a dozen different types of medications. The medication doesn’t get broken down and passes into the blood in really high and dangerous levels.

Some of the more common drugs that are boosted by grapefruit and grapefruit juice include Adalat (used for high blood pressure), Lipitor and Zocor (cholesterol medications), Valium (for anxiety), Zoloft (for depression) and Viagra (for Erectile Dysfunction). Talk to your doctor and pharmacist to learn more about foods you should avoid with your medication!

Turns out that the same enzyme (CYP3A4) is responsible for breaking down estrogen. As a result, when the chemical in grapefruits blocks the enzyme, estrogen builds up in the body. This was validated in the study by the fact that the women who ate ¼ or more grapefruit a day had higher estrogen levels. It’s well established that a high estrogen level is linked to higher risk of breast cancer.

According to the researchers, this is the first time a commonly eaten food has been linked to an increased risk of breast cancer. More research needs to be done, however...the study failed to look at the effect of grapefruit juice (it was lumped together with orange juice).

Grapefruits do have healthful qualities: very high in vitamin C, potassium, fibre. However, the Centre for Science in the Public Interest warns that until more research is done, it may be wise to not eat ½ grapefruit more than 1-2 times a week and drink grapefruit juice only occasionally.

Although the chemical in questions remains a mystery, the prime suspect, furanocoumarin is also found in Seville Oranges and tangelos… you may want to apply the same restraint towards these fruits too.


Grapefruit & Breast Cancer. Nutrition Action Health Letter. October 2007.


Anonymous said...

That's too bad. I like grapefruit. Is it true that grapefruit increase your metabolisme?

Sybil Hebert, RD said...

Thanks for your comment!

Nope, acidic foods (grapefruit or other citrus foods, vinegar, apple cider etc.) don't burn off fat.

These types of diets focus on one "magic" food. If you lose weight, it's because you're not eating as many calories... A meal plan that excludes foods from the major food groups (and focuses on a magic food) should be avoided- it's not sustainable (inevitably, you're going to need or want other foods!) or healthy.

Best way to increase your metabolism? Exercise most days of the week- including both cardio that gets your heart rate up and resistance exercises to use your muscles.