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Mediterranean Diet Slashed Breast Cancer Risk
Diet rich in veggies and fish plus abundant extra virgin olive oil won a rare clinical trial

09/18/2015
Score another one for the famed Mediterranean diet.

By "Mediterranean diet”, nutrition-health researchers mean one that embodies the dining traditions of rural Greece, Italy, and Spain.

The idealized Mediterranean diet features vegetables, fruits, beans, poultry, fish, cheese, extra virgin olive oil, and small amounts of whole grains.

We've covered the health effects of the Mediterranean diet pretty extensively … see these articles and the links in them: Mediterranean Diet: Women's Anti-Aging Ally?, Mediterranean Diet + EVOO Cut Diabetes Risk by 40%, and Women Fare Very Well on Mediterranean Fare.

Sadly, the diets of people around the Mediterranean Ocean have been degraded by an influx of cheap processed foods.


The last part of that article's title matches the key finding of a rare clinical trial in women, which probed the anti-cancer potential of the Mediterranean diet.

Before examining the encouraging results in detail, let's review what's known about the Mediterranean diet and cancer.

Mediterranean diet: An anti-cancer ally?
Scientists at Austria's University of Vienna recently reviewed 33 studies that had looked for links between the Mediterranean diet and cancer risk.

And the Austrian team came to some specific conclusions: "adherence to a Mediterranean diet is associated with a significant reduction in the risk of overall cancer mortality (10%), colorectal cancer (14%), prostate cancer (4%) and aerodigestive [mouth, nose, throat, esophagus, and windpipe] cancer (56%).

Oddly, they failed to similarly quantify the reduction in breast cancer risk seen in several large epidemiological studies (Pelucchi C et al. 2010; Escrich E et al. 2011; Psaltopoulou T et al. 2011; Casaburi I et al. 2013; Escrich E et al. 2014).

At the time of their evidence review, the Austrians found only epidemiological studies ... no controlled clinical trials.

That gap came as no surprise, because it's very difficult to conduct trials that compare the effects of diets on diseases that take decades to develop.

Fortunately, a new clinical trial succeeded in comparing the Mediterranean diet against a standard diet with regard to breast cancer risk.

Mediterranean Diet slashed breast cancer risk
Spanish researchers conducted the rare new clinical trial (Toledo E et al. 2015).

The encouraging results were published in a journal from the American Medical Association (JAMA Internal Medicine).

The study was part of the large PREDIMED (Prevención con Dieta Mediterránea) trial, designed to test the effects of the Mediterranean diet on the risk for cardiovascular disease.

The PREDIMED study involved 4,282 overweight women (average age 68) deemed at high risk for cardiovascular disease.

The women had an average body mass index of 30.4, which falls just over the line that defines someone as obese.

Most of them had undergone menopause before the age of 55 and less than three percent used hormone therapy.

The women were randomly assigned to follow one of three diets for five years:
  • Mediterranean diet + extra EVOO – 1,476 women
  • Mediterranean diet + extra nuts – 1,285 women
  • Control diet with advice to reduce their intake of fat – 1,391 women
The women in the Mediterranean diet + extra EVOO group (and their families) consumed one liter (34 ounces) of EVOO per week.

The women in the Mediterranean diet + nuts group (and their families) consumed 30 grams (just over one ounce) of nuts daily: 15 grams of walnuts, 7.5 grams of hazelnuts, and 7.5 grams of almonds.

Over an average of nearly five years, the authors identified 35 confirmed new cases of malignant breast cancer among the participants. 

Compared with women on the control diet, the women assigned to the Mediterranean diet with added extra virgin olive oil (EVOO) were 68 percent less likely to develop malignant breast cancer.

In contrast, in the women assigned to the Mediterranean diet with added nuts showed only a "non-significant” risk reduction compared with women in the control group.

Olive oil and cancer: An overview
Several recent evidence reviews support the idea that extra virgin olive oil is a powerful ally against breast cancer.

According to the Spanish authors of a review published last year, "Abundant data have attributed a potentially chemo-preventive effect for extra-virgin olive oil (EVOO), the main source of fat in the Mediterranean diet, which is associated with low incidence and mortality rates from chronic diseases such as breast cancer.” (Escrich E et al. 2014)

But it's critical to make the distinction between extra virgin olive oil (EVOO) and the two other grades (virgin and pure).

Only extra virgin olive oil is rich in antioxidants, which are largely (virgin) or completely (pure) refined out of the two other grades.

These compounds, known as tyrosols, are virtually unique to olives, and unusually powerful compared with the antioxidants in other fruits and vegetables.

In a test tube experiment published earlier this year, one of these tyrosol antioxidants – called oleocanthal – killed a variety of human cancer cells, but did no lasting harm to healthy cells (LeGendre O et al. 2015).

Limitations of the new trial
As with most studies, this one had a number of limitations that prevent a definitive conclusion.

First, the number of new breast cancer cases was low, which limits the statistical strength of the results.

Second, the study's design precluded a definite conclusion as to whether the risk reduction was attributable mainly to EVOO or to its consumption within the context of the Mediterranean diet.

However, given the evidence of extra virgin olive oil's apparent anti-cancer effects, and the markedly different results for the group assigned to the Mediterranean diet plus nuts, it seems quite likely that EVOO exerts particularly powerful ant-cancer effects.

Of course, as the authors of the new trial said, "these results need confirmation by long-term studies with a higher number of incident cases.” (Toledo E et al. 2015)

Mitchell H. Katz, M.D., a deputy editor of JAMA Internal Medicine, made two key points about the new trial's results (Katz MH 2015):

"Of course, no study is perfect. Still, consumption of a Mediterranean diet, which is based on plant foods, fish, and extra virgin olive oil, is known to reduce the risk of cardiovascular disease and is safe.”

"It may also prevent breast cancer. We hope to see more emphasis on Mediterranean diet to reduce cancer and cardiovascular disease and improve health and well-being.” 

Based on a large amount of prior evidence favoring the Mediterranean diet, we couldn't agree more!


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