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Mediterranean diet and breast cancer risk: informative JAMA news release includes ample caveats


4 Star

Mediterranean diet plus olive oil associated with reduced breast cancer risk

Our Review Summary

Olive oilThis news release reports on the findings of a large European study, published in JAMA Internal Medicine, asking whether older women participants following a Mediterranean Diet, supplemented with either extra-virgin olive oil (EVOO) or nuts, experienced a different rate of breast cancer than women receiving straightforward dietary advice.  The outcome showed that those supplemented with EVOO experienced fewer cases of breast cancer than did the control group or the group supplemented with nuts.

Overall, the release does an excellent job of summarizing the results of the study and putting the evidence in context. The study’s numerous limitations are addressed, and the release also quotes from an accompanying editorial that provides a valuable independent perspective. The release would have benefited from inclusion of absolute risk numbers and some acknowledgment that the diet studied here could be costly to follow.


Why This Matters

Breast cancer is the most common cancer in women.  If the risk of this disease can be lowered by simply altering one’s diet, it would represent a safe, non-pharmacological approach to improving the public’s health.


Does the news release adequately discuss the costs of the intervention?

Not Satisfactory

The release makes no mention of the cost of the supplemented diets compared to what might be expected for a normal daily diet.  Some brands of extra-virgin olive oil can cost considerably more, comparatively, than other available cooking oils.  And you’d have to buy lot of olive oil to match this diet — participants received a whopping 1 L per week per family. Other foods in the Mediterranean diet (e.g. fish and nuts) are also relatively expensive. So the release fails at this category, although it is a minor failure in this case considering the relative strength of the rest of the release.

Does the news release adequately quantify the benefits of the treatment/test/product/procedure?

Not Satisfactory

The release points out that the participants following the Mediterranean Diet supplemented by EVOO experienced a 68 percent lower relative risk of breast cancer than did the control group. While that’s one way to report the findings, we always ask that stories also include a measure of the absolute risk, which provides important additional information to help readers gauge the size of the benefit. These absolute risk figures were reported in the study abstract and could have easily been included in the release as well. The researchers found breast cancer rates of 1.1 per thousand people per year in the Med Diet plus EVOO group, 1.8 per thousand people per year in the Med Diet plus nuts group, and 2.9 per thousand people per year in the control group.

Does the news release adequately explain/quantify the harms of the intervention?

Not Applicable

Consuming both nuts and olive oil have been shown in numerous studies to be a positive asset to the regular diet.  And yet these foods are very calorie-dense, and so one wonders if consuming so much of them could increase the risk for weight gain, which is in turn associated with breast cancer risk. But the release’s lack of discussion on that point shouldn’t be enough for a Not Satisfactory rating — we’ll rule it Not Applicable.

Does the news release seem to grasp the quality of the evidence?


This release described a large, multi-center, randomized trial where those analyzing the data were blinded to information that might influence their findings.  It gave ample information about the study design, it’s relationship to the larger cardiovascular study from which it is derived, and the size, scope, age and body mass of the participants.  The release also does a good job following the research paper’s example of delineating the weaknesses of the study. It even quotes the cautionary language included in an accompanying editorial.

Does the news release commit disease-mongering?


This release offers no evidence of disease-mongering.

Does the news release identify funding sources & disclose conflicts of interest?

Not Satisfactory

The release only offers the following statement as an endnote: “Authors made conflict of interest and funding/support disclosures. Please see the article for additional information, including other authors, author contributions and affiliations, financial disclosures.”  The paper itself points to numerous connections between the researchers and sponsors which would have an obvious vested interest in the study’s outcome.  These include grants as well as free supplies of the foods supplemented in the study.  While this doesn’t call the findings into question, disclosing this information in a release of this type provides transparency that readers appreciate and should expect.

Does the news release compare the new approach with existing alternatives?

Not Applicable

The release offers no real alternatives to the diets studied but it is reasonable to assume that readers can compare these examples with their own diets and make decisions accordingly.

And while there are other approaches to cancer prevention that arguably could have been discussed (screening mammography, for example), we don’t really think a release about a diet study should be expected to address those approaches.

Does the news release establish the availability of the treatment/test/product/procedure?


It’s clear from the release that the foods in the Mediterranean diet are widely available. However, it might be harder to find certain component foods like fish, fresh fruits and vegetables, and extra virgin olive oil in some places in the U.S. (i.e. “food deserts”). The release could have acknowledged this.

Does the news release establish the true novelty of the approach?


The release establishes that the effects of diet on breast cancer risk have been studied previously with this line: “Diet has been extensively studied as a modifiable risk factor in the development of breast cancer but epidemiologic evidence on the effect of specific dietary factors is inconsistent.”

Total Score: 5 of 8 Satisfactory


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