Is olive oil key to Mediterranean diet and breast cancer prevention?

Mediterranean Diet, Olive Oil & Breast Cancer Risk

Can a Mediterranean-style diet reduce your risk of breast cancer?

Exciting headlines from the PREDIMED study proclaim potential for major reductions in breast cancer risk, with olive oil seemingly a key factor. Yet other studies portray less clear-cut protection. Therefore, it’s important to step back and look at what differing results among these studies might mean as women seek to find doable choices that could play a role in reducing breast cancer risk.

Med Diet & Breast Cancer – Big Picture

The PREDIMED study that is adding to enthusiasm over Mediterranean diets shows a 51% lower risk of post-menopausal breast cancer in the two groups of women assigned to Mediterranean eating patterns compared to women in a control group advised to try to reduce fat consumption (which they accomplished with limited success). Women in PREDIMED were all 60 to 80 years old with either type 2 diabetes or at least three major heart disease risk factors, and virtually all were overweight or obese.

An analysis combining results of several population studies that included a broader range of women and followed them for longer periods shows no link between how closely women followed a Mediterranean diet and breast cancer incidence among the most reliable type of studies (prospective cohort studies). Many of these studies involved women living outside the Mediterranean area, so maybe that lack of association reflects eating habits that weren’t all that “Mediterranean” even in women with the most Mediterranean-style diets in those studies. In an observational study that tracked women in Mediterranean and non-Mediterranean European countries for 11 years, those whose diets most closely resembled a Mediterranean diet compared to other women in their country had 7% lower risk of post-menopausal breast cancer than those with the least Mediterranean-style diets. Looking only at Greek women from this large study, risk of postmenopausal breast cancer was 41% lower among those with the most Mediterranean-style eating habits.

How Mediterranean are Your Eating Habits?

We may think of a Mediterranean diet as one that involves eating lots of dishes typical of cuisine in Greece, Italy and other Mediterranean countries. But especially as those dishes get translated in countries like the U.S., that’s not really the key to a Mediterranean diet as it’s defined for health-related studies. In fact, your eating habits can rate high on the scoring systems used in this research with nary a sign of oregano, eggplant or feta cheese.

Most U.S. studies use the Alternate Mediterranean Diet Score, developed to work more appropriately among a non-Mediterranean population like the U.S. People in a study get points for how their eating compares to that of others in the study, with points for eating more of the foods characteristic of this eating pattern and for eating less of the foods typically eaten in only limited amounts in the classic Mediterranean diet.

 

Mediterranean Diet scoring system used in research

(Alternate Mediterranean Diet Score developed by Fung and colleagues, see reference list below)

 

Comparing diets that earn a “high” rating in the U.S. compared to traditional Mediterranean populations, “high” amounts of legumes (dried beans and peas), nuts and fish are much lower. For example, in the U.S., simply eating more than 1½ servings of legumes per week is high, while a true Mediterranean diet includes them every day or two. Likewise, eating nuts more than once a week might count as high in the U.S., while classic definitions of a Mediterranean diet include an ounce of nuts at least every day or two. Fish consumption tends to be higher in many parts of the Mediterranean, so relatively “high” consumption in the U.S. would not rank as very high in most Mediterranean populations. If these foods provide part of the health benefits associated with Mediterranean diet, that may be part of why high scores vary in the link with health outcomes seen among different studies.

One of the key characteristics of a Mediterranean diet is use of olive oil as the primary source of added fat. In Spain, consumption of over four tablespoons of olive oil per day is common. In other Mediterranean countries, although olive oil is the standard choice, two or three tablespoons daily may be more common. Regardless, “high” consumption is considerably higher than “high” use in the U.S.

Is It the Olive Oil?Olive oil can be a healthy eating choice in Mediterranean diets

Research regarding olive oil’s relationship to heart health is strong, but is still relatively limited regarding cancer risk. In the PREDIMED study noted above, in which women assigned to Mediterranean diet eating patterns were less likely to develop postmenopausal breast cancer than women in the control group, women assigned to a Mediterranean diet with a specific target for extra virgin olive oil consumption showed particularly low risk.

Moreover, regardless of group assignment, women who got the greatest proportion of their calories from extra virgin olive oil had a far lower risk of breast cancer than those with the least. For each 5% of calories coming from extra virgin olive oil, risk of postmenopausal breast cancer was reduced by 28%.

Several observational population studies that followed people for even longer periods link use of olive oil with lower risk of cancer, possibly including lower risk of breast cancer and digestive tract cancers. Among postmenopausal women in Mediterranean countries within the EPIC study, greater olive oil consumption was not linked to overall breast cancer incidence, but a potential link to lower risk of estrogen and progesterone receptor-negative tumors was found. Analyses combining the results of several studies do show lower risk of breast cancer among those with highest olive oil consumption compared to lowest consumers. However, only some of these population studies are the type (prospective cohorts) that provides the most solid data, with many the case-control type that is harder to interpret. Moreover, although some of these studies adjusted for factors that could influence the association of olive oil with breast cancer risk, some did not adjust the results for important factors like tobacco use and alcohol.

More than three-fourths of the fat in all types of olive oil is monounsaturated fat, which many people assume accounts for olive oil’s link to heart health. However, the type of olive oil may be relevant to both heart health and lower cancer risk. Virgin & extra virgin olive oils, which are not refined, maintain higher levels of:

  • Phenolic compounds, natural phytochemicals found in many plant foods. Those in olive oil that are the focus of current research include oleuropein and oleocanthal, and two others formed from them, tyrosol and hydroxytyrosol. These are a different set of phenolic compounds than those you get from vegetables, fruits and whole grains.
  • Tocopherols, compounds related to Vitamin E that may also offer protective effects.

Cell studies suggests that the compounds in extra virgin olive oil can decrease growth and increase self-destruction of cancer cells, and may offer other cancer-protective effects.  Animal studies show potential protection through epigenetic effects (accomplished by “turning on” protective genes and “turning off” genes that lead to cell damage), support of antioxidant defenses, and anti-inflammatory effects.

Or Is It Food Choices That Come Along with Olive Oil?Mediterranean diets are plant-based diets high in vegetables

It’s possible that these population studies link greater olive oil consumption with lower cancer risk because olive oil use tends to go hand in hand with an overall healthy pattern that involves eating more vegetables and other healthful plant foods.

Examining data from the PREDIMED study as a whole (men and women), those assigned to the Mediterranean diet group with a focus on increasing extra virgin olive oil did not only increase use of this oil. They also decreased use of refined olive oil even more than the control group striving for a low-fat diet. In other words, more than half of their increase in extra virgin olive oil was achieved by using it to replace more refined olive oil. Since they did not increase total calorie consumption, clearly some other changes in eating habits also occurred as fat consumption increased.

 

More Olive Oil Without More Calories

Olive oil’s association with reduced breast cancer in PREDIMED and in the observational studies reflects a greater proportion of calories coming from olive oil, with fewer calories from other foods. Since overweight increases risk of postmenopausal breast cancer (and nine other cancers), it’s important that a shift to greater use of extra virgin olive oil does not bring an unwanted increase in total calories.

 

Mediterranean-style eating patterns are linked with multiple aspects of health, and reasonable evidence suggests that these choices could play a role in reducing risk of breast and some other cancers.

Bottom Line:

If you think healthy eating is boring or flavorless, look to Mediterranean cuisines for inspiration! But if you don’t yearn for Mediterranean flavors or foods — at least not all the time – note that the characteristics that define this eating pattern where it is linked with lower risk of cancer and heart disease have nothing to do with specific dishes. This is a plant-focused eating pattern that limits red meat and sweets, and for those who aren’t vegetarians, includes fish regularly. Olive oil as a major portion of added fat also seems a health-wise choice. But don’t give it a health halo. If you add an extra 100 to 200 calories by using more extra virgin olive oil, make sure that you reduce fatty and processed meat, refined grains, sweets and unhealthy types of added fat, since there is no question that excess body fat increases risk of post-menopausal breast cancer.

If you find this info helpful, please share it on Facebook, Twitter or through an email to a friend or colleague.

Wondering which elements of a Mediterranean diet show most consistent potential for reducing cancer risk and promoting heart health?

For a free tip sheet with 5 doable steps:  Click Here.

Helpful Resources:

Learn more about how to create Mediterranean-style eating habits from Oldways Preservation Trust.

To learn more about choosing and using olive oil, check Oldways’ Olive Oil 101 and Olive Oil Everyday from the North American Olive Oil Association.

To get the big picture on steps with the most solid evidence about reducing risk of breast cancer, see the American Institute for Cancer Research.

References:

Toledo E, Salas-Salvadó J, Donat-Vargas C, et al. Mediterranean Diet and Invasive Breast Cancer Risk Among Women at High Cardiovascular Risk in the PREDIMED Trial: A Randomized Clinical Trial. JAMA Intern Med. 2015; 14:1-9.

Schwingshackl L and Hoffmann G. Adherence to Mediterranean diet and risk of cancer: a systematic review and meta-analysis of observational studies. Int J Cancer. 2014; 135(8):1884-97.

Buckland G, Travier N, Cottet V, et al. Adherence to the mediterranean diet and risk of breast cancer in the European prospective investigation into cancer and nutrition cohort study. Int J Cancer. 2013; 132(12):2918-27.

Fung TT, McCullough ML, Newby PK et al. Diet-quality scores and plasma concentrations of markers of inflammation and endothelial dysfunction. Amer J Clin Nutr 2005, 82(1):163-173.

Buckland G, Travier N, Agudo A et al. Olive oil intake and breast cancer risk in the Mediterranean countries of the European Prospective Investigation into Cancer and Nutrition study. Int J Cancer. 2012; 131(10):2465-9.

Psaltopoulou T, Kosti RI, Haidopoulos D, et al. Olive oil intake is inversely related to cancer prevalence: a systematic review and a meta-analysis of 13,800 patients and 23,340 controls in 19 observational studies. Lipids Health Dis. 2011;10:127.

Pelucchi C, Bosetti C, Negri E et al. Olive oil and cancer risk: an update of epidemiological findings through 2010. Curr Pharm Des. 2011; 17(8):805-812.

Casaburi I, Puoci F, Chimento A, et al. Potential of olive oil phenols as chemopreventive and therapeutic agents against cancer: a review of in vitro studies. Mol Nutr Food Res. 2013; 57(1):71-83.

Escrich E, Moral R, Solanas M. Olive oil, an essential component of the Mediterranean diet, and breast cancer. Public Health Nutr. 2011; 14(12A):2323-2332.

2 Comments

  1. […] Mediterranean diet, olive oil & breast cancer risk.  Another study adds to the growing evidence that eating a Mediterranean-style diet helps prevent disease. In this study (Predimed), women eating a Mediterranean diet reduced post-menopausal breast cancer risk by 51% compared to women in a control group.  Karen Collins of the American Institute for Cancer research takes an in-depth look at this study, explaining how research typically characterizes Mediterranean-style diets by the amount of vegetables, fruits, legumes, nuts, whole grains, with olive oil as the primary source of added fat,  and limited red meats or processed meats. The Predimed study found that olive oil consumption offered additional protection against cancer.  Collins suggests that it’s possible that studies linking greater olive oil consumption with lower cancer risk may be “because olive oil use tends to go hand in hand with an overall healthy pattern that involves eating more vegetables and other healthful plant foods” and stressed that it’s important that increased olive oil consumption doesn’t increase overall calories, as being overweight is an established risk factor for breast cancer. (Karen Collins, reporting on JAMA Internal Medicine, Nov 2015.) […]

  2. […] Mediterranean diet is a plant-focused diet. Emphasis is on vegetables, fruits, whole grains and pulses (like dried […]

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Meet the author/educator

Karen Collins
MS, RDN, CDN, FAND

I Take Nutrition Science From Daunting to Doable.™

As a registered dietitian nutritionist, one of the most frequent complaints I hear from people — including health professionals — is that they are overwhelmed by the volume of sometimes-conflicting nutrition information.

I believe that when you turn nutrition from daunting to doable, you can transform people's lives.

Accurately translating nutrition science takes training, time and practice. Dietitians have the essential training and knowledge, but there’s only so much time in a day. I delight in helping them conquer “nutrition overwhelm” so they can feel capable and confident as they help others thrive.

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