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.
|Vegetables (not including potatoes) Fruits Legumes (dried beans and peas) Nuts (including peanut butter) Whole Grains (ready-to-eat & cooked cereals, bread, cooked grains, popcorn) Fish||+1 point for each of these foods eaten in amounts above average (within a study)|
|Ratio of Monounsaturated Fat to Saturated Fat||+1 point if greater than average (within a specific study)|
|Red meat (beef, lamb, pork) & processed meat||-1 point if amount per day is greater than average|
|Alcohol (1 standard drink = 12 oz beer, 5 oz wine, 1 ½ oz 80-proof liquor)||+1 point for total amounts from 2 drinks/week to 2 drinks/day. (0 points for greater or lesser amounts.)|
Total score from 0 to 9. 9= Most like Mediterranean-style eating pattern.
(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?
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?
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.
Problem: Relying on more bread or pasta as vehicles to increase olive oil actually decreases the proportion of total calories you consume from olive oil.
|1 slice bread with 1 teaspoon olive oil||33% of calories come from olive oil|
Instead: If you enjoy bread or pasta with olive oil, add olive oil and limit portion size to avoid increasing calories.
|2 slices plain bread||160 calories||0% of calories from olive oil|
|2 slices bread each with 1 tsp olive oil||240 calories||33% of calories from olive oil|
|3 slices bread each with 1 tsp olive oil||33% of calories from olive oil|
|1 slice bread with 1 tsp olive oil||120 calories||33% of calories from olive oil|
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.
|Dress a salad with 1 Tablespoon of extra virgin olive oil + lemon juice or vinegar (123 calories)||1/4 c croutons (46 calories) + 2 Tbsp grated cheese or 1 slice crumbled bacon (55 calories) + fat-free dressing (20 calories) = Total 121 calories|
|Vegetables: increase portion by ½ cup and cook with 1 teaspoon olive oil (adds 65 calories)||Large portion of rice, pasta or potatoes – (Reducing portion by ½ cup saves 70-100 calories)|
|1 Tablespoon of extra virgin olive oil in a meal (120 calories)||Large portion of meat – (Reducing portion of lean meat or poultry from 6 oz to 3 oz saves 140-180 calories, more if higher-fat)|
|1 extra Tablespoon extra virgin olive oil in a meal in cooking or flavoring (120 calories) AND Mediterranean-style dessert of fruit (50-80 calories)||Dessert of cookies (4 for 210 calories) or ice cream (1 cup for 270-500 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.
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.
In an upcoming research briefs, we’ll look at what research says about what other aspects of a Mediterranean diet may be important to health. Meanwhile, if you find this info helpful, please share it on Facebook, Twitter or through an email to a friend or colleague.
Learn more about how to create Mediterranean-style eating habits from Oldways Preservation Trust.
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.
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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.
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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.
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