The Mediterranean diet has been shown to have multiple favorable health effects, including reducing the risks of heart disease and stroke. The diet features high intake of vegetables and fruits and low consumption of processed food and saturated fat. Most of the studies that have attempted the evaluate whether adherence to the Mediterranean diet lowers breast cancer risk have not found a direct correlation. However, the same studies have reported that aspects of the diet are associated with reduced risk. On the other hand, there are some foods commonly consumed by Italian women that are associated with increased breast cancer risk. While the overall pattern of nutrition represented by the Mediterranean diet promotes good health, vegetables and fruits should be selected for their demonstrated chemopreventive effects.
Description of the Mediterranean diet
The Mediterranean diet is based on the diet of people living in Spain, southern Italy, and Greece in the post-World War II period when food was for the most part abundant, but modern farming and food production methods were not yet widespread. In addition, the people engaged in a great deal of physical activity in their daily lives. Only a minority of the people in the region could be said to adhere to this diet today.
The diet has been associated with a lower levels of LDL cholesterol (the "bad" cholesterol), triglycerides, blood pressure, and blood sugar, according to a variety of studies. This translates into lower likelihoods of metabolic syndrome, obesity, type 2 diabetes, and heart disease.
The Mediterranean diet can be described with a food pyramid, with the following layers (starting with the foods consumed most often):
- Vegetables, fruits, olives and olive oil, dry beans and other legumes, nuts and seeds, herbs and spices
- Wheat (bread and pasta) (mostly whole grain), rice, and unrefined cereals
- Fish and seafood
- Chicken and other poultry, eggs, cheese, yogurt, wine (mostly red)
- Red and processed meat, sweets and desserts
Note that the Mediterranean diet does not include much butter; bread is served with olive oil instead. Food is not deep fried. Nuts are not candied, honey-roasted, smoked or heavily salted. Clearly, the Mediterranean diet does not emphasize many Italian dishes popular in the U.S., such as pizza, spaghetti with meatballs, fettuccine Alfredo or other pasta with rich sauces, veal parmigiana, calzonies and tiramisu.
Mediterranean diet can translate into lower breast cancer risk
Studies that have attempted to determine whether conforming to the Mediterranean diet reduces breast cancer risk have produced conflicting results. However, there is some evidence that strict adherence to the diet could be beneficial:
- A 2016 Italian study reported that adherence to the Mediterranean dietary pattern was associated with lower risk of breast cancer recurrence in women with early invasive breast cancer. Beta-carotene levels were most strongly correlated with adherence to the diet.
- A 2015 Spanish study reported that the Mediterranean dietary pattern was related to a lower risk of breast cancer in women aged 60 to 80 years and at high risk of cardiovascular disease, especially women whose diets were supplemented with extra-virgin olive oil.
- A carefully designed 2014 study reported that the Mediterranean dietary pattern was related to a lower risk of breast cancer, especially triple negative disease.
- A large 2013 Swedish prospective study found no association between adherence to the Mediterranean dietary pattern and risk of breast cancer overall, or with specific breast tumor characteristics.
- A large European prospective study investigated the association between adherence to the Mediterranean diet and breast cancer risk among 335,062 women who were followed for an average of 11 years. Adherence to a Mediterranean diet excluding alcohol was found to be associated with modestly reduced breast cancer risk in postmenopausal women, and this association was stronger in hormone receptor negative tumors.
- A case-control study investigated whether the degree of adherence to the Mediterranean diet influenced breast cancer risk among Greek-Cypriot women. No direct link was found between conformity to the Mediterranean diet and breast cancer risk. On the other hand, higher consumptions of vegetables, fish and olive oil each were independently associated with reduced breast cancer risk.
- An Italian prospective study was designed to investigate associations between diet and breast cancer reported that women in the highest fifth of vegetable consumption (including all types of vegetables) were found to have a 35% lower risk of breast cancer compared to women in the lowest fifth. When types of vegetables were considered separately, women in the highest fifth of leafy vegetable intake were found to have a 30% lower risk of breast cancer than those in the lowest fifth. Leafy vegetables consumed in Italy include lettuce, spinach, kale, and parsley, as well as greens such as arugula. Women in the highest fifth of fruiting vegetable intake were found to have a 25% lower risk of breast cancer than those in the lowest fifth. Fruiting vegetables, which are grown for their fruits rather than their leaves, seeds or roots, include tomatoes, hot and sweet peppers, and eggplant. On the other hand, no association with breast cancer risk was found for fruit intake.
- A UK study compared the risk of developing breast cancer associated with consumption of either a Mediterranean dietary pattern or a healthy dietary pattern (conforming to the World Health Organization Healthy Diet Index). No significant associations were found between either the Mediterranean dietary pattern or the healthy dietary pattern and risk of breast cancer. In premenopausal women, there was a some evidence that increasing compliance with the Mediterranean diet was associated with lower risk of breast cancer, but the results were not statistically significant. In postmenopausal women, no clear trends were observed.
Dietary pitfalls for Mediterranean women
If vegetables, fish and olive oil appear to be the elements of the Mediterranean diet most associated with reduced breast cancer risk, what are the elements that are not favorable? Based on research in other populations, alcohol (including red wine) and cheese are associated with increased breast cancer risk. However, for strict adherents of the diet, modest amounts of cheese and wine should not greatly increase risk.
However, there are dietary choices or patterns that appear to increase breast cancer risk in Mediterranean women. In other words, women who conform to some degree to the Mediterranean diet can undermine the favorable effects with other food choices. High refined carbohydrate intake is associated with increased breast cancer risk in Italian women. For example, one Italian study reported that women in the highest third of intake of desserts (including cookies, brioches, cakes, pastry puffs and ice-cream) or sugars (including sugar, honey, jam, marmalade and chocolate) had 1.2 times the risk of breast cancer as those in the lowest third.
Another Italian study also found that risk of breast cancer increased with increasing consumption of bread, pasta and refined sugar. In addition, the same study found that breast cancer risk was increased with increasing consumption of pork, processed meats and potatoes.
The Mediterranean diet is a very good starting point. However to reduce breast cancer risk, it is best to be even more selective of foods to include in your diet. All vegetables and fruits in the Mediterranean diet are not equal. For example, fennel is less cancer-preventive than kale and pears are less beneficial than apples. This is the point of our recommended foods and foods to avoid lists, which have been selected based on the evidence in studies to date. Please also see our article on how to optimize your breast cancer diet for information on what to eat during all stages of treatment and recovery.