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The Mediterranean diet lowers risk of developing cancer, particularly colorectal cancer.

Bloomfield HE, Koeller E, Greer N, et al. Effects on health outcomes of a Mediterranean diet with no restriction on fat intake: A systematic review and meta-analysis Ann Intern Med. 2016; 165: 491-500.

Review question

Do adults who follow the Mediterranean diet have better health outcomes, including lower risk of death, lower risk of being diagnosed with a chronic disease, or lower risk of disease progression in those with diabetes, cardiovascular disease, cancer, hypertension, cognitive impairment, arthritis, or kidney disease.

Background

The Mediterranean diet is a mostly plant-based diet with a high ratio of monounsaturated fats (healthy fats). Previous studies that included people who followed a Mediterranean diet showed a potential for a lower risk of death during the study period, and other positive health outcomes.

How the review was done

• This is a review of 44 medium quality studies including over 2 million participants, published between 2001 and 2015. Only 2 included studies were randomized controlled trials.
• 26 studies included both men and women, 14 studies included women only and 4 studies included men only. The average age of participants was 56.5 years, ranging from 36-83 years. 20 studies were conducted in the USA/Canada, 20 in Europe, and 4 in Asia/Australia.
• All studies compared participants who followed a Mediterranean diet to those who did not. For this review, the Mediterranean diet was anything that included at least two of the following: high healthy fat ratio (ex. Use of olive oil), lots of fruits and vegetables, lots of legumes, lots of grains and cereals, moderate red wine, moderate dairy intake, small amounts of meat or meat products, and high amounts of fish.
• The researchers included information on risk of death, risk of being diagnosed with a disease, and risk of disease progression in those with diabetes, cardiovascular disease, cancer, hypertension, cognitive impairment, arthritis or kidney disease.

What the researchers found

Based on the included studies, the Mediterranean diet had no impact on risk of death, risk of developing breast cancer or cognitive functioning. The Mediterranean diet does lower risk of all cancers, and colorectal cancer. There was not enough information to draw conclusions about other health outcomes.

Conclusion

The Mediterranean diet may lower risk of all cancers, particularly colorectal cancer but does not decrease one’s risk of death. More high-quality research is needed to understand the effect of the Mediterranean diet on other health outcomes.