Obesity and the Mediterranean diet: a systematic review of observational and intervention studies G. Buckland 1 , A. Bach 2,3 and L. Serra-Majem 2,4 1 Unit of Nutrition, Environment and Cancer. Epidemiological Research Programme. Catalan Institute of Oncology-IDIBELL, Barcelona, Spain; 2 Mediterranean Diet Foundation, University of Barcelona Science Park, Barcelona, Spain; 3 Department of Public Health, University of Barcelona, Barcelona, Spain; 4 Department of Clinical Sciences, University of Las Palmas de Gran Canaria, Las Palmas de Gran Canaria, Spain Received 23 November 2007; revised 5 May 2008; accepted 7 May 2008 Address for correspondence: G Buckland, Unit of Nutrition, Environment and Cancer, Epidemiological Research Programme, Catalan Institute of Oncology (ICO), Gran Via s/n Km 2,7 Hospitalet. 08907, Barcelona, Spain. E-mail: gbuckland@iconcologia.net Summary World Health Organization projections estimate that worldwide approximately one-third of adults are overweight and one-tenth are obese. There is accumulating research into the Mediterranean diet and whether it could prevent or treat obesity. Therefore, the purpose of this paper was to systematically review and analyse the epidemiological evidence on the Mediterranean diet and overweight/obesity. We identified 21 epidemiological studies that explored the relationship between the Mediterranean diet and weight. These included seven cross-sectional, three cohort and 11 intervention studies. Of these, 13 studies reported that Mediterranean diet adherence was significantly related to less overweight/obesity or more weight loss. Eight studies found no evidence of this association. Exploring the relationship between the Mediterranean diet and overweight/obesity is complex, and there are important methodological differences and limitations in the studies that make it difficult to compare results. Although the results are inconsistent, the evidence points towards a possible role of the Mediterranean diet in preventing overweight/ obesity, and physiological mechanisms can explain this protective effect. Despite this, more research is needed to substantiate this association. Epidemiological studies should use a consistent universal definition of the Mediterranean diet, and address common methodological limitations to strengthen the quality of research in this area. Keywords: Mediterranean diet, obesity, review. obesity reviews (2008) 9, 582–593 Introduction Epidemiological studies have noted increased longevity and reduced morbidity in Mediterranean countries compared with the USA or Northern Europe (1). These health benefits have largely been attributed to the dietary pattern found in these Mediterranean countries in the early 1960s, before its ‘westernisation’. Although there are variations in the components of the traditional Mediterranean diet (MD) (2,3) both between and within Mediterranean countries, the pattern commonly consists of (i) a high consumption of plant-based foods, such as fruit, vegetables, legumes, nuts and seeds and wholegrain cereals; (ii) the use of seasonally fresh and locally grown foods; (iii) olive oil as the main source of dietary lipids; (iv) a frequent but moderate intake of wine (especially red), often with meals; (v) consumption of fresh fish and seafood; (vi) a moderate consumption of dairy products, poultry and eggs and (vii) red and processed meat consumed in low frequency and amounts. Dietary patterns have been studied through component and cluster analysis and many a priori MD indices (4), which have been used to explore the relationship between MD patterns and health parameters, such as mortality or chronic disease risk. As a result, there is increasing epide- miological evidence of the health benefits from the MD, as supported by a systematic review of intervention studies using the MD (5) and a review of the MD and cardiovas- cular diseases (6). There is also growing research on the relation between the MD and obesity, with an increas- ing number of epidemiological studies examining this association. obesity reviews doi: 10.1111/j.1467-789X.2008.00503.x 582 © 2008 The Authors Journal compilation © 2008 International Association for the Study of Obesity. obesity reviews 9, 582–593