The Mediterranean diet and cardiometabolic risk factors: a review of effects and contextual influences

The Mediterranean Diet (Med Diet) has long been shown to be associated with lower cardiovascular mortality in epidemiological studies. However, the direct effect of the dietary pattern on cardiovascular risk factors is less clear. Furthermore, the effect of Med Diet interventions in non-Mediterranean populations on cardiovascular and metabolic risk is variable. A Cochrane Review in 2019 concluded there was low to moderate evidence of a modest benefit but noted that there were still ongoing trials. Since 2019, there have been a number of published trials that have not shown a benefit of the Med Diet over other interventions or usual care. It is possible that dietary factors such as quality or quantity of carbohydrate and energy restriction are more important factors, along with the degree of weight loss, than the Med Diet itself. There are also many other factors that influence the uptake and effectiveness of the Med Diet in populations that have a different traditional or habitual diet. This review paper examines a selection of 20 Med Diet intervention trials specifically looking at clinical outcomes of glucose metabolism: fasting plasma glucose, HbA1c, development of type 2 diabetes or need for hypoglycaemic medications, with or without other cardiometabolic risk factors. These trials are a mix of randomised controlled trials, crossover studies and cohort studies of greater than 8 weeks duration with more than 25 participants. There is heterogeneity in study designs and outcomes, making comparison difficult, but there is no clear benefit of the Med Diet presented.