Mediterranean Diet and the Metabolic Syndrome

Overview

While there is now undisputable evidence relating elevated plasma low-density lipoprotein (LDL) cholesterol levels to an increased risk of coronary heart disease (CHD), it is being increasingly recognized that a significant proportion of CHD events occur in individuals characterized by a cluster of additional metabolic and physiological perturbations now defined as the metabolic syndrome. Epidemiological and clinical evidence have shown us that nutritional factors, often in conjunction with obesity, play a pivotal role in the pathophysiology of the metabolic syndrome. In that regard, accumulating evidence suggest that a Mediterranean-style diet (MedDiet) may beneficially modify several components of the metabolic syndrome including plasma triglycerides (TG) and high-density lipoprotein (HDL) cholesterol levels, insulin resistance, waist circumference and markers of vascular inflammation. However, the physiological mechanisms underlying the cardioprotective effects of the MedDiet on features of the metabolic syndrome and the importance of body weight reduction in maximizing these effects represent key issues that have yet to be investigated. The general objective of the study is to investigate for the first time in a controlled feeding study the mechanisms and factors underlying the impact of the MedDiet, with and without weight loss on the dyslipidemic features of the metabolic syndrome.

The study has a duration of 35 weeks for each participant. Subjects will be first assigned to a North American control diet that they will consume for five weeks under isocaloric, weight-maintaining conditions. Participants will then consume the MedDiet for 5 weeks, again under isocaloric, weight-maintaining conditions. All foods will be provided to participants during these consecutive 5-week diets. Participants subsequently will then undergo a 20-week weight loss period in free-living conditions during which they will be given advice on how to create a 500 kcal deficit in their daily energy intake. The last phase of the study consists of a second 5-week MedDiet consumed under feeding, weight stabilizing conditions. Metabolic studies and CHD risk factor assessment will be performed at the end of each experimental diets. Metabolic studies include the measurement of in vivo kinetics of apolipoprotein (apo)B-containing lipoproteins including small dense LDL, apoCIII, HDL (apoAI) and C-reactive protein (CRP) as well as indirect measures of cholesterol absorption and synthesis.