Editorial [Hot Topic:Dietary Determinants of the Metabolic Syndrome (Guest Editor: Luc Tappy Co-Editors: Jacques Delarue and Kim-Anne Le)]

Over the past decades, there has been a tremendous rise in the prevalence of obesity, not only in the westernized countries, but all over the world. Although it is well recognized that genetic factors are involved in obesity, this rapid rise is essentially to be attributed to environmental factors; indeed, the human gene pool is unlikely to have changed substantially over such a short period! However, this does not exclude that inside this gene pool some genes may be more expressed or repressed in response to environmental factors, which may in turn lead to metabolic disorders. In this regard, the observation that a Paleolithic diet confers, at least in domestic pigs, a higher insulin sensitivity, a lower blood pressure and a lower C reactive protein level (a surrogate marker of cardiovascular risk) as compared to a cereal-based diet may also be of some interest in an evolutionary perspective [1]. Changes in lifestyle, including increased urbanization, a shift from rural activities - with high energy expenditure - to sedentarity, office jobs and urban environments, increased reliance on motorized vehicles for transportation, increased daily time spent watching TV, and changes in diet, are amongst the numerous factors which can be incriminated in the present rise in obesity observed in Africa and South-eastern Asia. Although these changes in lifestyle occurred several decades earlier in the Westernized countries, present observations suggest that the same factors have been involved in the current epidemics of obesity in North America and in Europe [2]. Obesity is closely associated with several disorders, whose prevalence is also on the rise, including type 2 diabetes mellitus, high blood pressure, dyslipidemia (low HDL cholesterol, high triglycerides) and atherosclerotic heart disease [3,4]. Furthermore, all these conditions frequently occur as clusters in the same individual. Almost 20 years ago, G. Reaven presented evidences from his own work and from the literature that insulin resistance was often present in different distinct diseases, i.e., type 2 diabetes mellitus, dyslipidemia and high blood pressure. He further proposed the hypothesis that insulin resistance was the common factor at the origin of the development of all these conditions, which might explain their clustering [5]. This concept has arisen a lot of interest in both researchers and clinicians. Numerous epidemiological studies have indeed documented the clustering of insulin resistance, T2DM or glucose intolerance, dyslipidemia, high blood pressure and coronary heart disease. The condition, initially referred to as “syndrome X”, has since been renamed as “metabolic syndrome”. A medline search for this entity over the past 10 years yielded over 5000 hits, demonstrating the extent of its appeal to both researchers and clinicians. It is now well documented that this syndrome is highly prevalent in the Westernized countries, and is likely to increase rapidly in other countries as well. The concept, definition and practical use of the metabolic syndrome are not without controversy, however. First, several definitions and diagnostic criteria have been proposed by different associations (Table 1). For the U.S. National Cholesterol Education Program (NCEP/ATPIII) [6], abdominal obesity, dyslipidemia, high blood glucose and high blood pressure are used as exclusive criteria. Since all of these are by themselves risk factors for cardiovascular diseases, detecting their simultaneous occurrence in the same individual most likely identifies individuals at markedly increased risk for heart disease; in a simplistic way, one could say that it is the cardiologist's definition of the syndrome. For the World Health organization (WHO) [7], diabetes or impaired glucose tolerance or insulin resistance is an obligatory criterion, with at least 2 of the other NCEP/ATPIII criteria; given the focus put on insulin resistance, individuals applicable to this definition may be particularly prone to develop diabetes mellitus; a diabetologist definition of the syndrome. Finally, the more recent International Diabetes Federation (IDF) consensus [8] puts the focus on abdominal/visceral obesity.......