1.1 Introduction: Obesity, Metabolic Syndrome, and Type 2 Diabetes Epidemics: The Role of Nutrition
Over the last 50 years, people have experienced drastic changes in their living environment, behavior, and lifestyle. These changes have led to an alarming increase in the incidence of type 2 diabetes, overweight, and frank obesity [1]. The replacement of human labor with automation, increased consumption of âempty calories,â globalization of technology, and improvement in transportation are some of the factors that have led to this sad state of affairs [2]. A study on the prevalence of obesity, carried out by the World Health Organization (WHO) and the International Obesity Task Force, found that the worldwide prevalence of overweight individuals, after adjusting for ethnic differences, was 1700 million, of which 312 million were obese [1, 3]. Data from successive cohorts of the National Health and Nutrition Examination Survey [4] show that the average waist circumference of adults in the USA increased progressively from 95.5 cm in 1999â2000 to 98.5 cm in 2011â2012. The same study reported that prevalence of abdominal obesity increased significantly from 46.4% in 1999â2000 to 54.2% in the same period of observation. Of note, over the past 20 years, prevalence rates for obesity have tripled in those developing countries that have adopted western lifestyles [1], including reduced physical activity and overconsumption of highâcalorie meals. Accordingly, obesity is now considered one of the greatest health threats in the world, for it is the major risk factor of a wide range of noncommunicable disease and, particularly, type 2 diabetes [1, 3].
Today, the extent of the type 2 diabetes epidemic is growing worldwide, in both developed and emerging countries. WHO reports that the number of people with diabetes has almost quadrupled in a quarter of a century, from 108 million in 1980 to 422 million in 2014, that is, from 4.7% to 8.5% of the general population. Prevalence of diabetes has risen even more rapidly in middleâ and lowâincome countries (http://www.who.int/mediacentre/factsheets/fs312/en), an alarming trend that represents a major burden for public health systems worldwide. WHO estimated that 1.6 million deaths worldwide were directly linked to diabetes in 2015 (http://www.who.int/mediacentre/factsheets/fs312/en). The control of diabetes, a major risk factor for vascular diseases, is crucial for the prevention of debilitating and lifeâthreatening conditions such as kidney failure, blindness, stroke, heart attacks, and lower limb complications [5]. Vascular complications are among the most serious manifestations of type 2 diabetes. Atherosclerosis is the main factor limiting life expectancy; retinopathy and diabetic nephropathy (DN) cause blindness and endâstage renal disease [5]. The most efficacious approach to prevent vascular complications of diabetes includes strict blood glucose control with antidiabetic drugs and/or insulin, antihypertensive treatment, and statin administration to decrease cholesterol levels. Despite current therapeutic advances, diabetes complications are a persistent concern because keeping blood glucose in check, which is effective to delay the onset of nephropathy and retinopathy, is less effective at reducing diabetesâassociated cardiovascular disease [6]. Therefore, identification of novel therapeutic approaches for diabetes, obesity, metabolic syndrome, and their vascular complications is an enthusiastic area of research.
Lifestyle adjustment is a key point for treatment of type 2 diabetes, metabolic syndrome, and obesity [7], which result from a predisposing genetic background exacerbated by an unhealthy lifestyle, namely sedentary behavior and poor diet quality. The crucial step is weight loss, which is associated with numerous beneficial effects, including lipid profile improvement, reduction of glucose and inflammation marker levels, and normalization of blood pressure and left ventricular mass. The combined longâterm gain of these changes is abatement of the diabetesâassociated death risk and, in obese subjects and in patients with metabolic syndrome, delayed progression to type 2 diabetes [8, 9]. Both exercise and diet correction contribute to reduction and maintenance of body weight [10], which is associated with improvement of all manifestations of metabolic syndrome and reduction of incidence of vascular complications [11]. In particular, diet interventions can help prevent the onset and progression of cardiometabolic disorders and DN [12].
The diet composition can also affect vascular health through the protective effects provided by specific food components. Besides wellâestablished general recommendations, such as restricting intake of fat of animal origin; increasing servings of fruits, vegetables, and fiberârich cereals; avoiding industrially processed foods; and increasing the protein fraction of white meat and fish, a major area of discussion today is supplementing the diet with functional foods. These sources provide nutraceuticals with antiglycemic, antiâinflammatory, antioxidant, and additional protective effects for metabolic disorders and diabetic vascular complications [13]. Our chapter deals with the vast literature that has appeared in the last decade on specific food nutrients with purported beneficial effects to prevent diabetes and its microvascular and macrovascular complications, including nephropathy, retinopathy, ischemic heart disease, and cerebrovascular disease.
