**1. Introduction**

Obesity and chronic noncommunicable diseases, such as diabetes and cardiovascular disease, lead to the main causes of disability and premature mortality worldwide. In recent decades, the prevalence of obesity in the world has increased exponentially in children and adolescents, going from 0.7% to 5.6% in boys and from 0.9% to 7.8% in girls, between 1975 and 2016 [1]. Simultaneously, the incidence of type 2 diabetes (T2D) in the youth increased from 9 to 12.5 cases per 100,000 between 2003 and 2012 [2]. Additionally to the increase in obesity and diabetes, the development of unhealthy habits, such as inadequate diet and sedentary lifestyle in young people, have contributed to the development of cardiovascular diseases (CVD) at an early age [3]. Data from the National Health and Nutrition Examination Survey (NHANES) estimated a prevalence of ischemic heart disease of 0.5–0.6% in the United States for the period 2011–2014 in young adults between 20 and 39 years old. This trend is increasing, and it is expected that by 2030, 43.9% of the US adult population will have some type of cardiovascular disease [4].

The attempts to prevent or palliate the current wave of obesity and the following noncommunicable diseases should be funded at the beginning of human life. An interesting hypothesis is proposed: The Developmental Origins of Health and Disease (DOHaD) that is derived from the Barker hypothesis, which proposed that nutrition during the intrauterine period and exposure to infections after birth determine susceptibility to disease and death from coronary artery disease. This hypothesis has evolved, and currently, critical periods have been identified in fetal life and early childhood, which will determine growth, metabolism, neurogenesis, and future disease risk, expanding the hypothesis to other disorders, such as obesity, diabetes, cardiovascular disease, allergies, and neurological alterations, throughout the life. The DOHaD concept is based on epigenetics and explains the possibility of variations in the programming of the fetus and the infant through the modification of environmental factors, such as diet and infections, in these window periods [5].

Another main component involved in the early life stages is the gut microbiota, defined as the microbial ecosystem that colonizes the gastrointestinal tract, depending on perinatal and environmental factors, such as diet. Its balance is associated with health and its imbalance with the presence of various diseases, although the mechanisms involved have not been fully elucidated; and as with the DOHaD theory, window periods have been identified where its modulation is possible, especially in the perinatal period and up to preschool age [5, 6]. Thus, the aim of this chapter is to discuss the role of the perinatal maternal and infant diet and the gut microbiota to explain the development of chronic noncommunicable diseases from the DOHaD perspective, as key factors in the modulation of epigenetic programming mechanisms, to identify the areas of opportunity for preventive purposes in early childhood.
