The Transition From Undernutrition to Overnutrition Under Adverse Environments and Poverty: The Risk for Chronic Diseases

Abstract

Nutritional transition is an important public health issue in developing countries, where switch from undernutrition to overnutrition/obesity is rapidly occurring, often within two or three generations. Such transition is related to changes in lifestyle, with people having more access to western high-caloric diets. In developing countries, settings of poverty, poor sanitation and hygiene are still common, where children are exposed to numerous enteric pathogens, pollutants, and other biohazards. Populations living under such adverse environments and facing the nutritional transition may have increased risks for chronic illnesses in later life, including diabetes, cardiovascular, and neurodegenerative diseases. This opinion paper summarizes novel findings and recent literature addressing the nutrition transition under adverse environments, including the gut microbiota-brain axis dysfunction and their lasting effects with deleterious consequences for later development. According to the World Health Organization (WHO), approximately 462 million adults are underweight, 1.9 billion are overweight or obese, and 2 billion are micronutrient deficient (1). In addition, 38 million children below 5 years of age were overweight or obese in 2019 and more than 340 million children and adolescents (5 to 19 years) were overweight or obese in 2016 (2). Obesity associated with micronutrient deficiency has great repercussions in childhood and deserves special attention in middle and low income countries (3), which may be even more aggravated by poverty and unbalanced diets. In developing countries, lifestyle changes amidst the disarray of urbanization, increasing poverty (with proliferating shantytowns, poor sanitation, and hygiene), crowding, and altered dietary habits. Continuous exposure to harmful pollutants (mercury, lead, arsenic, asbestos etc.) and environmental pathogens may accumulate and lead to a detrimental exposome throughout life with long-term health consequences (4). In developing countries with emerging economies, a double burden of malnutrition (DBM) often occurs even in impoverished areas. The DBM is defined by WHO as “the coexistence of undernutrition along with overweight, obesity or diet-related non-communicable diseases (NCD), within individuals, households and populations, and across the life-course” and may be aggravated by poor environmental circumstances and genetic predispositions (1). Although a large proportion of deaths among children under five are attributed to malnutrition, overweight and obesity in this age group and older are on the rise (5). The increased risk of NCD related with the nutritional transition in developing countries is a public health concern, due to the potential economic impact and oversaturation of the health system infrastructure (6). Furthermore, when nutritional deprivation or infection occurs early in life, such as in the prenatal phase and/or up to 3 years of age, the individual undergoes metabolic changes that can lead to greater susceptibility to developing obesity as an adult (7). DBM can cause long-term effects, especially when their components develop early, and each of them can increase the chances of the other occurring (8). The transition to hypercaloric diets is a global health concern. Hypercaloric intake is characterized by high-carbohydrate and fat consumption, both leading to obesity. Studies have shown that maternal obesity during pregnancy can lead to overweight and other metabolic effects in the offspring through epigenetic mechanisms, such as DNA methylation (9). The coexistence of these opposing nutritional patterns reflects, in part, social and economic inequalities. Other factors such as the increased life expectancy also contribute, as elderly populations are more vulnerable to malnutrition given their psychological, social and health-related risks and chronic diseases (10). Several studies point to the effects of fetal programming and maternal and environmental factors during early life on the development of diseases in adulthood (11–16). Maternal nutrition even before pregnancy can affect the development of the fetus with later risk for cardiovascular/metabolic diseases (12). Early undernutrition followed by later overweight increases the risk of NCD, imposing a high metabolic load on a reduced or altered capacity for homeostasis. In women, early childhood undernutrition increases the risk of complications in childbirth later in life (13). In countries with poor sanitary conditions, the occurrence of the APOE4, a recognized gene associated with increased risk for acquiring Alzheimer's disease, may favor maternal fertility and promote protection against childhood diarrhea, while possibly increasing the risk of NCD with aging (14). In animal models, maternal obesity affects leptin mRNA expression and its peak in offspring (15). Hyperleptinemia leads to leptin resistance in neonates, favoring hyperphagia and can permanently affect the regulation of appetite (16). These trajectories throughout life are shaped both by driving factors of society–that is, rapid changes in diets, dietary norms and patterns of physical activity–and by broader ecological factors, such as pathogen exposure (8). In the example of Brazil, the most recent National Health Survey (17) pointed out that 60.3% of the population over 18 years old is overweight, while underweight reaches 1.6% of the inhabitants over 25 years old. A systematic review (18) pointed out that the prevalence of underweight was approximately 10% in children from different regions of the country, reaching 21% due to social disparities. The prevalence of overweight was also approximately 10%, with a reduction to 6% in populations with social inequality. The increase in the body mass index (BMI) in the population has grown significantly not only in Brazil but in other low- and middle-income countries around the globe, justifying the increase in the...