During the International Congress on Obesity (ICO) 2026, organized by the World Obesity Federation and held in Mexico City, Mexico, speakers highlighted a crucial point about the origins of childhood obesity: The condition reflects a complex web of interrelated factors, including genetic variations, parental weight, socioeconomic status, and place of residence, all of which influence risk. Addressing these factors could therefore help support earlier interventions aimed at preventing comorbidities in adulthood.

Antje Körner, MD, pediatrician scientist and professor of metabolic research at University of Leipzig in Leipzig, Germany, explained that childhood obesity develops through the interaction of multiple factors, including biological makeup, genetic inheritance, and weight-regulating mechanisms, as well as the environmental and social conditions to which children are exposed from an early age.

She emphasized that throughout childhood, these factors can accumulate and contribute to weight gain, the onset of insulin resistance, hypertension, and cardiovascular disorders at increasingly younger ages.

“We could say that it’s all due to genetics or just nutrition, but these factors act together: our biological makeup, mechanisms that determine body weight, and our epigenetic and environmental context,” she explained.

She noted that childhood obesity should be managed by a multidisciplinary team involving several specialties, including cardiology, because it cannot be addressed solely through pediatrics. She also emphasized the importance of assessing each patient’s individual condition, including possible genetic abnormalities, with the goal of providing the best treatment and preventing comorbidities such as hypertension and diabetes.

Identifying Genetic Abnormalities

Körner said that identifying genetic alterations early in childhood and adolescence may help prevent the development of severe obesity and related comorbidities. She noted that her research group found that ectopic expression of the ASIP gene (agouti signaling protein) interferes with the melanocortin 4 receptor, which is involved in regulating food intake and energy expenditure.

Under normal conditions, this gene is expressed in the skin and helps determine skin and hair color. However, when it is expressed ectopically, it can affect regulation of food intake.

She said this finding emerged after her group obtained an adipose tissue sample from a 12-year-old girl with severe obesity and insulin resistance for whom standard genetic analyses had failed to explain the condition. After the adipose tissue sample was obtained, transcriptomic analyses were performed, and the ASIP gene stood out.

These transcriptomic analyses of adipose tissue were then replicated in a sample of 8000 children and adults with and without obesity, in whom 26 carriers of this ectopic ASIP expression were identified. The results of this research were published in Nature in 2022.

“The finding has several implications. First, it expands our understanding of the pathogenesis of human obesity. Furthermore, it requires a reevaluation of diagnostic algorithms so that they can detect chromosomal duplications and rearrangements, not just point variants,” she noted.

Parental Weight: A Major Risk Factor

Körner noted that one of the main risk factors for childhood obesity is parental overweight or obesity, especially maternal obesity.

She said this association is not explained solely by shared dietary habits within the family. Metabolic and epigenetic factors that can be transmitted even before birth also appear to play a role.

The specialist explained that when a mother is overweight, the likelihood that her child will develop obesity is high. “If a behavioral or environmental factor — such as prolonged screen time — is added to this predisposition, the risk increases exponentially.”

She also noted that paternal weight matters because overweight in the father is associated with a greater likelihood that the child will develop obesity and insulin resistance.

She pointed out that experimental research has identified a possible molecular pathway for this transmission. “Through an epigenetic mechanism, transfer RNA fragments present in sperm can transmit metabolic information to offspring. Therefore, both mothers and fathers are important.”

In addition to parental weight, other biological factors associated with childhood obesity include weight gain during pregnancy and birth weight. Körner cautioned that these variables must be analyzed together with socioeconomic, behavioral, and environmental conditions.

Fetal Growth and Obesity Risk

Nutrition during pregnancy is another factor linked to the risk for childhood obesity. A study led by Guadalupe López Rodríguez, PhD, professor of nutrition and food science at the Autonomous University of the State of Hidalgo in Pachuca de Soto, Mexico, estimated that excessive fetal growth could contribute to approximately 4% of future cases of childhood obesity and 5% of future cases of obesity in adulthood in Mexico.

The study, presented at ICO 2026, aimed to quantify the frequency of large-for-gestational-age births and macrosomia in Mexico during 2023 and 2024, as well as to estimate their potential contribution to the country’s future obesity burden.

The study analyzed 2,780,125 live birth records (1,439,626 in 2023 and 1,340,499 in 2024) from Mexico’s National Health Information System. Any newborn with a weight above the 90th percentile for gestational age and sex, according to the INTERGROWTH-21st international standards, was considered large for gestational age. Macrosomia was defined as a birth weight of 4000 g or more.

To estimate the potential impact of excessive fetal growth on the future burden of obesity, the research team combined the observed frequency of exposure (large for gestational age or macrosomia) in the national cohort with estimates from international meta-analyses and national obesity prevalence rates in Mexico (18.1% among children and 37.1% among adults, according to ENSANUT 2022, Mexico’s National Health and Nutrition Survey), in order to project the number of cases that could occur in this birth cohort.

Among the 2.78 million live births analyzed, 51.6% were male, and the average gestational age was 38.5 weeks. Large for gestational age was the most common manifestation of neonatal excess weight, identified in 232,730 newborns (8.37%). Of these, 175,333 (6.31%) had only large-for-gestational-age status, and 57,397 (2.06%) had both large-for-gestational-age status and macrosomia.

Isolated macrosomia was rare and was documented in 2146 newborns (0.08%). Overall, 8.45% of Mexican newborns exhibited excessive fetal growth.

The estimated population-attributable risk was 4.05% for childhood obesity and 5.28% for adult obesity. Based on these results, the study projects that approximately 20,379 future cases of childhood obesity and 54,439 future cases of adult obesity could occur in this national birth cohort as a result of excessive fetal growth.

“The results highlight the importance of strengthening nutritional care strategies during pregnancy and incorporating fetal and neonatal growth monitoring into national health surveillance systems, with the goal of promoting better metabolic health from the earliest stages of life,” the research team noted.

Excessive fetal growth, defined as large for gestational age or macrosomia, reflects a state of overnutrition during intrauterine life and has been consistently associated with metabolic abnormalities that can persist throughout life.

Food Environment as a Determinant Risk

Körner also emphasized that socioeconomic status has been identified as one of the most important risk factors for childhood obesity because fast-food outlets tend to predominate in areas with greater economic deprivation, whereas neighborhoods with more resources generally have a more diverse food supply.

“These conditions determine the foods that families can access immediately and limit their ability to choose different options, regardless of individual knowledge or intentions,” she added.

She also noted that differences between urban and rural areas affect the risk for childhood obesity, because in cities, lack of green space may lead children to spend more time in front of screens and reduce opportunities for outdoor play.

She emphasized that strategies to combat obesity must include urban, social, and dietary changes rather than being limited to individual lifestyle recommendations.

During ICO 2026, Alejandra Contreras Manzano, PhD, population nutrition researcher at Mexico’s National Institute of Public Health in Cuernavaca, Mexico, highlighted the importance of regulating sales of ultraprocessed foods to help prevent childhood obesity.

She added that the institute is assessing how schools are implementing guidelines governing the sale of foods and beverages, as well as rules related to products carrying front-of-package warning labels. To do so, researchers are analyzing a sample of 350 elementary schools, evaluating factors such as the nutritional composition of foods and beverages available on school grounds.

In addition, they are analyzing biochemical indicators, health status, and eating habits among girls and boys to better understand the school environment and its relationship to nutrition. So far, the analysis has found greater availability of vegetables and healthy foods in schools located in rural areas.

Mexico’s ENSANUT survey (2020-2023) shows that overweight and obesity affect 36.5% of school children aged 5-11 years and 40.4% of adolescents aged 12-19 years in the country.

The experts declared having no relevant financial relationships.

This story was translated from Medscape’s Spanish edition.