Childhood obesity develops through a complex web of genetic, biological, and environmental factors that work together, not in isolation. New research presented at the International Congress on Obesity 2026 reveals that addressing these interconnected causes, rather than focusing solely on nutrition or exercise, could help prevent serious health complications in adulthood.

What Causes Childhood Obesity Beyond Just Food Choices?

For decades, childhood obesity has been framed as a simple equation: too many calories in, not enough calories burned. But experts now understand the reality is far more nuanced. Childhood obesity reflects the interaction of multiple factors including biological makeup, genetic inheritance, weight-regulating mechanisms, and the environmental and social conditions children face from early childhood.

"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," explained Antje Körner, a pediatrician scientist and professor of metabolic research at the University of Leipzig in Germany.

Antje Körner, MD, Professor of Metabolic Research, University of Leipzig

Throughout childhood, these factors accumulate and contribute to weight gain, insulin resistance, high blood pressure, and cardiovascular disorders at increasingly younger ages. This is why Körner emphasizes that childhood obesity cannot be addressed through pediatrics alone; it requires a multidisciplinary team involving cardiology and other specialties.

How Do Genes Influence a Child's Weight?

Genetic research has uncovered surprising mechanisms that affect how children's bodies regulate food intake and energy use. Körner's research group discovered that ectopic expression of the ASIP gene (agouti signaling protein) interferes with the melanocortin 4 receptor, which plays a key role in regulating appetite and energy expenditure. Normally, this gene is expressed only in the skin and helps determine skin and hair color. However, when expressed in the wrong location, it can disrupt food intake regulation.

This discovery emerged after researchers obtained an adipose tissue sample from a 12-year-old girl with severe obesity and insulin resistance whose condition couldn't be explained by standard genetic tests. After performing transcriptomic analyses (which examine which genes are active in tissue), the ASIP gene stood out as the culprit. When researchers replicated these analyses in a sample of 8,000 children and adults with and without obesity, they identified 26 carriers of this ectopic ASIP expression. The findings were published in Nature in 2022.

Körner noted that identifying genetic alterations early in childhood and adolescence may help prevent the development of severe obesity and related complications. The discovery also requires a reevaluation of diagnostic approaches to detect chromosomal duplications and rearrangements, not just point mutations.

What Role Does Parental Weight Play?

One of the strongest risk factors for childhood obesity is parental overweight or obesity, particularly maternal obesity. Importantly, 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 significant role.

When a mother is overweight, the likelihood that her child will develop obesity is high. If behavioral or environmental factors, such as prolonged screen time, are added to this genetic predisposition, the risk increases exponentially. Paternal weight also matters; overweight in the father is associated with a greater likelihood that the child will develop obesity and insulin resistance.

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. This means both mothers and fathers play important roles in shaping their children's metabolic health.

How Can Nutrition During Pregnancy Affect a Child's Future Weight?

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

The study analyzed 2,780,125 live birth records from 2023 and 2024 in Mexico. Researchers defined large-for-gestational-age births as newborns weighing above the 90th percentile for their gestational age and sex, and macrosomia as a birth weight of 4,000 grams or more. Among the 2.78 million births analyzed, 8.45% of Mexican newborns exhibited excessive fetal growth. Of these, 8.37% were classified as large-for-gestational-age, and 0.08% had isolated macrosomia.

Based on these findings, the research team projected 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. Excessive fetal growth reflects a state of overnutrition during intrauterine life and has been consistently associated with metabolic abnormalities that can persist throughout life.

Steps to Support Healthier Weight Development in Children

• Assess Individual Genetic Risk: Work with pediatricians to identify possible genetic abnormalities early in childhood and adolescence, which may help prevent severe obesity and related complications like hypertension and diabetes.
• Strengthen Prenatal Nutrition: Ensure adequate but not excessive nutrition during pregnancy to prevent excessive fetal growth, which can program metabolic problems that persist into childhood and adulthood.
• Adopt a Multidisciplinary Approach: Involve multiple medical specialties, including cardiology, pediatrics, and nutrition, rather than relying on a single approach, since childhood obesity involves complex biological, genetic, and environmental factors.
• Monitor Parental Weight: Recognize that parental weight status, particularly maternal weight, significantly influences a child's obesity risk through both genetic and epigenetic mechanisms that can be transmitted before birth.
• Incorporate Fetal and Neonatal Growth Monitoring: Include fetal and neonatal growth monitoring into national health surveillance systems to promote better metabolic health from the earliest stages of life.

Why Does Socioeconomic Status Matter for Childhood Obesity?

Beyond genetics and prenatal factors, socioeconomic status has been identified as one of the most important risk factors for childhood obesity. This reflects the reality that access to nutritious food, safe spaces for physical activity, and quality healthcare varies significantly based on income and neighborhood. Körner emphasized that childhood obesity should be managed by considering each patient's individual condition, including their socioeconomic circumstances, with the goal of providing the best treatment and preventing comorbidities.

The research presented at the International Congress on Obesity 2026 underscores a critical shift in how experts understand and approach childhood obesity. Rather than viewing it as a simple behavioral problem, the evidence shows it results from a complex interplay of factors that begin before birth and continue throughout childhood. By identifying genetic risk factors early, supporting optimal prenatal nutrition, and addressing socioeconomic barriers to healthy living, healthcare providers may be able to intervene more effectively and prevent the cascade of metabolic complications that often follow childhood obesity into adulthood.