Overweight and obesity are among the fastest-growing public health problems of modern times and simultaneously one of the greatest silent killers of the 21st century. If current trends do not change, by 2050 approximately 60% of adults (3.8 billion people) and nearly one-third of children (746 million) will live with this condition - more than twice as many as in 1990 [1].

Obesity does not arise from a single cause. It involves a complex interplay of biological mechanisms, including genetic susceptibility and hormonal regulation, along with factors such as dietary patterns, physical inactivity, family environment, sleep disorders, and stress, which together promote excessive energy intake and insufficient energy expenditure.

Therefore, today we understand obesity as a multifactorial disease in which genetics and physiology influence susceptibility, while the environment decisively determines how this susceptibility is expressed in practice [2].

How do we define overweight and obesity?

Nutritional status is most commonly assessed using Body Mass Index (BMI), which represents a basic screening tool in clinical practice and research. It is calculated as the ratio between body weight (in kilograms) and the square of height (in meters).

In children and adolescents up to 19 years of age, BMI is always interpreted according to age and sex, as the body changes rapidly during the growth period. Values are therefore compared with growth charts that enable assessment of nutritional status relative to peers. Overweight is defined as values between the 85th and 95th percentiles, while obesity is defined as values above the 95th percentile [2].

In adults, interpretation is simpler: overweight is defined as BMI ≥ 25 kg/m², and obesity as BMI ≥ 30 kg/m² [1]. However, it should be noted that BMI is a useful screening tool but does not provide information about body composition or fat distribution. Therefore, in individual cases, such as in highly muscular individuals, it may overestimate the degree of nutritional status.

When defining both of these risk conditions, it is important to determine where in the body fat accumulates. Particularly risky is the accumulation of fat in the abdominal area, known as central or visceral obesity, where fat deposits around internal organs. Such adipose tissue is metabolically active and associated with increased risk of insulin resistance, type 2 diabetes, elevated blood lipids, and cardiovascular disease. Research shows that indicators of central obesity predict metabolic risk more reliably than BMI alone [3].

In practice, central obesity is often assessed using the waist-to-height ratio (WHtR). It is calculated by dividing waist circumference (in centimeters) by height (in centimeters). Values above 0.5 indicate increased risk, which can be simply interpreted as: waist circumference should be less than half of height [4].

Why overweight and obesity pose health risks

Excess adipose tissue is not just a passive energy reserve, but metabolically active tissue that triggers chronic low-grade inflammation in the body. This does not cause noticeable symptoms but long-term burdens metabolism and the vascular system.

This condition gradually leads to insulin resistance, disturbances in blood sugar regulation and fat metabolism, and disrupts the hormonal balance that regulates appetite, satiety, and energy expenditure. Visceral adipose tissue, which surrounds internal organs, is particularly problematic as it is metabolically more active and associated with greater risk of chronic diseases.

In children and adolescents, overweight already increases the likelihood of type 2 diabetes, dyslipidemia, hypertension, musculoskeletal problems, and psychosocial difficulties such as depression, anxiety, and lower quality of life [2].

In adults, overweight increases the risk of cardiovascular diseases and type 2 diabetes, while obesity additionally contributes to certain types of cancer and significantly shortens healthy life expectancy. Global analyses show that high BMI contributes to several million deaths annually, primarily from cardiovascular diseases [3].

Key factors influencing body weight

The following briefly presents the closely intertwined key factors that contribute to the development of overweight and obesity.

- Genetic susceptibility

Genetic factors influence appetite, metabolism, and the way energy is stored, making some individuals more susceptible to developing overweight. However, genetics alone does not cause obesity. It develops primarily in an environment that promotes high energy intake and low energy expenditure, the so-called obesogenic environment, which is often difficult to avoid in modern lifestyles [5].

This means that genetic susceptibility may increase risk, but obesity most commonly develops only when this susceptibility meets inappropriate dietary habits.

- Hormonal dysregulation: ghrelin and leptin

Two main hormones regulate appetite and energy balance: ghrelin (hunger hormone) and leptin (satiety hormone). In normal body function, ghrelin rises before a meal and stimulates hunger, then decreases after eating, while leptin signals sufficient energy reserves and contributes to feelings of satiety. With prolonged energy surplus, appetite regulation is disrupted. Leptin resistance develops, where the satiety signal no longer works effectively, while ghrelin regulation is also disrupted. The result is increased hunger, greater energy intake, and persistence of overweight and obesity [2].

- Dietary patterns

Dietary patterns significantly influence the amount of energy consumed.

Modern diets often rely on energy-dense and highly processed foods that contain more fat, sugar, and salt and are therefore highly palatable. At the same time, such foods are readily available and easy to use, so we reach for them more frequently in fast-paced lifestyles. Research shows that individuals consuming such food intake more energy than when eating minimally processed foods, as pronounced flavors encourage greater intake [6].

- Physical inactivity

Low levels of physical activity reduce energy expenditure and accelerate the imbalance between energy intake and expenditure. Modern lifestyles, which include much sitting and too little movement, significantly increase the risk of developing overweight and obesity, which scientific research has confirmed for many years [7].

- Sleep disturbances

Lack of sleep affects the regulation of hunger and satiety hormones and is associated with greater energy intake. With sleep deprivation, ghrelin (hunger hormone) secretion increases and leptin (satiety hormone) function decreases, while the desire for energy-rich food increases. Research shows that shorter sleep duration increases the risk of developing overweight and obesity in children and adults [8].

- Stress

Chronic stress affects hormonal balance and can promote overeating, especially reaching for energy-dense food. With prolonged stress, cortisol secretion increases, which is associated with greater appetite and more pronounced cravings for sweet and fatty foods. At the same time, cortisol also affects metabolism by promoting fat storage, especially in the abdominal area, which can contribute to weight gain [9].

- Family environment

Dietary and behavioral habits are formed in early childhood. A family environment that does not support regular meals, physical activity, and sleep increases the risk of developing overweight and obesity. Parental role models, food availability, and daily habits such as meal times, shared meals, and screen time also play an important role, as these factors significantly influence the formation of long-term habits [10].

Conclusion

Obesity often develops gradually, from childhood through adolescence to adulthood. Therefore, early recognition of risky habits and timely intervention are crucial for long-term health.

For effective maintenance of healthy body weight, regular monitoring of body weight (e.g., once weekly) is beneficial for adults. In children and adolescents, body weight is always assessed in the context of growth and development, so monitoring takes place primarily during regular systematic examinations with a pediatrician or school physician.

Would you like practical support?

At the HFL Institute, we are happy to help you develop balanced habits in your daily life and environment.

References

  1. Phelps, N.H., et al., Worldwide trends in underweight and obesity from 1990 to 2022: a pooled analysis of 3663 population-representative studies with 222 million children, adolescents, and adults. The Lancet, 2024. 403(10431): p. 1027-1050.
  2. Jebeile, H., et al., Obesity in children and adolescents: epidemiology, causes, assessment, and management. The Lancet Diabetes & Endocrinology, 2022. 10(5): p. 351-365.
  3. Neeland, I.J., P. Poirier, and J.P. Després, Cardiovascular and Metabolic Heterogeneity of Obesity: Clinical Challenges and Implications for Management. Circulation, 2018. 137(13): p. 1391-1406.
  4. Eslami, M., et al., Optimal cut-off value of waist circumference-to-height ratio to predict central obesity in children and adolescents: A systematic review and meta-analysis of diagnostic studies. Front. Nutr., 2023. Volume 9 - 2022.
  5. Loos, R.J.F. and G.S.H. Yeo, The genetics of obesity: from discovery to biology. Nature Reviews Genetics, 2022. 23(2): p. 120-133.
  6. Hall, K.D., et al., Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of <em>Ad Libitum</em> Food Intake. Cell Metabolism, 2019. 30(1): p. 67-77.e3.
  7. Silveira, E.A., et al., Sedentary behavior, physical inactivity, abdominal obesity and obesity in adults and older adults: A systematic review and meta-analysis. Clinical Nutrition ESPEN, 2022. 50: p. 63-73.
  8. Chaput, J.-P., et al., The role of insufficient sleep and circadian misalignment in obesity. Nature Reviews Endocrinology, 2023. 19(2): p. 82-97.
  9. Tomiyama, A.J., Stress and Obesity. Annu Rev Psychol, 2019. 70: p. 703-718.
  10. Scaglioni, S., et al., Factors Influencing Children's Eating Behaviours. Nutrients, 2018. 10(6).