Do we know what happens inside the body during weight gain and obesity?

Obesity is commonly viewed as the accumulation of excess fat in subcutaneous tissues. However, this visible fat is only what can be seen with the naked eye. The fat accumulated in these tissues is not merely stored; it exerts hormonal and metabolic effects on the body. In fact, adipose tissue functions as an organ, contributing to the worsening of the obesity problem as fat stores increase beyond certain levels.

In addition to the impact of obesity on the adipose system, other major body systems are also affected. Notable changes are observed in the skin (integumentary system), including slower wound healing, an increased risk of acne, and higher rates of sweating. Obesity often leads to significant changes in the endocrine system, with increased insulin production, elevated levels of the hormones leptin and ghrelin, and higher stress hormones, among many others. Furthermore, obesity increases the risk of muscle atrophy and osteoporosis, and impairs fatty acid metabolism in skeletal muscles. These negative effects are not limited to these organ systems but also extend to the nervous system (central and peripheral), the cardiovascular system (heart and blood vessels), the respiratory system, the digestive system, the reproductive system, and the urinary system.

It has been proven that obesity affects both the central and peripheral nervous systems. Although they are different, both appear to be susceptible to functional impairments caused by obesity, suggesting common mechanisms contributing to obesity-related diseases that affect both systems.

Obesity also alters many distinct aspects of the central nervous system. Significant structural changes occur in the brain; these structural changes have been linked to alterations in brain function among individuals with obesity, suggesting that these changes may also influence behavior (Raji et al., 2010). Specific psychological and behavioral changes also appear to stem from the effects of obesity on the central nervous system, including: changes in eating behaviors and feelings of satiety, alterations in reward mechanisms, decreased attention and learning, increased memory deficits, and a higher risk of neurocognitive decline, with a simultaneous rise in the risk of developing dementia and Alzheimer's disease.