How does consuming more calories than the body uses lead to obesity?

Obesity is defined as the excessive accumulation of body fat, which typically occurs when an individual consumes more calories than their body utilizes for energy.1

When caloric intake consistently exceeds energy expenditure, the body stores the surplus energy as fat within adipose tissue. This tissue, composed of specialized cells called adipocytes, serves as the body's primary energy reservoir. While the body is designed to store and mobilize these fat stores as needed, a chronic imbalance—often driven by the combination of high-calorie diets and sedentary lifestyles—leads to the progressive buildup of this tissue, resulting in obesity.1234

Weight management is fundamentally determined by the ratio of energy consumed to energy expended over time. When this balance is disrupted by overeating and a lack of physical activity, the body’s natural regulatory mechanisms, such as the hormone leptin, may be overwhelmed or become ineffective, further contributing to the condition.43