What determines weight gain, loss, or maintenance?

Weight gain, loss, or maintenance is fundamentally determined by caloric balance, which refers to the relationship between the number of calories consumed through food and beverages and the number of calories expended through metabolic processes and physical activity.

When caloric intake exceeds caloric expenditure, the body stores the excess energy as fat, leading to weight gain. Conversely, when caloric expenditure exceeds caloric intake, the body utilizes stored fat for energy, resulting in weight loss. For weight maintenance, caloric intake and expenditure must remain in equilibrium, meaning that the number of calories consumed equals the number of calories burned.

While other factors like exercise type, hydration levels, and body composition play important roles in overall health and fitness, they do not directly dictate weight change in the same way that caloric balance does. Exercise can influence caloric expenditure and body composition, hydration can affect weight temporarily due to fluctuations in water retention, and body composition provides insights into the proportion of muscle and fat, but these factors operate within the framework of caloric balance.