Calories are burned in humans through three main processes:

1. Basal Metabolic Rate (BMR) – This is the energy your body uses at rest to maintain essential functions like breathing, circulation, and cell production. BMR accounts for about 60-75% of total calorie expenditure.
2. Physical Activity – Any movement, from walking to intense exercise, burns calories. This includes both structured exercise (like running or weightlifting) and non-exercise activity thermogenesis (NEAT), which includes things like fidgeting or walking around the house.
3. Thermic Effect of Food (TEF) – Digesting, absorbing, and metabolizing food requires energy. TEF accounts for about 10% of total calorie expenditure, with protein requiring the most energy to digest compared to carbs and fats.

Other factors affecting calorie burn include age, muscle mass, genetics, hormones, and overall health.