Energy balance

Energy balance is the difference between the calories you take in from food and drink and the calories you expend. A negative balance (a deficit) leads to weight loss; a positive balance (a surplus) to weight gain; and matching the two maintains weight.

It matters because it is the fundamental principle governing body-weight change. Diet composition, food quality and hormones influence hunger, adherence and body composition, but they operate within this energy-balance framework.

In practice, you create the balance you want by estimating your TDEE and setting intake above or below it for your goal.