It is said that you can’t outrun a bad diet. Food accounts for 100% of the calories we consume. By contrast, deliberate exercise only accounts for about 10-30% of the energy the body uses. Energy expenditure has three main components:
- Basal Metabolic Rate : 60-80% of expenditure is used for the basic functioning of the body at rest (breathing, thinking, digesting, etc.)
- Digestion : 10% of the energy expended is for breaking down food, which is called the thermic effect of food
- Physical Activity: 10-30% of energy expenditure is from physical activity
You may be better off trying to lose weight by thinking hard, as our brains are responsible for 25% of our energy expenditure despite accounting for only 2% of our body weight.
These images show the components of the metabolism and the theory that there is a constrained amount of energy that can be used up by physical exercise: