Your body needs energy to function, and it gets this energy from food. The fuel you burn in order to keep your body running is measured in calories, and different foods have varying calorific values. The speed at which your body burns calories is known as your metabolic rate. Everyone’s body functions differently, and some people can burn calories at a much faster rate than others.
Your body burns energy at different rates depending on your activity. When you’re at rest, your calorie burning rate is known as your Resting Metabolic Rate (RMR). This is the fuel your body burns simply to keep your internal bodily systems functioning – your respiratory system for example. Nearly three quarters of the calories you burn in a day are used up in this way.
The act of eating itself also burns up fuel – this is known as the Thermic Effect of Feeding (TEF), and explains why eating even cold foods makes you feel warmer. Absorbing and digesting food creates a lot of work for the body, including triggering digestive enzymes and increasing blood flow around the body. TEF accounts for another 10% of the calories you burn in a day.
The third way the body uses calories is by physical activity, which burns between 15 and 30% of your daily usage. Physical activity doesn’t only mean sport or fitness regimes, it also includes even ‘casual’ movement, such as fidgeting or shivering. But when you engage in more rigorous activity, such as sport or training, your body will burn up extra fuel to power its self. Exercise also increases your body’s metabolic rate for between 6 and 36 hours afterwards, and helps you to burn more calories even when at rest.