We talked about how the food you consume is your calorie intake. But I'm sure you're wondering... How do you burn calories? There are 3 ways:
1) RMR (Resting Metabolic Rate) is the main contributor to our daily calorie burning. It is defined as the calories your body burns at rest while functioning at a base level. This includes the energy it takes for you to breath, circulate blood, regulate hormones, and much more.
Your resting metabolic rate accounts for approximately 60-70% of your total calories expended in a day. So, imagine you sat around, did not eat or drink anything, and watched TV all day. Your body would still burn a large amount of its daily calories.
2) Daily Activity is the second contributor to the total calories you burn each day. Sometimes these are broken down into non-exercise activity and exercise related activity.
Non-exercise would be your physical movement throughout the day. Exercise specific would be referring to the calories you burn during a workout or training session. At the end of the day... any movement will help you burn more calories each day.
3) TEF (Thermic Effect of Food) is the number of calories it takes your body to process the food you consume. Think about it, anything that takes your body effort or work, will cause more calories to be used.
So, when you eat a chicken breast, or any food, your body must use energy to digest it. Then push that food through the digestive system to absorb it properly.