The question of how many calories do you burn just being awake refers to the energy required by the basal metabolic requirements of the human body. This means that even if you don’t move from the couch, you require calories to maintain the biological functions of your organs that keep you alive on a daily basis. So how many calories do you burn just living? It turns out that the answer depends, to a large degree, on your age. The resting metabolic rate decreases the older you get, which is why it is more difficult for older people to lose fat or gain lean muscle tissue.
If you are asking how many calories do you burn just living for one day, it may interest you to know that regular cardio (aerobic exercise) will not have a significant effect on your basal rate. This counter-intuitive result was demonstrated in a series of studies conducted in the 90s. However, these studies found that doing cardio past the “pain barrier” – usually above 20 to 25 minutes at 70% of your maximum heart rate (as dictated by your age) will temporarily increase your basal rate while your muscles are in recovery. More recent studies have also found that the answer to the question: how many calories do you burn at rest in day, is affected by anaerobic exercise. Lifting heavy weights to the point of secretion of lactic acid will have an effect on energy consumption.
Your basic rate of energy consumption is also affected by your weight. Miffin et al. introduced an improved version of the Harris-Benedict equation (1919) in 1990 – which takes the age, height and weight of the person in question into account in working out the basal metabolic rate. The equation is as follows:
Where BMR stands for Basal Metabolic Rate (kcal/day), W = weight (Kg), H= height(cm), A=age(years), and K is a constant which =+5 for men and -161 for women. This means that, for example, a 27 year old, 179 cm tall male who weight 82 Kg burns 820+1118.75-135+5 = 1808.75 kcal/day at rest. Just plug your individual numbers into the equation above to find out your BMR. More accurate forms of the equation above take the individual’s body fat percentage into account. Fat is not as metabolically active as muscle, and so requires less energy to remain active – this is why body builders require an especially high calorie intake during training.