How many calories do you burn in a day without exercise?

To answer this question, we must first estimate the calorie requirements of muscle tissue for each of us. Most people burn an estimated 15 percent of their body’s total mass just from living.

Theoretically, a large percentage of that energy should be burned by muscle, but the actual calorie needs for a normal human are difficult to estimate. In fact, some estimates have been made — but in different ways. Most people estimate 15 percent of the daily energy requirements were burned by muscle metabolism, although it’s possible to overestimate the figure if weight loss is included.

As it turns out, the calorie needs of muscle tissue are highly dependent on other functions. If you have a high metabolic rate and small body mass, muscle metabolism is likely your largest source of calories and you burn more because other body functions have less direct impact on metabolic activities.

What type of work do you normally do? Muscle metabolism contributes to the metabolic processes in which you perform the bulk of your physical activities (e.g., running). But it’s also essential for your daily living, which includes bathing, cooking, laundry, cleaning, etc. In particular, your body uses your muscle mass to mobilize fat as you do this work. It’s thus possible to have a metabolism of 50 percent protein and 50 percent carbohydrate metabolism. But if you’re a sedentary male, your diet tends to be comprised of high fat/low protein and low sugar foods.

The Mayo Clinic Diet: How It Works and What to Know | Everyday Health
How is your weight held? One study measured the relative percentage of total body fat in more than 100 normal-weight young men. They measured the percentage of muscle mass, fat mass (total body), and percentage of body fat. This is an accurate and repeatable way to estimate the percentage of total body fat. For instance, if muscle mass is 50 percent, and body fat 25 percent, you weigh 80 percent fat. If you are a healthy normal weight male, with total body mass 100 pounds, your percentage of fat is 15 percent. The percentage of fat that you hold has three important meanings. First, it tells you whether you will gain weight if you lose weight, thereby affecting your percentage of body fat. Second, it tells you how much fat your body has, relative to your total body mass. Finally, it tells you how well your body uses stored fat as fuel, which controls your body’s need for insulin in order to make the necessary blood glucose for glucose synthesis. The proportion of fat you hold can be significantly lower if your diet is not sufficient to provide adequate calories.