Metabolism is the process by which the body changes food and drink into energy. During this process, calories in food and drinks mix with oxygen to make the energy the body needs.

Even at rest, a body needs energy for all it does. This includes breathing, sending blood through the body, keeping hormone levels even, and growing and repairing cells. The number of calories a body at rest uses to do these things is known as basal metabolic rate, also called basal metabolism.

Metabolism determines how much energy a body needs to operate, but weight also depends on how much a person eats and drinks combined with physical activity.

Muscle mass is the main factor in basal metabolic rate.

Basal metabolic rate depends on:

• Body size and composition. People who are larger or have more muscle burn more calories, even at rest.†

• Sex. Men usually have less body fat and more muscle than women of the same age and weight. That means men burn more calories.†

• Age. With aging, people tend to lose muscle. More of the body’s weight is from fat, which slows calorie burning.†

While every single person is different, a good generalization for basal metabolic rate can be made using the following formula:

• Men: BMR = 88.362 + (13.397 x weight in kg) + (4.799 x height in cm) - (5.677 x age in years)

• Women: BMR = 447.593 + (9.247 x weight in kg) + (3.098 x height in cm) - (4.330 x age in years)

Remember: this will give you BMR, which is how much your body will burn if you sit and do nothing.

Besides the basal metabolic rate, two other things decide how many calories a body burns each day:

• How the body uses food. Digesting, absorbing, moving, and storing food burn calories. About 10% of calories eaten are used for digesting food and taking in nutrients. This can’t be changed much.

• How much a body moves. Any movement, such as playing tennis, walking to a store, or chasing the dog, makes up the rest of the calories one burns daily. This can be changed a lot by doing more exercise and moving more during the day.

Daily activity that isn’t exercise is called nonexercise activity thermogenesis (NEAT). This includes walking around the house. It also includes activities such as gardening, housework, and even fidgeting. NEAT accounts for about 100 to 800 calories used daily.

You gain weight when you eat more calories than you burn - or burn fewer calories than you eat.

You lose weight when you eat fewer calories than you burn - or burn more calories than you eat.

For an average person, the amount of calories you can burn daily can be ballparked by multiplying your weight in pounds x 15.

If you’d like to get started with weight loss, multiply your weight in pounds by 15, then subtract 500. A pound of weight is roughly equivalent to 3,500 calories, so this should, in theory, help support weight loss of 1lb per week, which is typically considered a healthy, sustainable rate of weight loss.