Calorie expenditure is the amount of energy the body uses in a certain period of time. Everything the body does requires energy. Even while sleeping, the body is still performing myriad processes, including breathing, digestion, and healing. The calorie expenditure is different for each activity and each individual, depending upon a number of factors including age, weight, and gender.
A “calorie” is simply a unit of measure used in relation to the body’s energy usage, with that energy coming from food intake. When a food is listed as having 300 calories, that means it contains 300 units of energy. When an activity is said to burn 300 calories, that means the body uses 300 units of energy to complete the activity.
Estimating calorie expenditure is important for many different reasons. Doctors use it to determine how much nutritional support critically ill patients need. Bodybuilders use it to determine how much food to eat in order to promote muscle growth, and dieters use it to determine how much food to eat to promote fat loss. The base calculation is called the Total Daily Energy Expenditure (TDEE), and is the total energy the body needs to function throughout a 24 hour period. A caloric intake below the TDEE will result in weight loss, and a caloric intake above the TDEE will result in weight gain.
There are many different methods of determining TDEE, with varying degrees of accuracy. The easiest method for individuals looking for a rough estimate is to multiply the body weight by 15. The result is a very basic estimation of TDEE that is most likely not very accurate. Many factors are important to consider when calculating caloric needs and expenditure, including body composition.
The Harris Benedict equation is the one widely used by doctors and fitness professionals because of its overall accuracy. This method takes many factors into account, including basal metabolic rate (BMR), which is the body’s calorie expenditure just for performing basic bodily functions, excluding physical activity. In addition, the calculation involves an “activity multiplier.” which fine-tunes for physical activity.
First, the BMR is calculated differently for men and women:
Men: BMR= 66+ (13.7 x weight in kg) + ( 5 x height in cm) - (6.8 x age in years)
Women: BMR= 655+ (9.6 x weight in kg) + (1.8 x height in cm) - (4.7 x age in years)
Next, the BMR is multiplied by the activity multiplier, which ranges on a scale from a value of 1.2 for a sedentary person to a value of 1.9 for a professional athlete. For example, if a 32-year-old woman was 5’4” ( about 1.6 meters) tall, weighed 130 pounds (about 59 kg), and did moderate exercise four days per week, the equation would be:
BMR=655 + (9.6 x 59 kg) + (1.8 x 162.6 cm) - (4.7 x 32) = 1363.68
TDEE = 1363.68 x 1.6 = 2181.888
The Harris Benedict equation is accurate for most people, but because it does not take lean body mass into account, it is not accurate for the extremely muscular and the extremely obese. For these two groups, doctors use the Katch-McArdle formula, which is the same for both men and women:
BMR = 370 + (21.6 x kg lean mass)
The Katch-McArdle formula relies on doctor-determined body composition data to form a more accurate picture of the daily caloric needs of these patients.
How Calories Work
A calorie is a measure of the energy in food and drink. If you eat more calories than your body needs to burn for day-to-day functioning, those calories are stored in your body as fat. If you eat too many calories over time, you’ll gain weight.
The amount of calories you need varies widely depending on gender, current weight, activity level and general fitness. Generally speaking, men need 2,000 to 3,000 calories per week, or 286 to 429 per day, to maintain their weight. Women only need 1,600 to 2,400 calories every week, or 229 to 343 per day to keep their weight stable.
Our bodies burn calories even when we’re asleep. Calories are used to fuel autonomic processes — things your body does without you thinking about it, such as keeping your heart beating, breathing, digesting food and healing itself.
Physical activity burns more calories, so you need to adjust the number of calories you consume based on your activity level. For example, if you go for a one-mile run, you may burn about 100 calories. You’d need to increase your caloric intake by 100 calories to make sure you have the energy to do other things.
Good Calories Versus Bad Calories
You might think that a calorie is a calorie, and that’s all there is to it. However, there is a marked difference between good calories and bad calories. The key component to keep in mind is the ratio of calories to nutrients in those calories.
Good calories can come from high-fat, high-calorie foods. They contain lean proteins from chicken or pork; healthy fats from avocados and salmon; and healthy carbohydrates, or carbs, from whole grains and vegetables.
Bad calories don’t provide any nutrition to your body. They include foods such as processed foods, artificial ingredients, refined flours, unhealthy fats and sugar. Low calorie meals may not always be the healthiest if they include any of these sources of bad calories.
How To Calculate Calorie Deficit
You might want to lose weight instead of just maintaining where you’re at now on the scale. In that case, you need to calculate your calorie deficit, so that your calorie expenditure is greater than your caloric intake.
The first step is to figure out how many calories you need every day to maintain your weight. If you’re moderately active, take your weight and multiply it by 15. That will give you a rough estimate of your maintenance calories. If you weigh 175 pounds, you’d need 2,625 calories per week, or 375 per day, to maintain your weight.
Next, you need to determine your calorie deficit. According to the American Heart Association, you need to consume 500 fewer calories to lose one pound per week. To maintain your health, don’t cut your calories back too far; losing one to two pounds every week is safe. If you lose too much weight too fast, it can cause health problems. If you weigh 175 pounds, you’d need to consume 2,125 calories weekly, or 304 calories daily.
Calories Needed To Gain Weight
Being underweight can lead to a host of health problems. These include impaired immune system function, lower fertility, osteoporosis and an increased risk of dementia. To avoid these issues, you may decide to reach a healthier weight.
If you want to gain weight, you’d want to reverse the deficit numbers. For example, if you weigh 100 pounds and want to gain 25 pounds, you’d need to take in 1,500 calories each week, or 214 every day, to maintain your weight. To safely gain one pound per week, you’d add 500 calories to your diet, for a total of 2,000 weekly calories, or 286 daily.
Calories Needed for Muscle Gain
To gain muscle mass, you also need to increase your caloric intake. You should take in 20 more calories per pound of your current weight. If you weigh 150 pounds, you’d need 2,250 calories per week, or 321 per day, to maintain your weight.
You need a steady supply of energy to build muscle mass, so instead of eating three meals a day, you’d have 6 or so smaller meals spaced evenly throughout the day. Protein is used to build muscles, so it’s important to consume plenty of that, followed by complex carbs, and finally healthy fats.
It’s important that you consume more good calories than bad. If you want to gain or lose weight, or gain muscle mass, it becomes important to keep track of your day-to-day caloric intake. With careful monitoring of the calories you consume and burn, you can reach your weight goals.