Calories and calorie requirements

How to calculate calorie requirements

What are calories?

Calories are the units of energy found in foods. Your body needs calories to fuel bodily functions and your physical activity. You get most of your calories from the macronutrients (carbohydrate, protein, and fat) that you eat. The calories are expressed in kilocalories (kcal). When people talk about calories, they usually mean kilocalories. One gram of carbohydrate provides four kilocalories, as does one gram of protein, whereas one gram of fat provides nine kilocalories.

What is basal metabolic rate?

Basal metabolic rate calculation
Figure 1. The basal metabolic rate calculation.

Your basal metabolic rate (BMR; Figure 1) is the number of kilocalories your body needs each day at rest. In other words, it’s the number of kilocalories your body needs just to maintain normal bodily functions, such as circulation, respiration, and temperature regulation. It does not include any physical activity.

BMR is very difficult to physically measure accurately. It requires a trip to a sophisticated lab, and lots of preparation, including approximately 12 hours of fasting to ensure that your digestive system is no longer active.

What is resting daily energy expenditure?

Resting daily energy expenditure (RDEE) is a less strict and less accurate measure of the number of kilocalories your body burns at rest. It is often used instead of BMR in scientific experiments because it is easier to physically measure (no need for fasting) and produces a value that is pretty close to your BMR. Because RDEE and BMR are so similar, they are often used interchangeably to mean the number of kilocalories your body burns at rest.

What is total daily energy expenditure?

Your total daily energy expenditure (TDEE) is the total number of kilocalories your body needs each day to fuel all of your bodily functions and all of your physical activity. Your TDEE is also known as your maintenance calories.

Why is your TDEE important when weight training?

The number of kilocalories you eat determines how your levels of fat and muscle might change as you train. Generally speaking:

  • if you consistently consume fewer kilocalories than your TDEE, you will lose fat and maybe a little muscle
  • if you consistently meet your TDEE, you will maintain your current level of fat (or maybe lose a little) and add muscle gradually
  • if you consistently consume more kilocalories than your TDEE, you will optimize muscle growth but also gain fat.

Therefore, you can manipulate your caloric intake to promote these different goals.

For people who are new to weight training, the story is a little different. Complete “newbies” seem to be able to gain muscle and lose fat at the same time almost no matter what they eat! However, as they become more experienced, gaining muscle and losing fat at the same time becomes increasingly difficult, and, just like the rest of us, they have to resort to phases of caloric surplus to gain muscle (known as bulking) and phases of caloric deficit to lose fat (known as cutting). Bulking and cutting are explained in detail in Bulking and cutting.

How do you calculate your TDEE?

Thanks to the advent of apps, you no longer need to calculate your TDEE. All you have to do is use an app to track your diet, and the app will tell you if you are in a state of caloric deficit, maintenance, or surplus. I explain how to track your diet in How to track your calories and diet. However, just in case you want to know how to calculate your TDEE manually, I explain it below. If you don’t want to know how to do it manually, then you can move on to Bulking and cutting.

How to manually calculate your TDEE

There are a number of manual ways to calculate your TDEE. The most accurate formulas take your lean body mass (also known as fat-free mass) into account. The most popular equation for calculating TDEE without knowing your lean body mass is the Harris–Benedict formula, and the most popular equation for calculating your TDEE using your lean body mass is the Katch–McArdle formula.

The Harris–Benedict formula

The Harris-Benedict formula of calculating TDEE involves two steps, one to calculate your BMR and another to multiply your BMR by an activity factor.

Step 1

Estimate your BMR. The formula is different for men and women.

Men: BMR = (10 x weight in kg) + (6.25 x height in cm) – (5 x age in years) + 5

Women: BMR = (10 x weight in kg) + (6.25 x height in cm) – (5 x age in years) – 161

Note: To convert pounds to kilograms, just divide the pounds by 2.2.

Step 2

Multiply your BMR by the appropriate activity factor in Table 1.

Level of physical activity Activity factor
Sedentary (little or no exercise) 1.200
Lightly active (light exercise/sports 1–3 days/week) 1.375
Moderately active (moderate exercise/sports 3–5 days/week) 1.550
Very active (hard exercise/sports 6–7 days/week) 1.725
Extra active (hard daily exercise/sports and a physical job, or training twice daily) 1.900
Table 1. Levels of physical activity and their corresponding activity factors.

The resultant figure is your TDEE—that is, the number of kilocalories your body needs each day to maintain your current weight.

Note: By not taking lean body mass into account, the Harris–Benedict equation assumes that you have an average amount of lean body mass. As a result, it is accurate for most people but not for those who are very muscular or overweight. For very muscular individuals, it will underestimate caloric requirements (because leaner bodies require more calories). For overweight individuals, it will overestimate caloric requirements (because it will assume that the individual has more lean muscle mass than he or she actually has). Therefore, if you have more than average muscle mass, you can compensate by adding 150 calories to your TDEE. Or, if you are obese, you can compensate by subtracting 150 calories from your TDEE.

The Katch–McArdle formula

Unlike the Harris–Benedict formula, the Katch–McArdle formula does require that you know your lean body mass. Because it takes lean body mass into account, it can be more accurate than the Harris–Benedict formula, especially for people who are very muscular or overweight.

The Katch–McArdle formula of calculating TDEE is the same for both men and women and involves two steps, one to calculate your RDEE and another to multiply your RDEE by an activity factor. Remember that your RDEE is practically the same as your BMR.

Note: I explained how to work out your body-fat percentage in How to track your progress.

Step 1

Calculate your RDEE. The formula looks like this:

RDEE = 370 + (21.6 x lean body mass in kilograms)

or, if you want to work with pounds:

RDEE = 370 + (9.79759519 x lean body mass in pounds)

You can work out your lean body mass by subtracting the weight of your body fat from your total body weight using this equation:

Lean body mass = (1 – body fat percentage expressed as a decimal numeral) x total body weight

For example, if you weigh 160 pounds and have 18% body fat, your equation would look like this:

1 – 0.18 = 0.82

0.82 x 160 = 131.2 lb of lean body mass

You can now plug your lean body mass into the above formula to get your RDEE, thus:

RDEE = 370 + (9.79759519 x 131.2) = 1,655

Step 2

Multiply your RDEE by the appropriate activity factor in Table 1. The resultant figure is your TDEE—that is, the number of kilocalories you have to consume each day to maintain your current weight.

Note: The problem with the Katch–McArdle formula is that it does not take age into consideration. As a result, it has been known to overestimate the caloric requirements of elderly individuals. Therefore, if you are over 50, and especially if you are over 65, you can compensate by subtracting 5% from your TDEE, or simply use the Harris–Benedict formula instead to calculate caloric requirements.

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