A common health trend is to count calories.
This is the process of logging the food and drinks we take in and calculating the calories consumed.
This is typically done to ensure that a calorie goal is being met.
A calorie deficit is the intake of fewer calories than we consume, usually to lose weight.
A calorie surplus is taking in excess calories, typically to aid in muscle growth and increase in mass.
The third goal is to take in maintenance calories, this is matching your calorie expenditure with your intake.
In order for this to be effective, we need to learn the science behind balancing the energy.
Basal Metabolic Rate
Your Basal Metabolic Rate (BMR) is also referred to as the resting metabolic rate. This refers to the energy expended through the physiological process of life. In simpler terms, if we were to remain in bed all day and not move an inch, the number of calories our body burns just remaining alive is your BMR. This includes things like brain, heart, and liver function.
We can estimate our BMR using the following equations.
Women: BMR = 655 + (9.6 x weight in kilos) + (1.8 x height in cm) – (4.7 x age in years)
Men: BMR = 66 + (13.7 x weight in kilos) + (5 x height in cm) – (6.8 x age in years)
Predicting Energy Expenditure
Many of us will use a smart watch or fitness tracker to estimate the calories we expend through activity and exercise. However, there are also formulas to help us, which many smart devices are programmed around.
The Harris-Benedict Equation is a formula that uses your BMR and then applies an activity factor to determine your total daily energy expenditure.
To determine your total daily calorie needs, multiply your BMR by the appropriate activity factor, as follows:
- If you are sedentary (little or no exercise): Calorie Calculation = BMR x 1.22.
- If you are moderately active (moderate exercise/sports 3-5 days/week): Calorie Calculation = BMR x 1.554.
- If you are very active (hard exercise/sports 6-7 days a week): Calorie Calculation = BMR x 1.7255.
- If you are extra active (very hard exercise/sports & physical job or 2x training): Calorie Calculation = BMR x 1.9
The Thermic Effect of Food
The thermic effect of food is the energy associated with the digestion, absorption, transportation, and storage of food. The energy required to digest each food type (its TEF) can be expressed as a percentage of the energy provided.
- Fat provides 9 calories per gram; its TEF is 0–3%.
- Carbohydrate provides 4 calories per gram; its TEF is 5–10%.
- Protein provides 4 calories per gram; its TEF is 20–30%.
Around 10% of the calories we consume through food are expended during digestion, absorption, transportation, and storage. We can add this to our estimates when calculating calorie intake and expenditure.