Updated: Jan 2
Eating well is not only about eating the right food. It is also about consuming the right amount of calories. Calories (also commonly referred to as energy) are an important variable to consider when planning a nutritional plan. If we fail to consume sufficient energy, it can lead to an increase in fatigue, reduced performance in our work and training, a slower recovery in between workouts, loss of muscle, an increase risk of illnesses and injuries, and hormonal disruption for females. The number of calories that you need will depend on a number of variables including your gender, genetics, age, weight, body composition, and daily physical activity level. Luckily, there are very simple ways to calculate how much energy you need to consume.
First, you need to calculate your Resting Metabolic Rate (RMR). The resting metabolic rate describes the energy we burn during the state of rest. Even when we are doing nothing (for example when sleeping or sitting down), our body systems are still working to keep us alive. The heart is still beating and pumping up blood around the body, the lungs are still taking in new oxygen, the digestive system is still digesting food, etc. These systems use a considerable chunk of our energy (around 60-75% of all the calories used daily). Since men have a higher muscular body composition, the RMR for men tends to be higher. The resting metabolic rate is calculated using the following formulas:
Males: RMR (kcal/day) = 66.47 + 13.75 x Weight (kg) + 5 x Height (cm) - 6.76 x Age (yrs)
Females: RMR (kcal/day) = 655.1 + 9.56 x Weight (kg) + 1.85 x Height (cm) - 4.68 x Age (yrs)
For example, a 25-year-old, 60 kg female, with 165 cm in height, her RMR would be:
RMR (kcal/day) = 655.1 + 9.56 x Weight (kg) + 1.85 x Height (cm) - 4.68 x Age (yrs)
= 655.1 + 9.56 x 60 + 1.85 x 165 - 4.68 x 25
= 655.1 + 573.6 + 305.25 - 117
= 1533.95 - 177
= 1356.95 kcals/day
This means that this female’s body uses 1357 kcals/day during rest.
After calculating the resting heart rate you need to calculate your daily energy expenditure with physical activity during the day. In this case, physical activity refers not just to planned workouts, but may also include housework, walking to work, carrying the groceries, playing with the kids, running errands, etc. The number of calories you burn will vary on the type, duration, and intensity of the activity, as well as your weight. If you have an accurate sports watch it will tell you how many calories you burned daily. If you do not have a sports watch, you can simply calculate the daily energy expenditure by multiplying your RMR with the appropriate number in the statements below:
Mostly sedentary (little or no physical activity): RMR x 1.2
Fairly active (including walking and/or exercise 1-2 weekly): RMR X 1.3
Moderately active (regular brisk walking or mild physical activity 2-3 weekly): RMR x 1.4
Active (intense exercise for 3 or more times per week): RMR x 1.5
Very active (intense exercise every day) RMR x 1.7
If we continue with the previous example, if our female was moderately active, she would need to multiply 1357 (her RMR) by 1.4. Therefore:
Daily energy expenditure = 1357 x 1.4
= 1899.8 kcals/ day
Finally, you need to add the number of calories you further burned during your workout. Again a sports watch can give you an accurate estimate. Alternately, you can calculate how much calories you burned with the table below:
Therefore if our female walked for 30 mins at a speed of 5.5 km/hr, she would burn approximately 120 kcals. Therefore if we add this amount with her daily energy expenditure (1900 + 120) we find that this female requires 2020 kcals daily to maintain her body weight. If you want to lose weight, you need to eat less than that amount. If you want to gain weight you need to consume more calories than the daily energy expenditure.
Jagim, A. R., Camic, C. L., Kisiolek, J., Luedke, J., Erickson, J., Jones, M. T., & Oliver, J. M. (2018). Accuracy of resting metabolic rate prediction equations in athletes. The Journal of Strength & Conditioning Research, 32(7), 1875-1881.
Letter, H. H. (2004). Calories burned in 30 minutes for people of three different weights. Issue: July. https://www.health.harvard.edu/diet-and-weight-loss/calories-burned-in-30-minutes-of-leisure-and-routine-activities