How to calculate the correct calorie content of a diet?

When changing your eating habits, cutting back on sweets and salty snacks, and adding physical activity don't help you lose those extra pounds, it's worth precisely determining your energy requirements and then estimating how many calories you should actually consume per day to reach your goal. Only by consuming fewer calories than your body burns throughout the day will you get closer to your dream physique.

How do you calculate your requirements?

The basis for calculating your calorie needs is determining your Total Daily Energy Expenditure (TDEE). To calculate your TDEE, you should first calculate your Basal Metabolic Rate (BMR) and then multiply it by the appropriate physical activity factor. So:

Total Daily Energy Expenditure (TDEE) = Basal Metabolic Rate (BMR) x Physical Activity Factor

Now, let's explain what these individual elements are. BMR is the minimum level of energy expenditure occurring in the human body. Energy from BMR is used to maintain basic life processes, such as breathing, blood circulation, and heart function. You can use the Harris-Benedict or Mifflin equations to calculate your BMR.

Mifflin equation:

• BMR (women) = (10 x weight [kg]) + (6.25 x height [cm]) - (5 x [age]) – 161
• BMR (men) = (10 x weight [kg]) + (6.25 x height [cm]) - (5 x [age]) + 5

Harris-Benedict equation:

• BMR (women) = 655.1 + (9.563 x weight [kg]) + (1.85 x height [cm]) – (4.676 x [age])
• BMR (men) = 66.5 + (13.75 x weight [kg]) + (5.003 x height [cm]) – (6.775 x [age])

And what is physical activity? Contrary to appearances, this term doesn't just mean gym workouts or playing sports. Physical activity also includes walking, taking the stairs, and even doing household chores – you burn calories doing these, too!

 The following activity factors are generally accepted:

• 1.2 – 1.3 –> for bedridden patients
• 1.4 –> for low physical activity
• 1.6 –> for moderate physical activity
• 1.75 –> active lifestyle
• 2 –> very active lifestyle
• 2.2–2.4 –> professional sports

Dietary calorie intake depends on your goal

Once you have calculated your TDEE, you should adjust the calorie content of your nutrition plan based on your intended goal. If you want to gain weight or build muscle mass, you add a specific number of calories to your TDEE. This is often around 200–300 kcal more per day. We do the opposite when we want to lose weight. In that case, you should subtract some calories from your TDEE, depending on your starting weight and physical activity level. It is usually recommended to "cut" about 300–600 kcal, or even 1000 kcal per day for obese individuals. Another approach is to reduce your TDEE by 10–20%.

But be careful! You shouldn't judge the potential final result based on the first few weeks of a diet, when weight loss is significantly higher. Weight loss should be gradual and steady (this usually happens only in the later stages of dieting), with a drop of about 0.5–1 kg per week. It also happens that weight loss is not noticeable on the scale, but is clearly visible when measuring body circumferences (e.g., thighs, calves, waist, or abdomen).

Expert confirmation

For a diet to achieve its intended goal, the calorie content of the plan should be calculated individually. While using the formulas mentioned above should not be a major problem, estimating the appropriate activity level can cause uncertainty and lead to significant errors in calculations. Therefore, it is always worth consulting your requirements with an experienced dietitian.

Bibliography:

• Gawęcki J. (ed.): Human Nutrition, Fundamentals of Nutritional Science. PWN Scientific Publishers, Warsaw, 2012
• Jarosz M., Rychlik E., Stoś K., Charzewska J. (eds.): Nutritional Standards for the Polish Population and Their Application. National Institute of Public Health - National Institute of Hygiene, 2020
• Bean A.: Sports Nutrition: A Complete Guide. Zysk i S-ka Publishing, 2014