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How to Calculate Your Calorie Intake (BMR and TDEE)

All this talk about calories and basal metabolic rate (BMR) has been theoretical so far, right? Previously, we discussed finding your calories, creating a calorie deficit, staying at maintenance calories, achieving fat loss, gaining muscle, and more. In this article, we provide tools to calculate the caloric requirements needed to maintain your body weight. You can adjust this number depending on whether you want to gain or lose weight. From there, you can determine your macronutrient ratio (how much protein, carbs, and fat you need).


Understanding BMR

BMR is the number of calories your body needs to sustain essential bodily functions without accounting for food or physical activity. This term is often used interchangeably with Resting Metabolic Rate (RMR).

The most accurate way to measure BMR involves using a metabolic cart or direct calorimetry, which measures oxygen consumption (VO2) and carbon dioxide production (VCO2) (1). However, this method is not practical or accessible for most people.

Indirect calorimetry relies on equations based on the laws of thermodynamics (2). Popular equations for estimating BMR include Harris-Benedict, Mifflin-St Jeor, Katch-McArdle, and others (3-5).


Choosing a BMR Equation

The top three BMR equations supported by scientific literature (2,3,6-9) are:

  1. Harris-Benedict Equation: Based on total body weight but tends to overestimate energy expenditure (10).
  2. Mifflin-St Jeor Equation: Introduced in the 1990s to address the Harris-Benedict equation's limitations (11). Suitable for modern lifestyles.
  3. Katch-McArdle Equation: Considers body composition, making it ideal for individuals with high muscle mass. However, its accuracy depends on precise fat mass measurements.


Mifflin-St Jeor Equation

  1. Men: RMR (kcal/day) = Weight (kg) x 10 + Height (cm) x 6.25 - Age x 5 + 5
  2. Women: RMR (kcal/day) = Weight (kg) x 10 + Height (cm) x 6.25 - Age x 5 - 161

Example: For a 27-year-old woman weighing 64 kg and standing 170 cm tall: RMR = (64 x 10) + (170 x 6.25) - (27 x 5) - 161 = 1406.5 kcal/day


Calculating TDEE

Total Daily Energy Expenditure (TDEE) accounts for energy burned beyond basic bodily functions. To calculate TDEE, multiply your BMR by an activity factor:

  1. 1.2 = Sedentary (little or no exercise)
  2. 1.375 = Light activity (exercise 1-3 days/week)
  3. 1.55 = Moderate activity (exercise 3-5 days/week)
  4. 1.725 = Very active (hard exercise 6-7 days/week)
  5. 1.9 = Extra active (hard exercise + physical job)

Example: If the woman’s activity factor is 1.55: TDEE = 1406.5 x 1.55 = 2180 kcal/day


Adjusting Calories for Goals

  1. Fat Loss: Subtract 10-25% from TDEE depending on desired weight loss speed.
  2. Muscle Gain: Add 10-15% to TDEE to create a caloric surplus.


Calculating Macronutrients

Each gram of macronutrients provides a specific caloric value:

  1. Protein: 4 kcal/gram
  2. Carbohydrates: 4 kcal/gram
  3. Fat: 9 kcal/gram
  4. Protein: Multiply body weight by 1.6-2.2 g/kg.
  5. Fat: Multiply body weight by 0.6 g/kg.
  6. Carbohydrates: Use the remaining calories after accounting for protein and fat.

Example:

  1. Protein: 64 kg x 2 = 128 g (512 kcal)
  2. Fat: 64 kg x 0.6 = 38.4 g (345.6 kcal)
  3. Carbs: (2180 - 512 - 345.6) / 4 = 330 g


Takeaway Message

Calculating BMR and TDEE helps estimate daily caloric needs, enabling precise adjustments for weight management. While equations like Harris-Benedict, Mifflin-St Jeor, and Katch-McArdle provide reliable estimates, individual factors and lifestyle variations should guide final adjustments.



References

  1. Metabolic Cart: Background, Indications, Contraindications. 2019 Jan 15 [cited 2019 Jun 6]; Available from: https://emedicine.medscape.com/article/2009552-overview
  2. Schoeller DA. The energy balance equation: looking back and looking forward are two very different views. Nutr Rev. 2009 May;67(5):249-54.
  3. de Luis DA, Aller R, Izaola O, Romero E. Prediction equation of resting energy expenditure in an adult Spanish population of obese adult population. Ann Nutr Metab. 2006;50(3):193-6.
  4. Frankenfield DC. Bias and accuracy of resting metabolic rate equations in non-obese and obese adults. Clinical Nutrition. 2013 Dec 1;32(6):976-82.
  5. This Is the Best TDEE Calculator on the Web (2019) [Internet]. Legion Athletics. 2019 [cited 2019 Jun 6]. Available from: https://legionathletics.com/tdee-calculator/
  6. Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy non-obese and obese adults: a systematic review. J Am Diet Assoc. 2005 May;105(5):775-89.
  7. Garrel DR, Jobin N, de Jonge LH. Should we still use the Harris and Benedict equations? Nutr Clin Pract. 1996 Jun;11(3):99-103.
  8. Frankenfield DC, Rowe WA, Smith JS, Cooney RN. Validation of several established equations for resting metabolic rate in obese and non-obese people. J Am Diet Assoc. 2003 Sep;103(9):1152-9.
  9. Boullata J, Williams J, Cottrell F, Hudson L, Compher C. Accurate determination of energy needs in hospitalized patients. J Am Diet Assoc. 2007 Mar;107(3):393-401.
  10. Roza AM, Shizgal HM. The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. Am J Clin Nutr. 1984 Jul;40(1):168-82.
  11. Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990 Feb;51(2):241-7.
  12. Human energy requirements [Internet]. [cited 2019 Jun 6]. Available from: http://www.fao.org/3/y5686e/y5686e07.htm#bm07.2
  13. Garthe I, Raastad T, Refsnes PE, Sundgot-Borgen J. Effect of nutritional intervention on body composition and performance in elite athletes. Eur J Sport Sci. 2013;13(3):295-303.