what's behind calculatING BMR–TDEE?

As mentioned on the BMR-TDEE Calculator page, if you're keen on losing weight or building muscle, then it's wise to track and understand your progress. I normally advise doing this for at least for the first 1-3 months. There are a number of calorie tracking apps on the market.

After this period of familiarization, you could actually graduate to instinctive eating.

As I mention throughout this Site, you don't have to measure and monitor every step of your fitness journey. If you've already achieved a goal via one or other fitness program, you're probably well-accustomed to your nutrition and exercise needs.

So, depending on your future goals, you could merely make periodic checks and recordings – or you could more regularly track your progress. 

There are many different fitness-requirements across the spectrum from couch potato to the pro bodybuilder.

It's going to depend on you.

THESE DAYS, there's much hype about calculatING BMR AND TDEE. BUT do you actually know what THEY are?

BASAL METABOLIC RATE (BMR)

BMR should not be confused with BMI, which is a measure based on the mass and height of an individual. Instead, BMR is a measure of the energy needed to sustain your vital functions in a waking state (roughly two-thirds of your total energy expenditure).

Ideally, BMR is obtained by gauging the respiratory quotient (RQ) while in a motionless and non-digestive state. This is done in a controlled environment after 12 hours of fasting and 8 hours of sleep. (RQ = oxygen-consumption/carbon-dioxide elimination.)

You'll agree that this procedure would be impractical and expensive - not to mention boring! We're fortunate though to have a selection of formulas to help us estimate BMR. We'll get to them in a minute.


NOTE: BMR is similar to RMR or Resting Metabolic Rate. The means of testing are the same, but RMR is measured under less stringent conditions than BMR. Although test subjects should be rested, they are not measured directly upon waking or in a fasted state.
Because of this, RMR normally delivers results around 10% higher than BMR. Due to the small difference between BMR and RMR, these terms are often used interchangeably in the health and fitness industries to mean the same thing under the term 'BMR.'

TOTAL DAILY ENERGY EXPENDITURE (TDEE)

This is also known as TEE, and is the sum of all your calorie needs over a 24-hour period to maintain your present weight.

It comprises these 4 components:

  • BMR – Basal Metabolic Rate. The internal heat (thermogenesis) generated while driving your vital functions;
  • TEF – Thermic Effect of Feeding (energy costs of processing the food you eat);
  • NEAT – Non-Exercise Activity Thermogenesis. Low-intensity movements like sitting, walking or standing. (Since NEAT represents a negligible contribution to TDEE, it isn't factored into the mathematical formulas on its own, but is instead taken into account as part of PAL.);
  • PAL – Physical Activity Level, corresponding to a factor best estimating the energy expended by an individual (see the corresponding table below).
 
 

Formulas for estimating BMR

Of the several models available for calculating BMR, the more contemporary are those established by Harris-Benedict, Mifflin-St Jeor and Katch-McArdle.

Both the Harris-Benedict and Mifflin-St Jeor equations estimate BMR by taking mass, gender, weight and height into account. Although the Harris-Benedict formula (established in 1919) was revised in 1984, it is the Mifflin-St Jeor formula of 1990 (around 5% more accurate), which is more widely accepted. The equation is:

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

However, both the Harris-Benedict, Mifflin-St Jeor equations are based on overall body weight, and therefore do not consider differences in metabolic activity between lean body mass and body fat. (This is significant, since muscle tissue is far more metabolically active than fat stores are.)

Katch-McArdle, on the other hand, predicts resting daily energy expenditure, (BMR for our purposes), by using ‘lean’ or fat-free mass. This formula is definitely preferred for the leaner person, if an accurate body fat percentage is known. See the equation below:

  • BMR = 370 + (21.6 x lean mass in kilograms)

Factoring physical activity into the equation to get TDEE

Now that we have the first part of the picture - the BMR, how do we calculate the remaining calorie-expenditure and obtain our TDEE?

As mentioned above, you need to factor in what you do in a day and add this to your BMR. This element is known as the Physical Activity Level (PAL).

As with BMR, there are various formulas used in the industry to establish PAL. Arguably though, the most trusted are those set out in the table below:

CATEGORY AND LEVEL ACTIVITY FACTOR
SEDENTARY - (Little to no exercise. Desk job.) 1.2
LIGHTLY ACTIVE - (Light exercise on 1-3 days a week or 2 hours of walking a day.) 1.375
MODERATELY ACTIVE - (Moderate exercise/sport on 3-5 days a week or 3 hours of walking a day.) 1.55
VERY ACTIVE - (Hard exercise/sport on 6-7 days a week or 4 hours of walking a day.) 1.725
EXTREMELY ACTIVE - (Hard daily exercise/sport and physical job including 5 or more hours of walking a day.) 1.9
 

All that remains now is to multiply your BMR by an appropriate activity factor, and you have your TDEE! 

Although you have the background and formulas on how to calculate BMR-TDEE, this calculator will give you the data in a matter of seconds!

It also provides you a means to calculate your future (or adjusted) TDEE, as well as your calorie and macronutrient-breakdown.

BMR–TDEE, future TDEE and macronutrient ratios

The BMR-TDEE calculator uses a 3-step process to:

  • Estimate your BMR and TDEE according to your current physical activity-level (PAL). The TDEE value corresponds to the amount of calories required to maintain your current weight.
  • Provide your future TDEE based on a pre-set or custom goal, to fulfil that goal.
  • Suggest macronutrient breakdowns to support your fitness-goals.

guidelines

TDEE

As a basic guideline for weight loss, you could consider a calorie-deficit of approximately 10% to be both safe and manageable. Muscle-gain on the other hand would require a calorie-surplus of 5% or more. Of course both these scenarios will depend on individual condition and needs.

Macronutrient ratios

In terms of setting your macronutrient ratios, there are a number of factors which play a role including your body type, gender, age and of course your objective. Even though you could go with these basic guidelines, you may find that you have better or worse tolerances for fats or carbs. My best advice is to monitor and record your progress over time, and you will come to understand your metabolism and general constitution's tolerances.

As a general tip, it's advisable to start with the protein ratio. It is commonly accepted by the fitness industry that physically active people require more protein than their non-active counterparts to support their fitness-needs. However, the fitness industry giants recommend absurd quantities of protein upwards of 1-1.5 grams per pound of body weight. On the other hand, according to the Academy of Nutrition and Dietetics, the average individual should consume 0.35 grams of protein per pound of body weight per day for general health.

There's a big difference between these two recommendations. How much is enough?

  • 0.75-1 gram per pound of body weight is generally sufficient to support hypertrophy (muscle-development). Higher levels can be warranted in certain cases where carbs are reduced, for example during a cutting phase;
  • Fat ratios are best kept between 0.35 and 0.50 grams per pound of body weight. Higher levels of fat are appropriate when carbs are reduced. Conversely, fat should be lower and carbohydrates higher for bodybuilding goals. Moderate levels of fat-intake are suitable for maintenance protocols.

IN CLOSING

Although the formulas discussed above were devised on the basis of scientifically sound procedures in testing and collecting data, one has to allow for margins of error due to research populations used, and for individual differences. 

Therefore, none of the predictive equations will be free of inaccuracies or potential error. Because of this, they may be found to over or under-estimate BMR-TDEE values.

However, if consistently applied and monitored, they can be used as effective guidelines and adjusted to the individual. Establishing a metabolic set-point is of significant help in monitoring calorie-expenditure to lose, maintain or add mass.

TDEE is arguably one of the most important pieces of information when preparing to lose weight or gain muscle, so that nutrition-intake and energy-output can be effectively adjusted in line with program goals. 

In plain words: you can only know where to go if you know where you are now. To get there, keep your eye firmly on your goal while sticking to your program and nutritional requirements.

Consistency is key!

REFERENCES

  • Berardi, J., Andrews, R.; Nutrition: The Complete Guide, Official Course Text for ISSA's Specialist in Fitness Nutrition Program, 1st ed., International Sports Sciences Association; 2009. Unit 4, Energy Balance in the Body; p. 106-112.
  • Frankenfield, David; Roth-Yousey, Lori; Compher, Charlene (2005). Comparison of Predictive Equations for Resting Metabolic Rate in Healthy Nonobese and Obese Adults: A Systematic Review. Journal of the American Dietetic Association 105 (5): 775–789.
  • Kazaks, A.G., Stern, J.S.; Nutrition And Obesity: Assessment, Management and Prevention. 1st ed. Jones & Bartlett Learning; 2012.
  • McArdle, W.D., Katch, F.I., Katch, V.L. eds. Exercise Physiology: Energy, Nutrition and Human Performance. 4th ed. Baltimore, MD: Williams and Wilkins; 1996.
  • McArdle, W.D., Katch, F.I., Katch, V.L.; Essentials of Exercise Physiology. 3rd ed. Philadelphia, PA: Lippincott Williams and Wilkins; 2006.
  • Mifflin, M.D.; St Jeor, S.T.; Hill, L.A.; Scott, B.J.; Daugherty, S.A.; Koh, Y.O. (1990). A new predictive equation for resting energy expenditure in healthy individuals. The American journal of clinical nutrition 51 (2): 241–247.
  • Roza, A.M.; Shizgal, H.M. (1984). The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. The American Journal of Clinical Nutrition 40: 168–182.
  • Human energy requirements: Principles and Definitions. Report of a Joint FAO/WHO/UNU Expert Consultation. Food and Agriculture Organization of the United Nations (2001). Retrieved 2016-02-01.