Scientific Macro Calculator

Information & Literature

The Formulas

Its worth making a point here that none of these formulas will give everyone who uses it the same level of accuracy, nor should they be used more than just a starting point, to then make adjustments from depending on where your body composition goes in relation to the goals you have set. Below im going to show you what the formulas are mathematically, point you towards where they came from then talk about their suitability and limitations. 

Harris-Benedict (Revised) - 1984

Male:   (13.397 * Bodyweight) + (4.799 * Height) - (5.677 * Age) + 88.362
Female: ( 9.247 * Bodyweight) + (3.098 * Height) - (4.330 * Age) + 447.593


The original Harris-Benedict formula (Harris and Benedict, 1918) is one of the oldest attempts at estimating metabolic rate, it shows a vast difference in BMR between the genders which may have been due to the difference in work related activity between men and women during that time. It was later revised by Roza and Shizgal, (1984). They found the difference in BMR between the genders to be less compared to the original equation. Its still generally seen as an outdated formula, but it does appear in some calculators on the internet still.

Mifflin St Jeor - 1990

Male:   (10 * Bodyweight) + (6.25 * Height ) - (5 * Age) + 5
Female: (10 * Bodyweight) + (6.25 * Height ) - (5 * Age) - 161


This formula is widely considered the most accurate for the average person, it uses body weight, height, age and gender to determine BMR. It was derived from data of 498 subjects (male and female, obese and normal weight) and BMR was measured using indirect calorimetry. The formula does fall short when it comes to very lean or very obese individuals as it can only presume the average level of bodyfat percentage held by the group of subjects in the study. So the extremes in terms of body composition can end up getting inaccurate estimates.

Katch-McArdle (Hybrid)

(370 * ( 1 - Bodyfat Percentage )) + (21.6 * (Bodyweight * (1 - Bodyfat Percentage))) + (6.17 * (Bodyweight * Bodyfat Percentage))

(McArdle, Katch and Katch, 2011) & (Sailrabbit.com, 2014)

The Katch-McArdle (Hybrid) is a variation on the original formula that can be found in the book released by McArdle, Katch and Katch (2011). The 'Hybrid' version was created by the author of this website, it provides more accurate estimates for leaner individuals as well as the average and overweight. I'd recommend checking out his site, its a very good resource for calculating energy expenditure and seeing the comparisons between the common formulas. 


Cunningham

500 + ( 22 * ( Bodyweight * ( 1 - Bodyfat Percentage ) ) )

I dont have any source literature on the Cunningham formula as of yet, I am still searching for it. It is similar to the Katch-McArdle formula in which it only uses Bodyweight and Bodyfat Percentage to calculate energy requirements. There is a slight difference though, the Cunningham formula calculates RMR instead of BMR, so it does produce a marginally higher value. I will define the difference betwen RMR and BMR below to offer some clarity on what I just said. 

BMR - Basal Metabolic Rate

This is a truer representation of your actual metabolic rate uninfluenced by digestion, exercise or just generally being awake for an amount of time. It is measured using gas analysis of calorimetry in a fasted state and immediately after waking from a prolonged sleep.

RMR - Resting Metabolic Rate

This is measured in the same way but without the conditions that are set with BMR, its slightly less accurate and will be higher than your BMR. But it could be more applicable to real world conditions.

 

Summary

Harris-Benedict (Revised)

Not really used anymore, outdated, only use for research purposes.

Mifflin St Jeor

The best formula for the average individual where body fat isnt too high or too low.

Katch-McArdle (Hybrid)

The most suitable formula where the individuals body fat is far from the average, to be used on people that are either very lean or obese.

Cunningham

Its quite popular within bodybuilding circles, should be used in a similar scenario to the Katch-McArdle but it will produce slighty higher estimates.


Protein Recommendations

I give two different protein recommendations in the calculator above, and there is good reason for this. The first protein recommendation is 1.2-2.2 g/kg of total bodyweight, this recommendation will only appear on the calculator when the user has programmed either a maintanence or a surplus of that maintanence. This coincides with a review paper by Helms, Aragon and Fitschen, (2014) where they stated that the collective agreement among reviewers is that a minimum protein intake of 1.2-2.2 g/kg is optimal to allow maximum muscle growth. A more recent study (Roberts et al., 2017) also showed during an isocaloric diet (a diet at maintanence calories) there was no significant difference in muscle recovery between a moderate intake of 1.8 g/kg of total bodyweight and high intake of 2.9g/kg of total bodyweight.

The second protein recommendation will pop up when you programme a deficit into the calculator. When you're in a calorie deficit, things get slightly different as muscle preservation or slight gains in muscle is the goal. This has been shown to require a higher level of protein.  Helms et al., (2014) suggest that 2.3-3.1g/kg of Lean Body Mass (LBM) is a good range to start with, scaling up as the deficit gets more aggressive.

 

References

Harris, J. and Benedict, F. (1918). A Biometric Study of Human Basal Metabolism. Proceedings of the National Academy of Sciences, 4(12), pp.370-373.

Helms, E., Aragon, A. and Fitschen, P. (2014). Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. Journal of the International Society of Sports Nutrition, 11(1), p.20.

Helms, E., Zinn, C., Rowlands, D. and Brown, S. (2014). A Systematic Review of Dietary Protein during Caloric Restriction in Resistance Trained Lean Athletes: A Case for Higher Intakes. International Journal of Sport Nutrition and Exercise Metabolism, 24(2), pp.127-138.

McArdle, W., Katch, F. and Katch, V. (2011). Essentials of exercise physiology. 4th ed. Lippincott Williams & Wilkins, a Wolters Kluwer business.

Mifflin, M., St Jeor, S., Hill, L., Scott, B., Daugherty, S. and Koh, Y. (1990). A new predictive equation for resting energy expenditure in healthy individuals. The American Journal of Clinical Nutrition, 51(2), pp.241-247.

Roberts, J., Zinchenko, A., Suckling, C., Smith, L., Johnstone, J. and Henselmans, M. (2017). The short-term effect of high versus moderate protein intake on recovery after strength training in resistance-trained individuals. Journal of the International Society of Sports Nutrition, 14(1).

Roza, A. and Shizgal, H. (1984). The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. The American Journal of Clinical Nutrition, 40(1), pp.168-182.

Sailrabbit.com. (2014). SailRabbit: BMR, TDEE and BMI Calculator. [online] Available at: https://www.sailrabbit.com/bmr/