Understanding how many calories your body needs per day can be tricky and there are plenty of equations out there that supposedly allow you to measure how many calories your body burns at rest. But are these equations accurate and if yes, which one is the best?
What did they test? The authors reviewed the current literature to examine the accuracy of resting metabolic rate prediction equations in athletes.
What did they find? Overall, the Ten-Haaf equation (based on age, weight and height) was the most accurate although it did not differ massively from other commonly used equations.
What does it mean for you? Using specific resting metabolic rate equations can give you a solid estimate in regards to how many calories your body burns at rest with the Ten-Haaf equation being the most accurate.
What’s the Problem?
Knowing how many calories one’s body uses on any given day is something that almost everyone wants to know at some point, regardless of being a fitness enthusiast or not. From smartwatches and devices to online calculators, there are a lot of ways to go about figuring out how many calories your body needs in order to maintain its weight. However, it’s not necessarily clear whether one method is better than the other at giving you a rough resting metabolic rate estimate, which you can then use to calculate your total daily energy expenditure (TDEE).
The component of one’s TDEE is their resting metabolic rate, which accounts for 60-70% of their energy expenditure, with the rest coming from physical activity and from the thermic effect of food (ie: how many calories your body uses to process the food you consume).
The best way to measure your RMR is via indirect calorimetry which measures how much oxygen you breathe in and carbon dioxide you breathe out to calculate how many calories your body is using, which can provide insights into your energy needs.
Most online calculators and fitness trackers calculate TDEE by estimating your RMR using a variety of equations that require you to input your age, height, weight and sometimes body fat percentage and then multiply that by an activity factor that best describes your daily activity levels (eg: active, sedentary etc). For example, the somewhat “known” website ‘tdeecalculator.net’ uses the Mifflin-St Jeor equation 1 for most RMR calculations but uses a different equation, ie: the Katch-McArdle equation, when a user chooses also to input body fat percentages
Examples of the two equations often used to calculate RMR:
Mifflin-St Jeor equation
Men: (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) + 5
Women: (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) - 161