If there was one thing to measure as the foundation to any health programme, I would argue that it should be Basal Metabolic Rate or BMR.
Basal Metabolic Rate
BMR is the minimum amount of energy required to maintain basic bodily functions e.g. sleep. It is determined by the amount of metabolically active tissue e.g. muscle mass, and can be calculated easily from a handful of simple measures.
BMR makes up about three quarters of your energy use at around 1 kcal per minute. It is affected by body size, age and gender as well as lean muscle mass. The larger the muscle mass the more kcal are used for the active tissue so by increasing muscle mass you can increase BMR and by decreasing muscle mass will decrease BMR.
Total Energy Expenditure
But hopefully we don't just lounge around all day sleeping. Our true energy requirements are determined by three other elements as outlined in the diagram below:
The Thermal Effect of Food (TEF) represents the energy required to digest food - metabolism requires energy.
General Daily Activity (GDA), sometimes called Non-Exercise Activity Thermogenesis (NEAT), represents the energy required to carry out general activity that is not specific exercise training.
Physical Activity & Exercise, makes up the rest. This is the most dynamic element of daily energy requirements and is significantly impacted by daily routines as well as specific training session or tasks.
BMR represents 40-70% of your daily energy needs and TEF represents 10-15% with the rest being determined by your overall level of activity and the time spent and intensity of exercise.
Both BMR and TEE are influenced by body size with larger people having more tissue mass and a higher BMR. Fat Free Mass or FFM is made up of muscle, bones, skin and organs is more metabolically active than the remaining Fat Mass or FM.
The most commonly used equation to calculate BMR is the Harris-Benedict equation. However, in 1990, a study by Mifflin MD and St Jeor was published in the American Journal of Clinical Nutrition. It proposed a new predictive equation for resting energy expenditure in healthy individuals, suggesting an update to the existing Harris-Benedict method.
The Mifflin-St Jeor equation was said to be more predictive for modern lifestyles and has been establishing itself as the standard for calculating BMR but both equations are still in common use today.
Like the Harris-Benedict method, the Mifflin-St Jeor model uses a different formula for females versus males.
Once you've calculated your BMR, there's a number of ways to calculate your daily calorie requirement but the simplest method is to use Physical Activity Level (PAL) ratios.
TEE = BMR x PAL
PAL's are broken into 5 levels ranging from Sedentary to Extremely active and combine the effects of the Thermic Effect of Food, General Daily Activity and Physical Activity & Exercise.
To estimate your energy expenditure using this method simply multiply your BMR by appropriate activity level.
As you can see, your actual energy expenditure can cover a large range depending on your general activity levels of your lifestyle as well as the amount of physical training you do on a given day.
Therefore, by estimating and becoming familiar with your personal daily energy requirements, you will be much better enabled to determine the amount and types of energy intake you require to meet the specific goal or outcome you are looking to achieve.
A good rule of thumb is to calculate your TEE for levels 1, 3 and 5 and once you know these numbers:
- Don't regularly exceed Level 1 on days that you aren't training.
- Aim for Level 3 for days you are training.
- Save Level 5 for big training days, race day or whenever you need to be well fuelled.
There are more advanced methods such as True TEE that we use with professional athletes and expedition teams in particular that can produce very granular estimates of energy needs. These methods allow us to adjust details like format, portion size, macronutrient makeup and timing to maximise performance whilst minimising weight and bulk.
If this blog has piqued your interest in energy balance you might like to read about how to apply different fuelling strategies in this blog.
To complete a personalised True TEE assessment and work out accurate measurements of your energy requirements for any event, challenge or expedition contact our coaching team at firstname.lastname@example.org or sign up for one of our nutrition planning sessions such as this one.
You can download a free BMR calculator here.