The Stored Chemical Energy in the Food and Human Body
Before describing what total daily energy expenditure is, let’s talk a little about energy itself. Energy represents the capacity to do work. The sun is the ultimate source of energy. Through the photosynthesis process, plants use solar energy to produce stored chemical energy in the form of either fats, carbohydrates, or proteins. Animals eat these plants and use and store the plants’ stored chemical energy for their own. After consumption of plant and animal foods by humans, fats, carbs and proteins in the foods undergo some metabolic changes and are utilized to develop body structure, to regulate body functions, or to provide a storage form of chemical energy in the body.
The energy in the body is available for immediate use in the form of adenosine triphosphate (ATP). ATP is an organic complex compound constructed with high-energy bonds, which, when split by enzyme action, can release energy immediately for several body functions, such as muscle contraction, nerve impulse propagation, condensate dissolution, and chemical synthesis. To transfer energy in the renewal of ATP, humans rely on food. The amount of food we eat and then use as energy has significant effects on our fitness, health and performance. For this reason, energy balance in the body is an important matter in good nutrition.
What is Total Daily Energy Expenditure or Metabolic Rate, Body’s Need for Energy?
You may already know that metabolism is the total amount of energy required for our physiological functions and processes that take place within the body. During rest and physical activities, every cell, to do its job in the body, consumes and regenerates ATP every second. The total energy consumed by the trillions of cells in the body in the sleep and awake state during a day is called total daily energy expenditure or metabolic rate. The total daily energy expenditure is generally classified into five metabolic components.
- Basal metabolic rate (BMR)
- Resting metabolic rate (RMR)
- Thermic effect of feeding (TEF)
- Exercise Activity
- Non-exercise activity thermogenesis (NEAT)
Let’s now explain clearly each of the metabolic components and their relation to the total daily energy expenditure.
Basal Metabolic Rate (BMR)
The BMR is the amount of energy that is necessary to keep you alive when you are awake, not sleep. Indeed, it’s the minimum amount of energy expenditure required to sustain the vital functions of the human body. BMR accounts for over 70% of the total daily energy expenditure or metabolic rate.
Resting Metabolic Rate (RMR)
The RMR is the amount of energy that is necessary to keep you alive and sustain the body’s vital functions when you are asleep, not awake. Factors such as recent movements and recent food ingestion impact the measure of RMR to be 10% higher than the BMR.
Thermic Effect of Feeding (TEF)
The TEF is the amount of energy necessary to transport, absorb, store and metabolize the food we consume. The TEF varies based on which macronutrients we ingest. Fat has the lowest thermic effect and protein has the highest thermic effect. It usually lasts three to four hours, and the peak time is about 1 hour after a meal. In general, TEF accounts for 10% of the total daily energy expenditure or metabolic rate.
It’s the amount of energy you consume during purposeful training sessions. Since daily energy expenditure is variable from person to person, the amount of energy sedentary people consumes in exercise activity accounts for 10% to 15% of the total daily energy expenditure or metabolic rate and 30% or more for physically active people.
Additionally, a high-intensity training session not only creates energy demand within a session but also creates a higher energy demand after a session. This increases post-exercise oxygen consumption, which is helpful for weight loss. In other words, post-exercise oxygen consumption increases the total daily energy expenditure or metabolic rate (metabolism). Since high-intensity training is very demanding, you should allow your body to get fully recover for optimal performance before another training session.
Non-Exercise Activity Thermogenesis (NEAT)
The NEAT is the amount of energy we consume for unplanned and/or light activities that are not sleeping, eating, or exercise movements and takes place every day. NEAT includes such activities as typing on a keyboard, housework, washing, moving your head and hands, playing with a kid, etc. Although NEAT contributes to a small amount of the total daily energy expenditure or metabolic rate, yet is an important indicator of weight loss as well as weight gain.
Estimation of Total Daily Energy Expenditure/Metabolic Rate/Metabolism
There are many methods to estimate total daily energy expenditure or metabolic rate. Some of them, such as Indirect Calorimetry and Direct Calorimetry, provide accurate measurements, but they need large, expensive environmental chambers that just a few research centres can afford such facilities.
On the other hand, though less accurate, there are some other methods that are practical and predictive for everyday use to estimate the total daily energy expenditure or metabolic rate. These methods have been described below are based on age, weight, and height.
Mifflin Equation for RMR
This equation is based on the height in cm and weight in kg.
RMR (kcal/day) = [(10 x weight in kg) + (6.25 x height in cm) – (5 x age in years) + 5]
RMR (kcal/day) = [(10 x weight in kg) + (6.25 x height in cm) – (5 x age in years) – 161]
Owen Equation for RMR
This equation is based on the weight in kg.
RMR (kcal/day) = [879 + 10.2 (weight in kg)]
RMR (kcal/day) = [795 + 7.2 (weight in kg)]
Harris-Benedict Equation for RMR
This equation is based on the weight in kg, height in cm, and age in years.
RMR (kcal/day) = [66.5 + (13.75 x current weight in kg/adjusted weight in kg) + (5.0 x height in cm) – (6.76 x age in years)]
RMR (kcal/day) = [655 + (9.56 x current weight in kg/adjusted weight in kg) + (1.85 x height in cm) – (4.68 x age in years)]
You can estimate RMR for an ideal weight when weight loss is the goal in the Harri-Benedict Equation. Indeed, there is a sub equation within the main equation. To adjust your ideal weight, use the following equation and then add it to the main equation mentioned above.
Adjusted Weight (in kg) = [(actual body weight in kg – ideal weight in kg) x 0.25] + ideal weight (in kg)
Note: The Mifflin equation in comparison with the Owen and Harris-Benedict Equations was more closely predictive of resting metabolic rate (RMR) when compared to indirect calorimetry in a study carried out for validation of these established equations on obese and non-obese people.
Estimating the Total Daily Energy Expenditure/metabolic rate in Practice
Generally, total daily energy expenditure (metabolic rate) is defined by RMR (represents BMR + maintenance activity) + physical activity (exercise activity + NEAT) + TEF.
Since your RMR, Physical Activity, and Thermic Effect of Feeding (TEF) account for 60% – 75%, 15% – 30% and 10%, respectively, you can multiply the estimated RMR by the total percentage of physical activity + TEF to estimate the total physical activity + TEF energy expenditure in Kcal.
For example, your estimated RMR is 1600 Kcal by Mifflin Equation. Now, to estimate the total daily energy expenditure (TDEE)/metabolic rate, we can estimate physical activity plus TEF total energy expenditures based on the estimated RMR. To do so, the percentage for physical activity (exercise + NEAT) can be 15% – 30% (low to high-intensity training) and for TEF is 10%, and it can be 25% – 40% totally. So the estimation of the total daily energy expenditure (TDEE) equals RMR + (RMR * 0.25%- 40%).
Example 1: for 25% (of physical activity+ TEF)
Estimated RMR = 1600 Kcal
TDEE = RMR + (RMR * 0.25%- 40%)
TDEE = 1600 + (1600 * 25%) = 1600 + (1600 * 0.25) = 2000 Kcal
2000 Kcal is the total daily energy expenditure/metabolic rate.
Example 2: for 40% (of physical activity+ TEF)
Estimated RMR = 2000 Kcal
TDEE = RMR + (RMR * 0.25%- 40%)
TDEE = 2000 + (2000 * 40%) = 2000 + (2000 * 0.40) = 2800 Kcal
2800 Kcal is the total daily energy expenditure/matabolic rate.
The two examples above could be more accurate for the general population, not for everyone, such as a highly active athlete, a bodybuilder, an obese, etc. One of the criteria for good nutrition is outcome-based. Based on your nutrition outcomes, you can adjust the estimated total daily energy expenditure/metabolic rate in a very optimal, easy way.
The Bottom Line
Note that no equation is perfect. In general, it’s acceptable for an equation to predict resting metabolic rate (RMR) to within 10% of the actual measured value. Also, note that even food labels are estimates, they are not actual. For this reason, following the numbers as though they are real can lead to frustration.
Energy balance is the relationship between the amount of energy you consume from food and drink “energy in as food calories” and the amount of energy being used in the body for all body functions and daily activities “energy out as calories“.
Energy imbalances impact more than weight gain or loss. Reduction in the metabolic rate impacts non-survival functions in the body such as metabolic function, cognitive function, reproductive function and repair function. On the other hand, not only gaining fat but also increasing blood pressure and blood cholesterol, building up plaques in arteries, becoming insulin resistant (predisposed to diabetes), inclined to certain cancers to name a few, are negative effects of too much overfeeding or positive energy imbalance.
It’s noteworthy that when you follow a good nutrition plan, your appetite more closely matches your total daily energy expenditure. But when the diet you normally eat doesn’t consist of whole and naturally occurring foods, your body’s functionality to regulate its dietary intake via hunger signals is adversely impacted. In most cases, when appetite cues are affected can lead to weight gain.