Although there is a multitude of factors that can affect your weight in either direction, there is definitely some truth behind the concept of the “calories in” versus “calories out” equation.
When we consider the “calories in” side, we are looking at any calories you are consuming through food or drink. It’s fairly easy to calculate how many calories you are eating in a day, so long as you are willing to measure your portion sizes and look up the nutrition facts.
However, the “calories out“ side of this simple energy balance equation is more complicated.
Referred to more formally as total daily energy expenditure (TDEE), the “calories out” portion is your total calorie expenditure in a day.
There are several factors that affect your total daily energy expenditure, and none of them are as easy to estimate as the calories you’re taking in. With that said, in this article, we will cover all the nuts and bolts of total daily energy expenditure, including the TDEE definition, factors that affect TDEE, and how to estimate TDEE.
We will discuss:
- What Is TDEE?
- How to Calculate TDEE
Let’s get started!
What Is TDEE?
As mentioned, TDEE stands for total daily energy expenditure. The TDEE definition encompasses all of the sources of caloric expenditure in a day, which means that your TDEE is an estimation of the total number of calories you burn in a day.
When it comes to your total daily energy expenditure, it’s important to remember that this number includes more than just the calories you burn during exercise.Instead, your TDEE is the sum of the calories burned due to your basal metabolic rate (BMR), the physical activity you do in a day for general activities (working, cooking, hygiene, etc.), deliberate exercise, and diet-induced thermogenesis.
How to Determine Your TDEE
Let’s look at each of the factors that contribute to your TDEE.
Your basal metabolic rate (BMR) refers to the number of calories you burn at rest just to keep your body alive.
In other words, your BMR is the number of calories your body must burn at a bare minimum for basic (basal) functions like breathing, maintaining a heartbeat to circulate blood to your tissues, and processing nutrients.
You will sometimes hear the term “resting metabolic rate” (RMR) used interchangeably with BMR, though RMR is a slightly higher number that denotes the number of calories you burn per day resting with a few more normal, healthy functions above the do-or-die level of BMR.
There are several factors that determine your BMR, namely your body weight and body composition, your sex, your age, and your training status.
In terms of body size and composition, the larger you are (the more you weigh), and the more lean mass you have relative to body fat, the higher your BMR will be.
To make two simple comparisons, someone who weighs 90 pounds will have a lower BMR than someone who weighs 160 pounds, while someone weighing 180 pounds with 11% body fat will have a higher BMR than someone who also weighs 180 pounds but has 28% body fat.
In terms of sex, males typically have a higher BMR than females, largely due to differences in lean body mass and the relative size of metabolically-active organs like the liver.
BMR decreases with age, dropping more notably in aging seniors, largely due to sarcopenia (muscle loss).
In terms of TDEE, your BMR usually constitutes not only the highest percentage of the total energy expenditure per day relative to the other sources of calories burned but also the overall majority of your TDEE.
The American Council on Exercise reports that your BMR represents about 60-75% of the total calories you burn in a day, though it depends somewhat on how active you are both in terms of planned exercise as well as physical activity accumulated as you go about your day.
The more active you are above “basal” or resting conditions, the smaller the overall contribution your BMR will have on your total daily energy expenditure.
For example, let’s compare two different women who both have a BMR of 1,200 calories.
For simplicity, we will ignore the contribution of diet-induced thermogenesis to TDEE by assuming both our hypothetical subjects have the same daily calorie expenditure from diet-induced thermogenesis.
Let’s imagine person A is a marathon runner who regularly burns about 600 calories a day in her workouts. On top of this, she’s a busy school teacher who is on her feet most of the day.
As a result, she might burn 1200 calories above her BMR every day, bringing her total daily energy expenditure to 2400 calories.
In this case, her BMR constitutes 50% of her TDEE.
On the other hand, person B is relatively inactive, though she does low-intensity yoga workouts most days of the week.
In these workouts, she burns 150 calories, but for the rest of the day, she is relatively sedentary, doing only light housework and taking her dog for brief walks.
Based on her activity level, she might burn only 600 calories per day above her BMR.
Therefore, her TDEE is only 1,800 calories per day, with her BMR comprising 67% of her total energy expenditure.
Unless you go to a physiology lab for metabolic testing, you have to estimate your BMR.
Although there are several popular RMR equations, a study comparing the most common RMR formulas (Harris-Benedict, Mifflin-St Jeor, Owen, and World Health Organization/Food and Agriculture Organization/United Nations University [WHO/FAO/UNU]) found that the Mifflin-St Jeor was the most accurate.
The Mifflin-St Jeor Equation can be used to calculate RMR, which is close enough to BMR to be used as a substitute.
Moreover, this RMR formula is considered to be accurate within 10% of measured resting metabolic rate.
The Mifflin-St Jeor formulas for each sex are as follows:
Men: 10 x weight (kg) + 6.25 x height (cm) – 5 x age (y) + 5
Women: 10 x weight (kg) + 6.25 x height (cm) – 5 x age (y) – 161
Various factors of your workout affect how many calories you will burn for this aspect of your TDEE, and it will likely change day to day based on the specific workout you do.
The type of exercise, length of the workout, and intensity of your effort are the key factors that influence the number of calories you burn by exercising.
The exercise portion of your total energy expenditure is highly varied, depending on your training status. It might be anywhere from a few hundred calories per day to upwards of 1,200 calories or more.
For competitive athletes, the EAT section of the TDEE may be anywhere from 30-50% of the pie, whereas, for recreational athletes, the contribution of calories burned during exercise on total daily energy expenditure might be closer to 15-25%.
The most accurate way to estimate the calories burned during exercise is to wear a heart rate monitor.
#3: Physical Activities of Daily Living
In addition to the number of calories you burn during planned workouts, you also burn calories throughout the day in what is termed non-exercise activity thermogenesis, or NEAT.
Recall that BMR is merely the number of calories you burn per day resting completely stationary in a bed for the entire day.
It takes additional energy, and thus burns calories, to get out of bed and do all of the various activities of daily living like preparing meals, basic hygiene, going to work, walking the dog, taking care of your children, etc.
When determining your TDEE, NEAT is essentially a measure of the calories you burn while doing any physical activity other than deliberate exercise.
The more movement you make throughout the day, including standing, walking, carrying things, etc., the higher your NEAT will be.
Different TDEEs use various “activity multipliers” to estimate your daily NEAT caloric expenditure.
When you use the Mifflin-St Jeor equation to estimate your BMR, you can multiply the value by the following scale factors for physical activity levels:
- Sedentary = RMR x 1.2
- Lightly active = RMR x 1.375
- Moderately active = RMR x 1.55
- Active = RMR x 1.725
- Very active = RMR x 1.9
For example, someone who sits at a desk all day for work and does some light housework might multiply their BMR by 1.375 to account for their daily physical activity, whereas someone who works on their feet all day, such as a construction worker, might multiply their BMR by 1.9.
#4: Diet-Induced Thermogenesis
The remaining factor that affects how many calories you burn in a day, diet-induced thermogenesis, also called the thermic effect of food, refers to the number of calories you burn per day digesting your food.
Dietary-induced thermogenesis typically constitutes about 5 to 15% of your daily caloric expenditure, depending on what you eat.
Evidence suggests that diets high in protein and alcohol increase diet-induced thermogenesis, whereas diets high in fat have the opposite effect. This is because it takes more energy to break down certain nutrients.
For example, if you eat 100 calories of protein, 25-30 calories are burned right away just by digesting the food, leaving a net caloric gain of only 70-75 calories from that food.
In contrast, the thermic effect of carbohydrates is 6–8%, and that of fat is 2–3%.
It’s not really possible to calculate the calories burned from dietary-induced thermogenesis, so estimating a couple of hundred calories usually suffices.
Once you have an estimation of each of the four components of your total daily energy expenditure, you can add them together.
You can then use your TDEE to determine your daily caloric needs.
Remember, if you want to lose weight, you need to consume fewer calories than your TDEE; if you want to maintain your weight, you should consume the same number of calories as your TDEE; and if you want to gain weight, you need to eat more calories than your total daily energy expenditure.
Looking for some diet options? Check out our great guides on different diets to find the right one for you: The Golo Diet, The Protein Fat Efficient Diet, Intermittent Fasting, and Popular Diets For Runners.