TDEE - The Basics
Laying the Groundwork
Before we can have a conversation about the alphabet soup that makes up Total Daily Energy Expenditure, we need to take a look at the often-maligned and misunderstood kilocalorie.
kilocalorie: the amount of energy required to raise the temperature of 1 liter (1 kilogram) of water 1º celsius, at sea level. It also represents 1,000 calories.
Its original scientific usage was as a measure of heat energy. In 1887, Chemist Wilbur Atwater was the first to use the term in relation to human nutrition. Atwater's experiments formed the foundation of modern nutrition research and education. He validated that the First Law of Thermodynamics applied to humans as well as animals.
The First Law of Thermodynamics is a version of the law of conservation of energy, adapted for thermodynamic processes, distinguishing two kinds of transfer of energy, as heat and as thermodynamic work, and relating them to a function of a body's state, called Internal energy.
The law of conservation of energy states that the total energy of an isolated system is constant; energy can be transformed from one form to another but can be neither created nor destroyed.
Atwater's research consisted basically of putting a man in a box (not unlike a solitary confinement prison cell), feeding him different foods, and measuring the amount of heat generated while he performed various activities. The box was called a respiration calorimeter and was just a bigger version of the laboratory device used to measure heat in chemical and physical reactions. Yes for all my science friends, this is a super-oversimplified description, but that's the gist of the experiment.
Counting Calories is Simple Math
The phrase 'Counting Calories' is actually cringe-worthy for many people, but it's just math. Unfortunately in modern society, we've attached so many negative labels to it that it can bring on a panic attack at the mere mention.
A cornerstone of today's nutrition science is that the three macronutrients; protein, carbohydrates, and fat, each contain a specific amount of energy per gram, in the form of Calories (now differentiated as food calories) and we have Dr. Atwood to thank for that.👏🏻 The exact numbers are rounded to the nearest whole number, Protein and Carbohydrates each contain 4 calories per gram, while Fat has 9 calories per gram. This information is helpful in understanding food labels, for instance, if a particular food has 22 grams of carbohydrates in a single serving, that means it provides 88 calories from carbohydrates. If there are two servings in the package, and you eat the whole thing, you've consumed 176 calories from carbs (even when the bold print on the nutrition label shouts "88" at you! remember that's 88 per serving) Please note that there are some "accepted tolerances" of accuracy in the nutrient numbers listed on food labels, and they are better viewed as guidelines rather than etched-in-stone fact, but more on that later.
Being calorie-aware is good. Being calorie-obsessed, not so much. My goal with the rest of this post is to give you a picture of how the calories you consume are used, in a way that I hope will make sense to the average person on the street.
Acronyms, abbreviations, and industry-specific jargon exist everywhere, when you're on the "inside" they make sense and are tossed around without a second thought, however, for those who are not part of that inner circle, they can be confusing and become a barrier to understanding. The world of nutrition science is no exception. Sometimes just spelling out what the acronym stands for, or what the abbreviation means, is enough to bring clarity, in other cases, it requires a bit of explanation.
TDEE - Total Daily Energy Expenditure
This one starts to take form when you spell it out, it is the sum total of all the energy your body uses in a 24-hour period, in common vernacular, this is the same as "total calories burned". By the way, that phrase "Calories Burned" likely came from the way calories were first measured. In the past, a device called a bomb calorimeter was used to determine the energy content of food by actually burning a sample and measuring the temperature change in the surrounding water.
So if TDEE includes ALL calories expended in a day, what are the different parts that comprise TDEE? The alphabet soup version is BMR, TEF, and PA, with PA being further divided into NEAT and EAT.
BMR Basal Metabolic Rate (or RMR)
TEF Thermic Effect of Food
PA Physical Activity
NEAT Non-Exercise Activity Thermogenesis
EAT Exercise Activity Thermogenesis (or purposeful exercise)
Basal Metabolic Rate is often used interchangeably with Resting Metabolic Rate or RMR. The biggest difference between the two is that measuring is true BMR takes sophisticated equipment in a controlled environment where RMR can be estimated using a less rigorous process. I'll use the term RMR going forward simply because it's the one associated with the easier calculation.
First, let's take a look at RMR and how we can use it to estimate our TDEE, from there we'll go back and take a look at the remaining pieces that round out TDEE.
RMR - What's it all about?
Resting Metabolic Rate represents the baseline energy requirements to keep your body's essential systems running, things like pumping blood, breathing, regulating your body temperature, growing skin, creating, and balancing hormones. Imagine waking up and just sitting on the couch all day, not doing anything at all, just staring into space, your body needs to do certain things to keep you alive, it's that energy that is your RMR. (note: you may also see this referred to as Resting Energy Expenditure or REE, the terms are used interchangeably)
The big shocker to most people is that RMR accounts for 60-75% of your TDEE, meaning your body requires a significant chunk of calories JUST to keep everything running properly.
Bear with me for a brief Science Side Trip...
Your body is a complicated machine with 11 primary systems, in the best-case scenario, those systems work together flawlessly keeping you going. The main systems of the human body are:
Circulatory system / Cardiovascular system: Circulates blood around the body via the heart, arteries, and veins, delivering oxygen and nutrients to organs and cells and carrying their waste products away. Keeps the body's temperature in a safe range.
Digestive system and Excretory system: System to absorb nutrients and remove waste via the gastrointestinal tract, including the mouth, esophagus, stomach, and intestines. Eliminates waste from the body.
Endocrine system: Influences the function of the body using hormones.
Integumentary system / Exocrine system: Skin, hair, nails, sweat, and other exocrine glands
Immune system and lymphatic system: Defends the body against pathogens that may harm the body. The system comprising a network of lymphatic vessels that carry a clear fluid called lymph.
Muscular system: Enables the body to move using muscles.
Nervous system: Collects and processes information from the senses via nerves and the brain and tells the muscles to contract to cause physical actions.
Renal system and Urinary system: The system where the kidneys filter blood to produce urine and get rid of waste.
Reproductive system: The reproductive organs required for the production of offspring.
Respiratory system: Brings air into and out of the lungs to absorb oxygen and remove carbon dioxide.
Skeletal System: Bones maintain the structure of the body and its organs.
All of these systems require energy to 'do their thing'. As I mentioned above, there are sophisticated methods to calculate the total calories required to do all this with remarkable accuracy, but they are often expensive and out of reach for the normal person, and they don't lend themselves to frequent calculations. Let's take a look at a two-step process for estimating your Total Daily Energy Expenditure.
Calculating RMR (Step 1)
There are a lot of RMR calculators on the interwebs that will prompt you to enter specific information and will return your RMR as a number of total calories. Whether you use a plug-and-play calculator or scratch out the math yourself, the most widely accepted formula for computing RMR is the Harris-Benedict Formula. The result should be considered a guidepost to gauge your energy intake as opposed to a mandate that you HAVE to consume that many calories. We're all different, bio-individuality means that there is no one-size-fits-all answer to nutrition, what works for one person won't necessarily work for another.
To put this in context, I'll share my numbers. As an almost 60-year old male, 69" tall, weighing 169 pounds, my calculated RMR is 1,597 calories, which in my head I would simply round up to an even 1,600. So on a daily basis, the minimum amount of calories I need to support my basic internal systems is 1,600 calories. As I often say, this is just to keep me breathing, blinking, thinking, and pooping.
It's important to pause here for a moment and look at the role our calculated RMR plays in predicting our Total Daily Energy Expenditure. There are still other components of TDEE that we need to examine and I'll cover them in a minute, but they are generally described as an average percentage of TDEE rather than calculated ahead of time as a discrete number of calories like RMR is.
Estimating TDEE Based on RMR and Activity Level (Step 2)
Once you have calculated your RMR, the next step is to determine your activity level and apply the multiplier to your RMR. There are five categories from Little to Extreme.
Generally, you can consider these in the terms of how much you currently exercise or the nature of your primary job. Notice that I intentionally put the term 'could' in italics, there could be a variety of circumstances that relate to one level of activity or another, these are simply guides to help you categorize your activity. For example, Little to None could mean no specific exercise and having a desk job.
Moderate could mean exercising 3 to 5 days a week or having a job that is moderately labor-intensive, perhaps involving being on your feet all day or one that requires regular lifting.
Extreme could be working out twice a day, a demanding job requiring constant physical labor and heavy lifting.
To arrive at your total Estimated TDEE, multiple the calculated RMR by the appropriate multiplier in the table. Continuing the example above where I calculated my RMR of 1,600 calories, and using the activity multiplier for Moderate Activity (1.55), my Estimated TDEE would be 2,480 calories. It's important to emphasize that calculating RMR and TDEE using these tools provides an estimate that gets you into the ballpark. There are places where you can go and have more accurate metabolic testing completed, and while it is becoming more accessible, it can still be an expensive test.
Maintenance, Weight Gain, and Weight Loss
Your Estimated TDEE is approximately the number of calories you would need to consume to maintain your current weight or your maintenance calories. Adjusting your energy intake (calorie consumption) up or down will impact your weight in the same direction. Keep in mind, this is not a tidy, direct relationship but generally speaking, staying in a calorie surplus will promote weight gain while staying in a calorie deficit will promote weight loss. So yes, calories matter.
Entire books have been written on the subject, so I'm not going to go into the finer details for specific situations, but generally speaking, creating a deficit of approximately 20% of TDEE is a good place to start if you're looking to lose weight, In my example that would mean that I would reduce my daily intake by about 500 calories and see how things went. If you're making changes, approach them like a scientist, change one thing, observe the situation or outcomes over a couple of weeks, then make necessary adjustments and repeat. Changing too many things at once muddies the waters, you might not be able to identify what's working and what's not. Also, change often takes time...don't expect to see results overnight.
I keep using the terms estimated and approximate when discussing these numbers for a reason, it's important not to get too hung up on exact numbers because there is always room for error when talking calories. For instance, the Food and Drug Administration allows for the total calorie count on a product to be up to 120% of the stated value on the nutritional food label. The protein bar that says it's 200 calories on the label, can actually be 240 calories without you knowing it, and the manufacturer is not required to change the label! So when people are "managing" their calories down to the single-digit, they are likely wasting their time and stressing out over something that has a built-in accuracy tolerance.
I am not a medical professional, and the information I've provided above is just that, information. Very high-calorie deficit diets should only be used at the direction of, and under the supervision of a qualified medical professional. Using your estimated RMR as a baseline caloric intake can give you a starting point to understanding your body's energy needs.
If your goal is something other than maintenance, realize that you should periodically re-evaluate your RMR and TDEE calculations as you progress toward your goal or if you have major changes in your daily activity because your body will constantly be adapting to the changes you make.
As I mentioned above, our bodies are simply amazing, they will always seek to find balance, we refer to this as homeostasis. Homeostasis, from the Greek words for "same" and "steady," refers to any process that living things use to actively maintain fairly stable conditions necessary for survival. If you are chronically not providing enough energy for all your systems to run at full capacity, your body will allocate resources the best it can trying to maintain equilibrium, which means some systems or functions won't get all the juice they need. The results of this "energy shortage" can be manifested in many different ways, not the least of which are difficulty concentrating, digestive problems, or lethargy.
TEF - Thermic Effect of Food
The Thermic Effect of Food or TEF is usually defined as the increase in metabolic rate after eating a meal. This is the energy that is required to consume, digest, and break down the food you eat into the varied nutrients that can be used or stored by your body. On average TEF accounts for 8-10% of your TDEE, but it's virtually impossible to determine at home and it can vary significantly from individual to individual and even from meal to meal.
There are a lot of myths floating around about TEF as people are always searching for the quick fix weight-loss method, as such, there's never a shortage of products being touted in mainstream or social media that promise to "kick start" or increase your metabolism. The reality is that your body is always striving for equilibrium, so any effect these 'miracle' herbs, spices, teas, etc. may have, is very likely going to be short-lived and won't have any lasting impact on the overall metabolic process. Don't hang your weight loss goals on the calories burned chewing through a bag of celery, just saying. 🙄
Anecdotally, when I talk with clients about energy (consumption and expenditure), their estimates of consumption are always much lower than reality and estimates of expenditure are conversely overstated. Simple facts: we think we eat less and work harder than we do.
In the context of TDEE, we can break down physical activity into two categories, things we intentionally do for exercise and everything else. The "everything else" is nicknamed NEAT for Non-Exercise Activity Thermogenesis, which means EAT is those things that fall into the Purposeful Exercise category. I expect that somewhere there is a scientist laughing because they coined the acronym EAT to refer to purposeful exercise 😂
NEAT - Non-Exercise Activity Thermogenesis
Non-Exercise Activity Thermogenesis or NEAT is like the hidden treasure in the world of energy expenditure. As mentioned, it accounts for all movement/activity that is NOT purposeful exercise, so you can do just about anything and it counts in this category! NEAT can average between 15-20% of your TDEE.
I really don't like to use broad sweeping generalizations because they obviously don't apply to everyone and they immediately put people on the defensive, but in my humble opinion, our culture of making things easier through technology and mechanization has made us lazier. It's true. Let me give you a "For Instance".
Finding the closest parking space.
This applies anywhere you go in your vehicle that requires you to park, get out, and walk to your final destination. When it comes to finding a parking space it's common to find two types of drivers; lurkers, and circlers.
The lurker is the person who just parks in the middle of the lane because they see someone leave the store and walk in their general direction. Their hope is that they will be vacating a space near where they have stopped. They are generally oblivious to the rest of the world around them.
Circlers are those that will continuously circle up and down the rows closest to the entrance waiting to snatch up one of those close-up spots.
Both of these people tend to spend more time looking or waiting for that ideal spot, than if they just would have parked in the first open parking space and walked to the entrance.
NEAT Solution: Head to the wide-open spaces further from the entrance and take advantage of the extra steps that you have to walk. This also has the advantage of being less susceptible to door dings and damage from errant shopping carts!
Use your imagination, opportunities to move more and increase NEAT are all around you.
EAT - Exercise Activity Thermogenesis (Purposeful Exercise)
On average, purposeful exercise only accounts for about 10% of TDEE. Note, I'm obviously not talking about professional athletes or those that participate in a sport competitively or fall into the ranks of the "Active Enthusiast".
For example, when I was actively involved in riding Double Centuries (200-mile single day bike rides) It would not be uncommon for me to expend well over 5,000 calories on a ride, definitely not "normal" (as my family always reminded me 😂). The reality is that nowadays, with our lifestyle choices, purposeful exercise for most people makes up a very small part of the energy we use daily.
Bottom line, you don't have to get crazy with it, but you should do some purposeful exercise weekly. There are lots of people willing to tell you specifically what type of exercise is the best, but if you're not doing anything now, just doing SOMETHING is going to be beneficial. The key to success is to find something you enjoy and will continue to do, ultimately two to three times a week. Purposeful exercise should include both cardiovascular and strength-related components.
I think the most important take-away about understanding your Total Daily Energy Expenditure is that most of the calories your body uses in a day go toward keeping your basic bodily functions working and that you don't want to sabotage your body by not providing it the basic energy it needs.