Whether your fitness goal is to improve body composition, increase athletic performance or simply feel more energized, there is one crucial aspect that must be considered above all others:
Your calorie intake compared to your calorie output.
Your calorie output is defined as your TDEE, or Total Daily Energy Expenditure. You can find multiple resources like calculators that can estimate how many calories you burn every day, but this isn’t always the most accurate way to do things. Every single person has a different genetic predisposition to how their body utilizes the fuel that is put into their bodies; one method of finding your TDEE may not work as effectively for another!
The difficult part of finding your TDEE is determining how active you are outside of your scheduled workouts. How can we know how many calories we burn through our daily activity that isn’t from a workout? The most important question to ask is: “Why do we burn these calories?” When you can answer this question, new pathways of thought that relate to your goals will open up to you.
In the following paragraphs, descriptions of where your calories are being used will be presented. Additionally, you will be able to figure out how to use the scientific method to determine your personal TDEE and cater it to your own fitness goals.
There are three primary components to your daily calorie expenditure:
• Basal Metabolic Rate (BMR)
• Calories burned through activity
• The thermic effect of food
Basal Metabolic Rate
To start, lets look at a quick definition of “metabolism”. We hear this word all of the time, and it is defined as “the chemical processes that occur within a living organism in order to maintain life”. In other words, your BMR is the minimum number of calories you ought to be consuming in order for your body to work the way it’s intended to. When you consume and digest carbohydrates, fats and proteins, these molecules are then used to generate cellular energy, which will allow your organs to function at their optimal level.
Our bodies were built to have our best interest in mind; everything runs “in the background” to maintain the functions necessary for life. Skeletal muscles around the ribcage contract on their own to expand our chest so we can breathe, smooth muscle moves our consumed food through our digestive tract for absorption and cardiac muscle pumps our heart so blood can carry oxygen to areas that need it. All of these physiological processes that are required for life require energy. That is where your BMR comes in!
The majority of the calories you burn every day come from your BMR. Your BMR can be changed and it is typically changed through exercise. As you increase the amount of muscle mass your frame carries, you increase your BMR. Why? More muscle mass = more metabolic activity! Therefore, resistance training is crucial to improving your fitness level and overall health.
In the realm of fat loss, many make the mistake of not considering their BMR when they decide to cut calories out of their diet. As you likely know, glucose is the primary source of energy for our bodies. When we eat below our BMR, our bodies fight to stay alive by pulling stored fat in adipose tissue and stored glucose in muscle and the liver. The body can only carry approximately 2,000 calories of stored glucose on average, while fat stores are theoretically an infinite amount of energy because you would starve to death before your body uses all of your stored fat for energy. But remember, the body naturally craves glucose. This is why it is imperative that you do not eat below your BMR, and this is due to a physiological phenomenon called “gluconeogenesis”. This process occurs in the liver and kidneys and what occurs is a breakdown of your muscle mass into their smallest units called amino acids. These free amino acids combine with two molecules called glycerol and pyruvate to generate glucose. When we starve our body of the calories it needs to function properly, we lose muscle mass. This means our BMR decreases, and this is the last thing we want when we are trying to be healthier because it means storing fat from over-eating becomes more likely!
Now that you understand the importance of BMR, here is how you can calculate it. The quickest, but less accurate way to determine your BMR is to use the Mifflin-St. Jeor formula, which is linked right here: https://www.calculator.net/calorie-calculator.html
Have your height, weight, age and gender at the ready for this equation. Once you find your BMR, you can multiply it by a factor based on your activity to get a rough estimate of your TDEE. These factors range from 1-2 and it is based on how often you exercise per week. They are given to you with descriptions on the above website. If your goal is to lose fat, you must eat fewer calories compared to your TDEE. The opposite is true if you wish to gain weight.
A time consuming, but more precise way you can find this out is to go into a testing facility where they can use equipment to find out what your personal BMR is. Depending on your level of muscle mass, you may have a higher or lower BMR than what the Mifflin-St. Jeor equation predicts!
Calories Burned Through Activity
The next component of your TDEE is calories burned through activity. This is mainly dependent on locomotion, or how much you move your body throughout the day. This is because as you contract skeletal muscle, your heart rate increases because there is a higher demand for oxygen at the contracting muscles. When your heart rate increases, this means there is a higher demand for your metabolism to be active!
There are 168 hours in a week, and if you get 8 hours of sleep every night like you should, you have 112 hours to be active. You may exercise for 1 hour, 5 days a week, which leaves you with about 107 hours of opportunity to be active outside of the gym. I implore you to make an honest appraisal of what you do during those 107 hours. Are you sitting for the majority of those hours, or are you up on your feet?
This is where things can get tricky. Two people with the exact same height, weight, age, gender and body fat percentages can have two different TDEEs if their daily lives consist of different levels of locomotion. Comparing an accountant who sits in front of a computer during their workday versus a construction worker is a great example. I believe it is crucial that if you want to track your activity in the most accurate way, you purchase some kind of fitness tracker that monitors your heart rate. These trackers can tell you how many calories you’re burning through activity based on how your heart rate changes during the day. If a fitness tracker is out of your budget, there is a way around it. You must first consider your goal. Let’s use fat loss as an example.
First, use the calculator mentioned above to determine your BMR and TDEE. Next, subtract 500 calories from the TDEE and that number will be how many calories you should eat in a day to expect some level of fat loss. Finally, stick to that number of calories per day for a month and re-measure your body fat percentage and total weight loss. If you’re not losing fat, you’re eating too many calories! If you’re losing more than 2 lbs per week, you’re eating too little!
The Thermic Effect of Food
Remember, our bodies work to keep us alive. In the case of digestion, our digestive tract requires energy to digest, absorb and store the food that we eat. In general, you can assume that you will burn off 5-10% of the calories you eat from fat and carbohydrates simply through digestion. In other words, if you eat a 1000-calories of fat or carbohydrates, about 50 to 100 calories will be burned through digestion. Overall, protein has the highest thermic effect at approximately 25%. If you have 200 calories of chicken, roughly 50 calories will be used to digest it. Keep in mind that the calories burned or not burned from the thermic effect will not make or break you achieving your goals, but there are ways to understand why certain foods are more conducive to weight gain or loss.
In simple terms, the thermic effect of food can be slightly increased or decreased based on the kind of food you eat. When it comes to carbohydrates, the complexity of the carbohydrates you eat will have different effects. For example, a 12 oz soda that has 140 calories has a lower thermic effect because the simple sugars within the liquid can be digested very rapidly, thus less energy is required to digest it. If you were to eat 140 calories of sweet potatoes, the long chains of starch within the potato mixed with fiber require far more energy to break down and digest. Therefore, your body must increase its metabolic rate within the digestive system to make sure it is properly digested and absorbed, which means more calories burned!
A diet rich in complex carbohydrates, unsaturated fats, fiber and protein will be the most thermic diet one can have!
Lets put this whole process into action with an example. After you read this, do it for yourself!
First, we have a subject named Carl. He is a male that is 25 years old, 5’10”, and 215 lbs with 30% body fat. His goal is to burn off fat and get down to 180 lbs. He is also expecting to exercise 5 times per week, however he has a very sedentary job and doesn’t get much activity outside of the gym.
Carl’s first step is to determine his BMR, and he uses the Mifflin-St. Jeor equation to find out that he burns approximately 1969 calories per day in order to stay alive. If he sticks to his goal of exercising 5 days per week, he can multiply his BMR by a factor of 1.55 to get a TDEE of 3051 calories per day. We assume that this is his TDEE because he does not get any activity outside of his scheduled workouts, however there is a possibility that it is a few hundred calories more when he’s walking around work or around his home. Since his goal is to burn off fat, he needs to eat 500 calories less than 3051 calories, which is 2551 calories.
His diet consists of whole grains, plenty of lean protein, fibrous vegetables and unsaturated fat. Therefore, the thermic effect of the food he eats will burn more calories than if he were eating mostly refined grains, sugar, low protein and low fiber.
Now lets imagine that he sticks to 2551 calories per day for an entire month and he exercises 5 days per week. He then checks his progress at the end of the month by weighing in and measuring his body fat percentage. His body fat percentage went down by 2% and his weight dropped 5 lbs over 4 weeks. At a rate of about 1 lb. lost per week with a drop in body fat percentage, it becomes clear to him that this is very sustainable over time! If he were to see no changes at all, or even an increase in body fat and weight, 2551 calories is too high! He will then have to re-evaluate how many calories he consumes every day and check again after the next month passes.
In essence, Carl is using the scientific method to determine how many calories his body needs to lose the fat he wants to lose. The calculations he did in the initial stages are his hypothesis. He speculates that if he eats 2551 calories per day and exercises 5 days per week, weight loss will occur. When he weighs in and checks his body fat percentage, he is collecting data. After he analyses his data and it shows him fat loss, then he does not need to change his approach. If he were to gain fat, he would have to formulate a new hypothesis. If this were to happen, the last thing Carl should do is become discouraged and stop trying to achieve his goal, because small tweaks to his plan can always be made!
• Your BMR is the minimum number of calories your body needs to stay alive and is the majority of the calories you burn every day. It can be calculated through equations or directly through medical equipment.
• The calories you burn through activity can be difficult to measure directly if you do not wear a fitness tracker. Thus, using the scientific method to figure out your activity level by determining if you are on the right path to achieving your goal can be a very beneficial practice.
• While it is a small effect, you can increase the thermic effect of food by consuming foods that require more energy do digest, absorb and store.
I hope all of this information can help you achieve your goals by the end of this year, or even sooner!
NSCA Certified Personal Trainer, BS Exercise Science, NCCPT Certified Weight Management Specialist