This article is probably going to be more technical than practical, but I had to make my version of it and leave it for those who want to delve a bit deeper with their curiosity as to what energy means in our body, at least in terms of how we calculate it for applicable purposes.

In nutrition when we talk about the result of food consumption and energy expenditure to measure out some change in body composition, Energy Balance is at the core of our reasoning.

We have two factors that define Energy Balance: Energy In and Energy Out. In this article I want to discuss more thoroughly where does the calculation used to estimate the Energy out in the equation comes from.

This is known as Total Daily Energy Expenditure (TDEE), and is usually divided into 4 components: Basal Metabolic Rate (BMR), Thermic Effect of Activity (TEA), Thermic Effect of Food (TEF), and something known as Spontaneous Activity (SA) that we cannot include in our estimate, and the reason will be discussed towards the end. So we have:

BMR + TEA + TEE = TDEE

Ok I know it’s a lot of abbreviations, and each component you might have read it differently somewhere else, but these are the terms that I’m going to define. Richard Feynman never worried to learn the name of something, but rather how it works and what it means, so with that mentality we shall define them.

Basal Metabolic Rate (BMR) 

In the majority of the population this is the factor that constitutes the highest percentage of the TDEE. It refers to the amount of energy that is required to meet the body’s basic metabolic functions, simply by existing we spend calories because there is an energy cost to keep us alive.

Our weight is the biggest determinant to calculate this number, however it should be mentioned that there are differences in genetics, body composition, gender, and age that may alter this value, but in reality these variations are small. In any case the only thing we can change is our weight and body composition.

Having less fat and more muscle always helps to improve our calorie expenditure in this respect, as well as affect other components as we’ll see later, and this happens due to the fact that muscle tissue is more active than fat tissue. I want to mention that it is not an astronomical difference as some people think, but it’s something appreciable.

So, in a practical sense we know that we cannot affect our genetics, gender or age, but we can change our body composition to improve this element. In any case our weight remains as the most important to estimate BMR.

There are several methods to do such estimation, the Harris-Benedict formula for example uses your height, weight and age to estimate your BMR and is usually not as accurate, and the Katch-McArdle formula uses lean weight, for which you must know your body fat and is the most widely used for its precision. It is a good idea that you use both for testing, but if you have to use one I recommend the Katch-McArdle, the Harris-Benedict tends to overestimate for not taking into consideration lean bodyweight.

However, I have a simple and fairly accurate method to use for an estimation: multiply your weight in kilograms by 22 (weight in pounds by 10). Someone who weighs 80kg would then have a 1760Kcal BMR.

Thermic effect of activity

Any activity we perform actually goes in this component. From moving your arm to reach your smartphone to the formal exercises in the gym. As you can imagine, this factor is the most variable, an athlete training 4 hours a day burns considerably more calories than an office worker.

Fortunately, there is a good reference with a multiple we can use depending on which category we feel we belong to, based on our lifestyle and physical activity.

• Sedentary (little to no exercise): BMR x 1.2
• Lightly active (exercise or sports 2-3 days a week): BMR x 1.35
• Moderately active (exercise or sports 4-5 days a week): BMR x 1.55
• Very active (exercise or sports 6-7 days a week): BMR x 1,725
• Extremely active (exercise, sports and vigorous work daily): BMR x 1.9

This is a good time to clarify the reality of caloric expenditure with formal exercise. Contrary to what people tend to think, cardio exercises do not burn as much as it is speculated. This will vary depending on the weight, intensity and duration of the session, but on average a cardio session can burn about 300-400 calories per hour, in many cases less.

It is still an appreciable amount and is an important tool to create a caloric deficit, the problem arises when there is a disconnect between the calories consumed and burned. There are people who feel the need for a sports drink after a hard cardio session, a single bottle can have 200 calories or more. A simple decision like that can completely override the efforts of one hour with the idea in mind of burning extra calories.

Lifting weights doesn’t have a great impact either in calories burned during the session, perhaps the greatest effect is in the following days where the metabolic process of reconstructing and synthesizing muscles occur. In any case, the calories burned are lower than you think.

Having said this, the multipliers in the table above are a good way to estimate the TEA. Continuing with our 80kg person, and assigning him a light activity of exercises 2-3 days a week we would have:

1760 x 1.35 = 2376Kcal.

Thermic effect of food

Digesting what we eat takes energy, since it has to be processed in different ways and by different mechanisms. The required amount depends on each macronutrient as we’ll see.

• Fats are those that require less processing, it is estimated that only 3% or less of calories consumed as fat is used to process them.
• Carbohydrates take more energy to be processed, around 6% of the calories coming from carbohydrates are used.

• Proteins are the ones that require more calories to be processed, 25% or more on average of the calories consumed in proteins are used to digest and metabolize them.
• Alcohol… I would feel empty if I don’t include the fourth macronutrient and its thermic effect. It takes about 20% of their calories to be processed.

In any case these percentages are for nerds like me who want to play with numbers, but it’s impractical to calculate daily this component. However, for the purposes of providing a general number to use, 10% of the calories consumed tend to be lost in digestion.

Continuing with our 80Kg guy, consuming 2400Kcal daily we would have 10% as:

2400 / 10 = 240

Then 2376 + 240 = 2616Kcal is your estimate. And please, for the love of god round your numbers to the nearest zero.

Here is where the estimation of 33Kcal per kilogram (15Kcal per pound) for someone who trains 2-3 times a day comes from.

Spontaneous activity

Finally, we have this component that we can’t include in our calculations because of the nature of its effects and individuality. You may have also heard about it as Non Exercise Activity Thermogenesis, or the cute acronym NEAT.

Basically this refers to the unconscious movements that serve no apparent purpose, and may create a huge difference in caloric expenditure.

We all had that skinny classmate that wouldn’t stop moving in his chair and used to move fast. These people have this intrinsic drive to walk fast and fidget a lot in general.

Now the problem with calculating this variable is that 2 people may vary up to 1000Kcal per day due to this. To some extent we all have a level of NEAT, and it’s no surprise that the more obese the person is, the lower his NEAT will be. Another factor affecting it is prolonged caloric deficits, that lethargy that we experience during diets makes us move less and more slowly, effectively reducing our energy expenditure through NEAT.

When we overconsume calories over a prolonged period of time generally the opposite happens and we tend to move more, but then again this is completely individual and the magnitude can be very low to very high. Unfortunately it seems that the people who have the highest response in NEAT due to over-consumption are those that naturally have it high already, which further aggravates their goals of weight gain.

Now even though this factor is not something that we can estimate in our calculation, it serves to remind us at this point that all this is just an estimate based on the best information that we have, the individuality of each one of us will determine the true value of our energy expenditures, and the only way to measure that number is properly monitoring of our energy balance.

Conclusion

We have 4 components that determine our Total Daily Energy Expenditure (BMR, TEA, TEF, and NEAT), 3 of them serve to make a good estimate, and the fourth reminds us that monitoring the progress of a diet is what will tell us exactly how much we are spending daily.

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Thanks for reading, questions are always welcomed in the comments.

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