Cracking the Code of Nutrition: Unlocking the Math Behind Your Diet

Why Calories, TDEE, and BMR Hold the Key to Smarter Eating and Better Health

Math is undeniably no fun, at least for me it is not. But nutrition is no fun without its math. In this article, let us talk about numbers and metrics in nutrition. Before I even delve any further, here is a list of key metrics that will be used in their abbreviated form across the article and what they stand for. 

TDEE – Total Daily Energy Expenditure

BMR – Basal Metabolic Rate

NEAT – Non-Exercise Activity Thermogenesis

REE – Resting Energy Expenditure

TEF – Thermic Effect of Feeding

EAT – Exercise Activity Thermogenesis

NREE - Non-Resting Energy Expenditure

Now that we have got that out of the way, let us dive deeper into the most talked about, most famous metric – the TDEE. 

What is TDEE?

If you have been looking into what you eat, specifically on the lines of weight loss, and/or weight gain, TDEE is something you must have come across a million times now. TDEE, as the name stands for, is simply the total number of calories that your body needs, based on your energy expenditure. In layman’s terms, energy expenditure translates to - a) your activity levels – both exercise and non-exercise activity, and b) the number of calories your body burns at rest. Knowing your TDEE helps you in many ways – a) helps you determine how many calories you need to consume daily with relative accuracy b) helps you plan your meals better to ensure you get a whole host of nutrients in, and c) helps you plan your exercise levels in tandem with your calorie intake to achieve your fitness goals.

Components of TDEE:

TDEE is made up of 4 components – BMR (which is also your REE) being the largest – 70% of your TDEE, followed by 3 NREE components – NEAT – 25% of your TDEE, TEF – 10% of your TDEE, and EAT – just about 5% of your TDEE. The fact that exercise makes up just about 5% of your TDEE can always be surprising, no matter how many times you read it. 

Basal metabolic rate (BMR) refers to the number of calories you burn to perform essential biological functions like sleeping, breathing, digestion, etc. It makes up the largest portion of your TDEE - 70 percent.

Non-exercise activity thermogenesis (NEAT) refers to calories burnt from any activity that is not exercise based, such as moving around the house, climbing that one flight of stairs to your terrace, that crazy set of moves you dance to a funky tune from the 90s, that meeting you take standing, etc. This makes up 25 percent of your TDEE.

The thermic effect of food (TEF) is the amount of calories your body burns to digest, absorb, metabolize, and assimilate the food you consume, accounting for 10 percent of your TDEE

Exercise activity thermogenesis (EAT) is the amount of calories burnt during exercise – i.e., when you are trying to break a sweat on purpose, accounting for only 5 percent of your TDEE.

Non-resting Energy Expenditure (NREE) is the total amount of calories burnt through physical activity and thermogenesis.

Keep in mind that these numbers are average figures, as they do tend to vary based on your constitution, lifestyle, food consumption, and activity levels.

How to calculate TDEE?

The easiest way to calculate TDEE is to use one of the online TDEE calculators popularly known as calorie calculators. These calculators use age, gender, height, weight, and activity level as input to calculate your TDEE. While this is an easy and quick way to determine your TDEE, most online calculators are deficient in that they tend to have the user make assumptions about body composition, not factor in muscle mass, etc. thus leading to an incorrect estimate of your TDEE. Typically, these calculators are one-step calculators and do not take BMR into account. A more accurate way of determining your TDEE is to use a TDEE formula that takes BMR into account. Again, there are several formulae that one can use to determine, but by far the most popular and accurate formulae are the Katch-McArdle equation and the Harris-Benedict equation.

Katch-McArdle Equation for BMR

The Katch-McArdle equation factors in lean body mass percentage, which is a great parameter to make your TDEE figures more accurate. However, calculating Lean Body Mass (LBM) needs an accurate measure of your body fat %, which can be acquired only with the help of a professional. Once you have your body fat %, you can plug it into the following equation to arrive at your LBM:

Lean Body Mass = (1 - (body fat/100)) x weight in kg

We then use the LBM figure in the Katch-Mcardle equation to arrive at the BMR as follows:

BMR = 370 + (9.82 x lean body mass)

Harris-Benedict Equation for BMR

On the other hand, the Harris-Benedict equation uses weight, height, and age and multiplies them by pre-determined constants to determine BMR:

BMR for men = 88.362 + (13.397 x weight in kg) + (4.799 x height in cm) - (5.677 x age in years)

BMR for women = 447.593 + (9.247 x weight in kg) + (3.098 x height in cm) - (4.330 x age in years)

Calculating TDEE

After you get your BMR, you can then multiply it by the respective physical activity factor from the table below to get your TDEE:

TDEE and The Calories-In-Calories-Out(CICO) Diet:

More often than not, those who have their TDEE calculated, venture into the popular Calories-In-Calories-Out (CICO) diet. The CICO diet is simply a dictation of how many calories you eat to lose weight. You calculate your TDEE and deduct a few calories (typically 10-15% of your TDEE) in order to introduce a calorie deficit in order to eat fewer calories than you burn. For example, if your TDEE is 2000 kcals, you eat 1800 kcals worth of food every day which will then allow your body to burn stored body fat to meet energy requirements. Sounds easy, and it definitely is a great first step to moving your body toward optimal body weight. However, eating fewer calories than needed in the long run is a no-no.  

Why CICO Doesn’t Work: 100g of Ice Cream Vs 100g of Chicken

Eating fewer calories than needed for a continued period of time slows down your metabolism. Additionally, if you have been experiencing poor appetite, staying on a calorie deficit is only going to make it worse. On a CICO diet plan, one can eat 100g of vanilla ice cream worth 207 calories or 100g of chicken worth 220 calories every single day and still stay in a calorie deficit. In fact, the ice cream does seem more lucrative simply because it has slightly fewer calories than the chicken. However, when we start breaking down the nutrients in the ice cream vs that in chicken, the chicken is a clear winner because of the plethora of nutrients in it, in comparison with the ice cream. Deprivation of nutrients for sustained periods of time can also be a leading factor in poor mental health as nutrition is heavily intertwined with human cognition, behaviour, and emotions.

Conclusion

Thus, it is safe to conclude that, while TDEE is a great tool to understand one’s daily caloric needs and use it as a guide to planning your meals more effectively, it is definitely not the sole tool that one should rely on to manage your overall health, inclusive of weight management. 

But hey, I have a question, you ask. How can my TDEE be constant? Is it not going to change as I lose or gain weight., as I age, and modify my physical lifestyle? Of course, it does. As you age, or as you lose weight and your body composition changes, your body’s basal metabolic rate changes, in addition to the thermic effect of food which is unique to one’s constitution. But my dear reader, will you please let me pique your curiosity as I tell you TDEE can also change with the change in seasons, as well as geographic regions? More on that in part 2- coming soon.