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  • Writer's pictureDarshini Krishna

The Science Behind Weight Loss

Updated: Jul 28, 2022

How Does Weight Loss Work Scientifically?
How Does Weight Loss Work Scientifically?

There is TOO MUCH information and misinformation out on the internet on what causes weight loss and gain.

And while not everything is wrong, the fundamental gap in people’s understanding comes in the science of weight loss.

Without fully understanding the science behind why you lost weight in the first place, you will not be able to sustain that result in the long-term.

This will will lead to you jumping between fad diets while you watch your weight yo-yo- not ideal.

Obsession without a base understanding of science is unhealthy

Have you ever wondered why some people can eat sugar and junk food regularly and still stay thin?

Have you ever wondered why you seem to be “doing everything right” and still find it difficult to shed pounds?

Well, the principle of energy balance answers this question.

Let’s dive in.

When it comes to changes in weight (weight loss and weight gain), energy balance is key.

What is Energy balance?

Energy balance is the balance between calories in vs calories out.

Very simply, a negative energy balance leads to weight loss, whereas a positive energy balance leads to weight gain.

If Calories In > Calories Out: You will gain weight

If Calories In = Calories Out: You will maintain weight

If Calories In < Calories Out: You will lose weight

On the “Calories in” side of the equation, it is simply the total amount of calories you consume everyday.

You get this from adding up the calories contained in all the foods you eat throughout the day.

Whereas the “Calories out” side of the equation is more complicated, and consists of 4 main components.

The 4 Basic components of “Calories out” is also known collectively as “Total Daily Energy Expenditure” (TDEE).

1. Basal Metabolic Rate (BMR)

The biggest component of your TDEE, BMR accounts for approximately 60-70% of TDEE.

If your maintenance calories are 2300, BMR constitutes 1380 kcal.

This is the amount of energy your body needs just to exist and perform basic bodily functions like breathing, keeping your heart pumping, organs working. You get it.

Think even if you lie in your bed the whole day doing nothing, you would burn at least this amount of energy just existing.

How Weight Loss Works

2. Non-Exercise Activity Thermogenesis (NEAT)

NEAT is the amount of energy you spend doing unconscious little movements throughout the day that aren’t exercise- think fidgeting, blinking, shaking your leg, talking, walking around the house.

This is the most adaptive part of metabolism, meaning it increases significantly during a calorie surplus, and decreases significantly during a calorie deficit.

This constitutes roughly 15-20% of your TDEE.

3. Exercise activity (EA)

This refers to the amount of energy or calories you expend during intentional exercise.

This of course varies based on the type of exercise you perform and the duration and intensity at which the activity is performed at.

Energy burned through exercise actually constitutes far less on average to TDEE than people realize, at about 10%.

Which is why while training is a key factor in building muscle, it should not be the primary driver of weight loss.

4. Thermic Effect of Food (TEF)

TEF is probably the most interesting piece of TDEE, did you know that it also costs you energy to extract energy from the food you eat?

Different foods require varying amounts of energy to be digested.

The TEF for Protein is 20-30%, Carbs 5-10%, and Fats 0-3%.

To illustrate this, that means for every 100kcal of Protein you consume, you only extract 70kcal of energy from it, 30kcal gets wasted.

Whereas for every 100kcal of Fat you consume, you only dissipate about 3kcal of energy processing it, and retain 97kcal.

While this does not mean you should only eat protein, it definitely shows that not all calories are created equal

Here are the overall takeaways:

Firstly, the quantity of calories you consume matters more than the source of calories you consume.

This means that even if you ate just Macdonald’s burgers and maintained a calorie deficit, you will lose weight.

(And no, don’t do that, I’m just saying!)

In other words, it is impossible to gain weight in a calorie deficit.

If you did gain weight, then by definition you were not in a calorie deficit.

Secondly, while calories are the most important thing, not all sources of calories are created equal

Yes, I know it's confusing.

What I mean by that is that they do not all produce an equal amount of weight gain or loss, depending on macronutrient breakdown.

Thinking back to TEF explained above, the TEF for Protein is higher than that of Fat and Carbs, so even for the same calorie input, there is a difference in fat loss between diets with different macronutrient splits.

Generally speaking, higher protein intakes also have demonstrated better fat loss and lean body mass retention.

Lastly, a key thing to point out is that TDEE is not static.

What this means is that you do not burn the exact same amount of calories daily, and your metabolism is highly adaptive, meaning that there is an interconnected relationship between calories in and out- i.e. how much you consume affects how much you output.


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