The truth about Calories in vs calories out

A calorie deficit, in real-life language, is basically eating fewer calories than what you burn. Simple and easy when put this way, but definitely a topic that is often misunderstood because it is actually a lot more complex than that.

It also creates a lot of confusion because if the secret to losing weight is simply “eating less,” you may think that the key is fasting for a week and running a marathon a day, when in reality it is the complete opposite of what you should do when aiming for sustainable and definite weight loss. And this is why this post is so important. Understanding a calorie deficit, knowing how to apply it to your life, and knowing why some recommendations are out there and make sense (and why some are complete BS) is the key for you to take control of your fitness journey.

You’ve probably heard of calories in vs. calories out, which is the base of a calorie deficit. But how do we know what calories are out and what’s coming in? Your calories in are basically anything you eat or drink throughout the day other than water or water-like drinks (such as black coffee and tea). Probably no surprise here. But the magic happens when you know that calories out is actually a combination of four different things: your basal metabolic rate (BMR), the thermic effect of food (TEF), and physical activity, divided into exercise and non-exercise activity thermogenesis (NEAT).

Your BMR is the amount of calories you burn at rest. It’s the minimum number of calories your body requires to perform essential, life-sustaining functions such as breathing, circulation, and cell production while at complete rest. It represents about 60–70% of your daily calories burned and is influenced by age, gender, muscle mass, and genetics.

TEF is a fancy description for the energy our body uses to digest, absorb, and metabolize food. It usually represents about 10% of total daily energy expenditure. Different macronutrients have different thermic effects, meaning some foods require more energy to digest than others.

Both BMR and TEF are independent of your movement level or what you do on a day-to-day basis. Physical activity, on the other hand, is the portion of the equation we can control. This includes structured exercise as well as your everyday movement (NEAT), things like walking, standing, cleaning, and general activity. Physical activity usually accounts for about 15–30% of daily calorie burn, with NEAT making up the largest portion of that.

So now that you know all the parts of the equation, we can say that in order to lose weight you have to ingest fewer calories (calories in) than the amount you burn to survive (BMR), digest food (TEF), and move (exercise + NEAT). On paper, that sounds simple. So why are you not losing weight just by counting calories? That’s where the truth about calories in vs. calories out comes into play.

The only way to lose weight is through a calorie deficit. There’s no magic diet, supplement, or shortcut that overrides that fact. However, viewing weight loss strictly through the lens of calories in vs. calories out is an oversimplification. It usually gives you the impression that eating anything, as long as you’re eating fewer calories, will be a sustainable way to change your body, which is not necessarily true.

This approach doesn’t fully account for hormones, stress, sleep, and (mostly important) diet quality. All of these factors heavily influence metabolism, hunger, energy levels, and adherence. This is why counting every calorie while eating mostly fast food, sleeping poorly, and living under constant stress probably didn’t give you the results you expected in the past.

Food quality matters. Habits matter. Your mental and physical well-being matters. Trying to reduce all of this and the human body to a single equation that fits every person in the world is not only unfair, it’s impossible.

Weight loss and body transformation, in general, are beautiful and complex processes that can definitely be made simple and real-life-friendly, but can never be oversimplified. You deserve more than just numbers on a screen going down (although those are also part of the process). You deserve (and need) to look at yourself and your journey as a real-life combination of thoughts, realities, schedules, food choices, and all the complexities that make you human and must be taken into consideration when you’re aiming for long-term change.

Because real results come from understanding your body, not fighting it :)