Weight loss is determined by calories, yet some people claim they eat less but don’t lose weight. What’s going on? Do calories matter? When considering all the mechanisms and factors of losing weight, it’s obviously a complicated process.
However, saying “calories don’t matter” is a misunderstanding of how the body actually works. That is, your body doesn’t burn calories. Not literally, at least. Calories are just the measurement of energy, not the thing your body actually uses.
In fact, your body runs on ATP, and this distinction is important. This article breaks down what calories really are, how they relate to fat loss, and what’s actually happening under the hood.
Key Points You Need To Know!
The foundation of weight loss rests on how many calories we eat vs how many calories we burn.
Our bodies don’t actually “burn calories” as calories are a unit of measurement for energy.
“Energy” exists in several forms. Energy from food (calories) must be converted into usable energy, ATP.
Losing weight is complex and involves a lot of different processes. However, this doesn’t negate that it depends on balancing energy consumption and expenditure.
Weight loss comes down to balancing energy intake and ATP demand.
How Do We Lose Weight?
Weight loss is largely governed by the relationship of calories consumed vs. calories expended.
Calories consumed are relatively simple and determined by our diet.
When it comes to calories expended, here are several components that contribute to your overall Total Daily Energy Expenditure, or TDEE.
Basal Metabolic Rate (BMR)- the calories your body needs to perform basic functions at rest
Thermic Effect of Food (TEF)- the energy your body uses to digest, absorb, and metabolize food
Non-Exercise Activity Thermogenesis (NEAT)- energy used from activity not related to exercise, i.e., walking, typing, cooking dinner
Exercise Activity Thermogenesis (EAT)- energy used during formal exercise or sport.
The concept of “Calories In, Calories Out” is not a new “gym-bro” concept. In fact, “calories” were first identified in the 1800s by Wilbur Olin Atwater, the “father of nutritional science” (Hargrove, 2006).
Later in 1914, a lady named Lulu Hunt Peters wrote the first modern diet book that created the actual practice of “counting calories,” and it worked great!
But what is a calorie really?
What Is A Calorie?
Technically known as a kilocalorie (kcal), a calorie is used in nutrition to measure the amount of energy in food. A kilocalorie (calorie) is the amount of energy required to raise the temperature of 1 kilogram of water by 1°C (Osilla & Sharma, 2022).
In the context of energy expenditure and weight loss, calories measure the transfer of energy within the body.
Calories measure how much energy food provides to your body.
Your body uses this energy to breathe, move, think, and maintain body functions.
This is a lot of energy. This means that if you burn 2,000 calories in a day, that’s enough energy to increase 2,000kg (2,000 liters) of water by 1°C.
It’s important to understand this because people can often treat “calories” as an abstract concept. They’re not. Calories measure actual energy that is powerful enough to increase the temperature of water; this is the same energy that makes you hot when you train hard!
Does The Body Burn Calories?
Calories are just a measurement of energy, not what’s really powering our bodies. So when we say a food has 200 calories, we are saying it has 200 units of energy.
This is like when we say our TV uses 100 watts an hour. The TV doesn’t actually use “watts” but rather power that is measured in watts.
Still, this energy isn’t even what the body uses, but what the body uses to create the compound that actually powers the human body.
Trust us, this nuance will make sense.
Where Do Calories Come From?
Since calories are just a measurement of energy, the real question is: where does that energy come from?
This comes from our three macronutrients;
Protein
Carbs
Fat
When we consume these nutrients, our body metabolizes them to produce ATP (we’ll get to this below) (Hargrove, 2006). During this process, energy is released, and calories refer to the measurement of this energy.
Oxidation of 1 gram of Fat → releases about 9 calories of energy
Oxidation of 1 gram of Protein → releases about 4 calories of energy
Oxidation of 1 gram of Carbs → releases about 4 calories of energy
So your body takes chemical energy (substrates, i.e., fatty acids and glucose) and converts it into usable energy (ATP).
However, this process isn’t 100% efficient, and some energy is released as “thermal energy” (heat). This is what increases your internal body temperature.
“Calories measure the total energy released when your body fully oxidizes (breaks down) protein, fat, or carbohydrates to produce ATP.”
The Role Of ATP in Weight Loss
“Weight loss is complicated!”
It’s common to hear this remark in an attempt to disprove “calories in, calories out”.
It is, and while you have probably heard about hormones such as ghrelin or insulin, you probably never hear about ATP or its role. However, it’s important to understand when talking about fat loss.
ATP stands for Adenosine Tri-Phosphate, a high-powered compound known as your body’s “energy currency“ and is what actually powers your body.
It contains three phosphates, and when energy is required, one of these phosphates breaks off. This results in released energy that is used to power every single process in the human body.
Muscle contractions
Brain activity
Eye sight
Respiration
Literally Everything
Even the production of ATP requires ATP!
Depending on the fuel source and metabolic system, this entire process occurs through several different processes.
During each step, there is an exchange of energy, and the total is then quantified in calories.
ATP is the universal energy currency of the cell, and virtually all biological work, from muscle contraction to ion transport, depends on its continuous production and turnover.
The Important Part: Energy Exists In Different Forms
We often talk about energy in the body as if it’s one thing. It’s not.
Energy exists in different forms and must be converted.
Think of solar panels. They capture energy from sunlight, but that energy has to be converted before it can actually power anything.
In the human body, the chemical energy stored in food isn’t used directly to power movement or cellular work. Instead, it’s converted into ATP, the actual usable form of energy.
What would you say if someone told you their solar-powered house still runs even when it’s cloudy? Does that mean sunlight doesn’t matter?
Of course not. A house doesn’t run on sunlight directly; it runs on electricity. So you’d assume there’s another energy source, like stored power or a backup generator.
Why? Because if there were no energy source at all, the power would shut off.
So, Why Does This Matter?
As we’ve shown, most fat loss discussions focus on the “sunlight.“ But no matter how you debate solar energy, your house still runs on electricity.
And just like your house runs on electricity, your body must continuously produce ATP to stay alive and function; this isn’t an option, and you can’t override it.
Therefore, weight loss is determined by two things;
The amount of energy we eat
The amount of ATP we use
So if you’re not eating, your body must use substrates in stored form, i.e., “fat“, to convert into ATP so it can be used. Over time, this results in weight loss.
What’s interesting is that researchers are now exploring ways to directly increase ATP demand to raise energy expenditure. One interesting method is trying to guide excess energy into ATP-demanding “futile cycles”.
A futile cycle is when your body runs two opposing metabolic processes at the same time, burning energy (ATP) but producing no useful work. It’s a built-in way to increase ATP demand, which forces the body to burn more energy.
This isn’t driven by eating less, changing macros, or “boosting metabolism“ in the way people usually think. It’s simply increasing energy demand at the cellular level and illustrates how the demand for ATP is what drives fat loss (Brownstein et al., 2022).
Final Say: Fat Loss Is Complicated, But Not Really
When people point out that fat loss is influenced by hormones, it does have a role, but it doesn’t dictate fat loss. This was true even back when Lulu Hunt Peters first popularized calorie counting.
We understand that fat loss can be complicated, as there are a lot of variables involved apart from calories:
Hormones
Genetics
Environment
But this is true for every single process in the human body. That’s what makes the human body so complex and impressive.
All of these functions involve countless processes and compounds most people have never heard of.
Building muscle
Losing muscle
Thinking
Respiration
Walking
However, we can still summarize how they work with a few clear principles.
So when people say “Calories In, Calories Out,” they’re not denying that complex processes exist. They’re also not denying individual variability.
Rather, they mean that “Calories In, Calories Out“ is the foundation of how body weight is regulated. And at the center of this process is the production and use of ATP.
What’s The Best Method To Lose Fat?
Understanding the role of ATP is important when talking about fat loss.
However, it still doesn’t change the primary method of losing weight. We believe there are several key components your overall program should use to hit your fat from different angles.
Eating a healthy diet in a caloric deficit
Be involved in a progressive resistance training program at least 2-3 times a week
Cardio training at least 2-3 times a week.
Increasing your daily activity i.e., 10,000 steps a day
Prioritizing sleep.
This is why all of our Fat Loss Programs use this variety in our overall methodology to maximize fat loss and improvements in body composition.
Bottom Line: Your body must constantly produce ATP to survive. This is done using the calories you eat. If you eat a surplus of calories, that energy is stored to produce ATP later. If you’re in a caloric deficit, your body draws from energy stored (fatty tissue) to produce ATP. There is no way around this.
References
Brownstein AJ, Veliova M, Acin-Perez R, Liesa M, Shirihai OS. ATP-consuming futile cycles as energy dissipating mechanisms to counteract obesity. Rev Endocr Metab Disord. 2022 Feb;23(1):121-131. doi: 10.1007/s11154-021-09690-w. Epub 2021 Nov 6. PMID: 34741717; PMCID: PMC8873062. https://pubmed.ncbi.nlm.nih.gov/34741717/
González-Marenco, R., et al. (2024). The effect of oral adenosine triphosphate (ATP) supplementation on anaerobic exercise in healthy resistance-trained individuals: A systematic review and meta-analysis. Sports, 12(3), 82. https://www.mdpi.com/2075-4663/12/3/82
Hargrove J. L. (2006). History of the calorie in nutrition. The Journal of nutrition, 136(12), 2957–2961. https://doi.org/10.1093/jn/136.12.2957
Mookerjee, S. A., Gerencser, A. A., Nicholls, D. G., & Brand, M. D. (2017). Quantifying intracellular rates of glycolytic and oxidative ATP production and consumption using extracellular flux measurements. Journal of Biological Chemistry, 292(17), 7189–7207. https://doi.org/10.1074/jbc.M116.774471
Osilla, E. V., & Sharma, S. (2022). Calories. In StatPearls. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK499909/
Pizzorno, J. (2014). Mitochondria—Fundamental to life and health. Integrative Medicine: A Clinician’s Journal, 13(2), 8. https://pmc.ncbi.nlm.nih.gov/articles/PMC4684129/
Rizo, J. (2022). Molecular mechanisms underlying neurotransmitter release. Annual Review of Biophysics, 51, 377–408. https://pubmed.ncbi.nlm.nih.gov/35167762/
