The Nuance of Calories In, Calories Out; in Layman’s Terms
The law of energy balance (calories in, calories out) dictates whether we experience gains or losses in weight.
Despite this, the advice of “eating less, moving more” has failed everyone it’s been given to.
One reason for this is that the energy balance model is far more complex and nuanced than people realize.
In this article, I hope to explain some of those nuances in simple terms.
It seems to me that the lack of this understanding can lead to a sense of hopelessness surrounding weight loss or gain; something I hope to help you avoid in this article.
The basics of the energy balance model of obesity
First and foremost, any model explaining the rising rates of obesity must satisfy the law of conservation of energy, or energy balance. This states that energy cannot be created nor destroyed, and that the total amount of energy within the universe is constant.
This is the first laws of thermodynamics.
Calories are a unit of measurement for energy, the same way inches are a unit of measurement for distance. Each day, your body will burn a certain number of calories and you will consume a certain number of calories through food.
If the number of calories your body burns in a day is less than what you consume, you will have a net gain weight.
If the number of calories your body burns in a day is more than what you consume, you will have a net loss in weight.
If the number of calories burned & consumed are equal, your weight will be maintained.
The energy balance model of obesity is different from the physical law of energy balance.
It postulates that the primary cause of the rising rates of obesity are due to a significant change in the food environment.
Specifically, a drastic increase in foods that are cheap, highly-accessible, high in carbs & fat, and low in protein & fiber.
This makes it very easy over-consume calories.
In ancient times, this would be highly advantageous.
If you don’t know where your next meal is coming from, often the case with hunter-gatherers, then you would treasure such foods. By providing tons of calories with very little feelings of fullness, you buy yourself a longer period of time until you find your next meal.
As a result, we have largely evolved to like foods of this sort very much.
However, this is no longer the case. Not knowing where your next meal will come from is rarer than ever.
So, in other words, we have brains designed to value such foods and we are now surrounded by them.
Think about it this way…
If you gave your dog unlimited access to what’s in the cabinet and in the fridge, then you’d probably expect it to gain weight pretty quickly. .
Well, that’s exactly what has happened to humans.
Factors affecting “calories out”
When people hear “calories in, calories out” the first thing many think is just calories eaten and how much you move.
The truth is that it is far more complex and convoluted; much more than people realize.
Calories out refers to all the calories your body burns carrying out its functions.
More specifically, it is often grouped into the following categories:
Resting energy expenditure (REE)
Non-Exercise Activity Thermogenesis (NEAT)
Exercise
Resting energy expenditure (REE)
This categorizes the largest contribution to how many calories you burn each day.
Your resting energy expenditure encompasses all internal, involuntary activities that are calorie consuming.
Examples include your heart beating, breathing, kidney filtration, digesting food, recovering from exercise, etc.
Within your resting energy expenditure, your organs provide the largest contribution.
The energy cost of some notable organs are as follows:
Liver: ~200 calories per kilogram per day
Brain: ~240 calories per kilogram per day
Heart & kidneys: ~440 calories per kilogram per day
Skeletal muscle: 13 calories per kilogram per day
Body fat: 4.5 calories per kilogram per day
The thermic effect of food refers to the increased rate of calorie burning after a meal; the energy cost of digestion. It’s often expressed as the percent of calories from the meal that will be used in the digestion of the meal.
The dietary composition of a meal can influence the effect. Specifically, the macronutrient composition. The three macronutrients are protein, carbohydrates, and fats.
Fats have a thermic effect of ~0-3%. Carbohydrates have a thermic effect of ~5-10%. Protein has a thermic effect of ~20-30%.
Another under appreciated aspect of this includes the energy lost in stool (poop).
On average, people lose about ~3% of the energy they take in to the toilet.
Non-Exercise Activity Thermogenesis (NEAT)
This is a fancy way to say all physical movement that isn’t done intentionally as exercise.
Examples of this includes bouncing your leg at your desk, moving my fingers as I type this article, walking from your car to the grocery store, etc.
As I finished typing that sentence, I laid back in my chair and stretched my arms. I did not consciously think to do it and solely acted on impulse. That is also NEAT.
The key is that this component is unintentional. Once it becomes intentional, it is no longer NEAT.
For instance, picking first parking spot you see in the parking lot and walking in is NEAT. Picking the farthest parking spot away so you have a longer walk is not NEAT.
This provides up the second largest contribution of calories burned behind REE.
Exercise
This categorizes not just all structured exercise you do, but any movement that is done intentionally for the sake of movement.
So, not only does this include strength training, running, or pickle-ball; but it also includes choosing to take the stairs instead of the elevator.
This is the only aspect of the “calories out” side of the equation that you have conscious control over.
Factors affecting “calories in”
The substance that provides us with calories is food and beverage. Specifically, the macronutrients within food.
Protein contains 4 calories per gram
Carbohydrates contain 4 calories per gram
Fats contain 9 calories per gram
Alcohol contains 7 calories per gram
At face value, this seems simple enough.
However, beneath the surface there exists numerous complex cascades of neural and hormonal events that influence how much or how little you consume.
There is a strong gut-brain connection. If your body doesn’t feel satisfied with the amount of food it has had based on its current appetite/satiation, it will begin to pull many different levers to motivate you to eat.
Some of these include singular focus on food, irritability, etc. In other instances, it will give you a sense of fatigue; causing you to expend less energy.
Even in the context of low appetite and high satiation, being around hyper-palatable foods can increase desire for them.
Remember, our brains primarily want us to avoid starvation. It is for this reason that we have evolved to like foods that are so high in calorie for such low food-volume.
With the current food environment and advancements in food science, this problem is only growing.
Inter-individual variance
One of the most important things to note about calories in, calories out is that there is an extreme degree of variance person to person.
On the calories out side, there are a few factors that provide variability.
The most notable is organ size. Some people have bigger organs, others have smaller.
Remember, organ functions provide the largest contribution to energy expenditure in a day.
This alone can result in a difference of up to 800 calories burned per day between two people with differing organ sizes.
Similarly, I mentioned earlier than we lose some energy to stool.
I also mentioned that the average energy loss is ~3% here.
In reality, people range from ~1-5%.
After eating a meal, some people become more fatigued and others become more restless.
In other words, if two office workers eat lunch and then go back to their desks, one of them will become more still while the other might find themself bouncing their leg.
There also tends to be great variance on the calories in side as well.
Most notably, people have widely varying reward centers in their brain when it comes to food.
Some people have such a high sense of reward from food that they can’t stop thinking about food all throughout the day. This is most commonly called “food noise.”
On the flip side, other people have less of a sense of reward from food and find eating to be a chore.
In other words, you’ll never hear a person who struggles with food noise say that they “forgot to eat,” while you may commonly hear this said from someone with a low sense of reward from food.
Conclusion
The main point I sought to make with this article is this:
their are hundreds of factors influencing both “calories in” and “calories out.”
Furthermore, there’s a large degree of variance on both sides of the equation person to person.
I tried to cover some of the most notable of these features, but in truth this article only scratches the surface.
When you understand this nuance, or at least that this nuance exists, you’ll be less likely to fall for the weight loss scams so prevalent across social media.
References
Ravn AM, Gregersen NT, Christensen R, Rasmussen LG, Hels O, Belza A, Raben A, Larsen TM, Toubro S, Astrup A. Thermic effect of a meal and appetite in adults: an individual participant data meta-analysis of meal-test trials. Food Nutr Res. 2013 Dec 23;57. doi: 10.3402/fnr.v57i0.19676. PMID: 24376394; PMCID: PMC3873760.
Wang Z, Ying Z, Bosy-Westphal A, Zhang J, Schautz B, Later W, Heymsfield SB, Müller MJ. Specific metabolic rates of major organs and tissues across adulthood: evaluation by mechanistic model of resting energy expenditure. Am J Clin Nutr. 2010 Dec;92(6):1369-77. doi: 10.3945/ajcn.2010.29885. Epub 2010 Oct 20. PMID: 20962155; PMCID: PMC2980962.
Hall KD, Farooqi IS, Friedman JM, Klein S, Loos RJF, Mangelsdorf DJ, O'Rahilly S, Ravussin E, Redman LM, Ryan DH, Speakman JR, Tobias DK. The energy balance model of obesity: beyond calories in, calories out. Am J Clin Nutr. 2022 May 1;115(5):1243-1254. doi: 10.1093/ajcn/nqac031. PMID: 35134825; PMCID: PMC9071483.
Leaf A, Antonio J. The Effects of Overfeeding on Body Composition: The Role of Macronutrient Composition - A Narrative Review. Int J Exerc Sci. 2017 Dec 1;10(8):1275-1296. PMID: 29399253; PMCID: PMC5786199.
Murphy JL, Wootton SA, Bond SA, Jackson AA. Energy content of stools in normal healthy controls and patients with cystic fibrosis. Arch Dis Child. 1991 Apr;66(4):495-500. doi: 10.1136/adc.66.4.495. PMID: 2031608; PMCID: PMC1793018.
