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What are Calories?

There are a lot of crazy people on the Internet.  Sometimes I have even been one of them.  But this article is about a different kind of crazy person.  I won’t name him since I don’t believe in giving crazy publicity or even acknowledging them by name but he sends myself and others in the field relentless numbers of all caps insane emails.  He’s a complete nutjob.

In the most general sense, he’s one of the deniers of energy balance and Calories In Calories Out (CICO) as it pertains to body weight and body composition.  It’s the typical bs although his newest insanity is how calories not an actual thing that exists and, by some sort of extension I guess, that the calorie model of changes in body weight is incorrect for that reason.  That is, since calories doesn’t exist, they can’t explain the changes that occur in terms of bodyweight or body fat.

Now, in one sense, this crazy person is actually correct: calories are not a thing in the sense of physically existing in this universe.   I can’t put a calorie in your hand, I can’t feed you a plate of calories per se (and that will make sense in a moment), I cannot show you a physical object that is a calorie.  I could do those things with, say, a quarter or an apple.  I can’t do it with calories.

But does that make him right about the rest of it?  Would I be writing this article if it did?

What are Calories: Part 1

This crazy person’s mistake, well one of them anyhow, is in assuming that anyone has ever claimed that a calorie is a physical object in the first place.  It’s just a weird strawman that exists only in his mind.    And that is because a calorie isn’t a physical object. Rather it’s a defined measurement.  Specifically it is a measurement of heat.

Even more specifically:

One calorie is the amount of energy required to heat one gram of water by one degree Celsius.

So let’s say you have an apparatus to do this type of experiment.  You put whatever you’re going to burn into it, burn it and measure the amount of heat given off.  Or rather you measure how many grams of water it can heat by 1 degree Celsius.

Or how many degrees C it can raise one gram of water I suppose.  So say you burn this and it raises 5 grams of water by 1 degree Celsius.  That would be defined as 5 calories.  If it raised 10 grams of water by 1 degree, that’s 10 calories.  If it raised 1 gram of water by 10 degrees, that’s 10 calories.

One calorie is the amount of energy required to raise the temperature of one gram of water by 1 degree C.

Note: In Non-America, it’s more common to use joules as a measure of heat but the concept is exactly the same. One calorie is equivalent to ~4.2 joules so if burning something raised the temperature of 1 gram of water by 1 degree Celsius, that would be 4.2 joules.  Since I’m an American, I will use calories throughout this article.  And that leads me into the next topic.

Calories vs. Kilocalories: Part 1

Before I continue, let me make what may seem like a pedantic note but one which is actually very important and which can cause major confusion.  In common parlance, people tend to use the terms calorie (cal) and kilocalorie (or kcal) somewhat interchangeably.    This is completely incorrect.

The prefix kilo means 1000 in Communist/Metric units.  Thus 1 kilocalorie is equal to 1000 calories in the same way that 1 kilogram is equal to 1000 grams.    Technically speaking, if someone said they ate 2000 calories (cal) per day and another said they ate 2000 kilocalories (kcal) per day, the second would be eating 2,000,000 calories.  And exactly nobody would assume that is true or that the terms were being used literally.

In common parlance, calories and kilocalories are used synonymously.

Scientists don’t usually make this mistake although there is an extra bit of confusion that causes some real problems.  By naming and writing convention 1 calorie (with a lower case ‘c’) truly represents 1 calories and 1 Calorie (with an upper case ‘C’) represents 1 kilocalorie.  So very very pedantically speaking:

1 Calorie (Big C) = 1 Kilocalorie (kcal) = 1000 calories (little c).

Which would be fine if people paid attention to things like capitalization (Capitalization?) which they often don’t (I am 1000% sure or is that 1 Kilo% that I don’t pay that much attention to it).  So strictly speaking someone might write that they were eating 2000 Calories (upper case C) and this is the same as eating 2000 Kcal but is not the same as eating 2000 calories (which is only 2 Calorie or 2 kcal).

Is this making sense?  I hope so because it does get confusing as all hell and this is actually a place where the common parlance is easier to follow than the scientific terminology, especially when people are careless in their writing.

Which I only bring up to

  1. Show off my knowledge of irrelevant and fairly pointless trivia (and if you want a tedious history of the topic of calories click here)
  2. Point out that the equation I presented above is for calories with a little c. rather than kilocalories.

The increase of 1 gram of water by 1 degree Celsius truly represents a single lower case calories and 1 kcal (or Calorie) would represent increasing 1000 grams of water by 1 degree Celsius (or I suppose 1 gram of water by 1000 degrees Celsius).  I’ve seriously forgotten what I’m talking about at this point.  This is just me showing off.    Practically, none of this is that important.

Calories vs. Kilocalories: Part 2

And this is only really important because, when you’re talking about diet, you are always always always talking about kilocalories (or Calories).  Always.  And this is primarily an issue of the math involved.  If anybody truly used 1 calorie (lower case ‘c’), the numbers get stupid.

As an example, the average apple contains 100 kcal (100 Calories with a big “C”) which means that it contains 100,000 calories (little “c”).  Which means that a 2000 kcal/Calorie diet would technically contain 2,000,000 calories (little “c”).    If you wanted to create a 500 kcal/big C calorie deficit, that would be written as 500,000 little c calories.  And the numbers become difficult to work with.

It would make those stupid 10,000 Calorie/Kcal food challenges on Youtube more fun to read about, though.  “Yeah, bro, I ate 10,000,000, that’s right, 10 MILLION calories today.  Come at me.”   Anyhow.

Note: In the same way that there are joules, there are also kilojoules (1000 joules) and the concept is identical although I don’t think there is the same nonsensical bs about upper and lower case letters.  Since 1 calories is equivalent to 4.2 joules, 1 kcal is the equivalent of 4.2 kilojoules and 2000 Kcal is the equivalent of 8400 Kilojoules.  Which would be all and well except sometimes studies report energy intake in megajoules which is 1000 kilojoules (which is 1,000,000 joules).

I hate this because research will report that the diet contained 4.2 megajoules which means it contained 4200 kilojoules and then you have to divide by 4.2 to get that it contains 1000 Calories/Kcal.  Some journals, realizing that Americans (including myself) by and large can’t do metric, report energy intake in kcal/kilojoules or kcal/megajoules and I like those journals a lot because I truly do suck at math and my desk is messy so I tend to lose my calculator.

Regardless of all of the above, moving forwards I will use the terms calorie and kcal interchangeably and you can assume that I mean the common usage and that they are identical.  I am usually lazy and just write calories but take this to mean kilocalories unless otherwise noted.

Calorie Bombing

So what does this have to do with food intake?  Well, while it can be defined in terms of food intake (I ate 3 apples today) or macronutrient intake (I ate 100 grams of protein, 200 grams of carbs and 50 grams of fat today), diets are also often spoken of in terms of their calorie or energy level.

It might be said that someone requires 2000 calories per day to maintain their weight or that they should eat 500 calories below energy expenditure to lose weight or 500 above to gain weight and this is the fundamental basis of the energy balance equation.  But what does this mean?

In the lab, you can put nutrients or foods in what is called a bomb calorimeter (which would be a great band name: let’s welcome to the stage Bomb Calorimeter, followed by The Thermic Effect of Food!!!!!) and burn them.  And then you measure the amount of heat given off.

And this tells you the calorie value of that nutrient or food.  Again, calorie in this sense is just a defined measure of heat (1 calorie is the heat to raise the temperature of one gram of water by 1 degree C). It’s not a thing.

Decades ago, a dude named Atwater did this for individual nutrients and derived what are called the Atwater factors.  Traditionally these are given at 4 kcal per gram of protein and carbohydrate, 9 kcal per gram of dietary fat and 7 kcal per gram of alcohol.

There’s a little bit of slop in this, not all proteins, carbohydrates or fats produce exactly that amount of heat when burned but they are all in that range on average.  So one protein might be 3.7 and another 4.3 but, meh.  Athletes are already obsessive enough without getting this far up their butt.

Which just means that the calorie values of food are nothing but a representation of the heat energy given off when they are burned.  If burning a food raises X grams of water by Y degrees Celsius, we then CALCULATE the calorie level.  Beating a dead horse, calories are not a physical entity, they are a defined and measured/measurable quantity.

Denying Bomb Calorimetry

Now, the true CICO deniers will make a few different arguments one of which is that the human body is not a bomb calorimeter.  This is correct.  Foods do vary in how they efficiently they are absorbed from the stomach and this can vary somewhat for any given food.

Fats have about a 97% efficiency of digestion, proteins vary from about 85-95% with animal proteins showing higher values than vegetable proteins and carbs can be as low as 80% due to the fiber intake.  Food not absorbed comes out the other end (trivia: this is why higher carb diets produce more poop than low-carb diets, carb foods produce more poo residue) but this isn’t ever counted.  If the food isn’t absorbed, it’s not counted in the energy balance equation.

Foods are also metabolized within the body and some of the energy may be lost in this metabolism.  This is usually called the Thermic Effect of Food (TEF), Specific Dynamic Action (SDA) or Dietary Induced Thermogenesis (DIT).  These are all slightly different things but think of them as the energy value of the food that is lost during digestion and basic metabolism before those calories are “stored” in the body.

There are other potential differences due to how nutrients may be utilized in the body.  As a random example, while dietary fat is stored with nearly 100% efficiency after digestion (and has a tiny TEF), dietary carbohydrates will lose about 23% of their energy if they are converted to fat (a process called De Novo Lipogenesis or DNL).   And this might be relevant except for the fact that the process of DNL rarely happens in humans.

And what the CICO deniers will point out is that due to these factors the Atwater values don’t hold or don’t matter.  The 4 cal/gram for protein won’t be 4 cal/gram in the body because of varying digestion/absorption, TEF, etc.

And they might be right except for this fact: these variables are already factored in to the numbers.  In a bomb calorimeter protein has a calorie value that is actually higher than 4 cal/gram.  The 4 calorie per gram value has already been adjusted for fact that the body will handle it somewhat differently than if you burn it in the lab.   So, as is mostly the case for this particular group of nimnods (yes, nimnods), it’s a non-argument based on a non-understanding of what the numbers actually represent.

A Short Diversion from Calories

Before continuing let me make a couple of points.  The first is that the above, the fact that calories are not a real physical object but simply a defined value is true of other things that we use.  During bicycle riding, we can define and measure the watts produced.  It’s a measure of power which is work over time and I won’t bore you beyond that.  Watts are not a thing I can give you, I can’t hand you a bottle of watts.  It’s a defined physical quantity that can be measured.  And nobody questions it.

And simply represents a measurement of the power produced by the act of muscles contracting.  That muscle contraction is fueled by ATP (adenosie triphosphate) and that ATP is produced by the metabolism of stored carbohydrate of fat within the muscle.  Basically watts are an external defined measurement that represents the metabolism of something real.  It’s simply a proxy for the fuel being used by the body to generate muscular force.

Quite in fact, you can put a person, exercising or not, into what amounts to a huge bomb calorimeter and measure their calorie expenditure in the same way you’d measure it by burning something: by measuring the amount of heat that they give off and determine how much that would raise the temperature of water based on the definition of a calorie.

The calorie expenditure of sitting or walking or exercising is simply a proxy for what is happening metabolically within their body.  And yes there are other ways to do this same thing such as indirect calorimetry which uses oxygen and Co2 metabolism or doubly labelled water which is too complex to get into.

The same might be said of horsepower in a car engine.  This is defined, oddly, as the amount of power produced by a single horse and this is one of those weird leftovers of a time when bushels were considered a useful measurement.  So a car might be said to produce 50 horsepower, the same amount of power that 50 draft horses put together would produce.

Of course, horsepower is not a real thing and I can’t give you a bag of horsepowers (I can give you a bag of horse poo at best).  It’s a defined quantity that ultimately represents how the engine is working based on the combustion of gasoline.  Like watts for muscular work, horsepower is simply a proxy for the combustion of a real physical object.  Horsepower may not be real but it represents the end result of utilizing something real.

Can you see where I’m going with this?

Calories as a Proxy for Nutrients and Food

Strictly speaking, saying that a food “contains” a certain number of calories is incorrect.  You couldn’t open the food or cut it into smaller pieces and remove the calories (since calories are just a defined measurement).  Strictly speaking, saying that someone “eats a diet” of 2000 calories isn’t correct since they aren’t eating calories in the sense of those calories being a physical thing.  This isn’t like eating 2000 M&M’s.

But this is just semantic stupidity, arguing about the use of the words “containing” or “eating” calories.  Which is what the crazy person’s argument amounts to: since calories aren’t a physical thing, and we can’t/don’t “eat” calories in a literal sense they don’t apply or have no relevance to talking about the body.

But those terms, are just a semantic shorthand for more complicated processes.  We eat food, which contains nutrients which when metabolized by the body generate energy which can be translated into heat which can be measured in calories.  Calories are simply a proxy for the food/nutrients in the diet.  Nothing more and nothing less.  No, they don’t exist in the sense of being a real physical object.  Rather, they are real in that they represent the end result of the metabolism of something real.

And it would be tedious to continuously say “An apple contains nutrients that, after digestion and TEF are accounted for, generates the heat energy during oxidation to raise a certain number of grams of water by a certain number of degrees C which can be calculated as 100 calories.” Instead we say “An apple contains 100 calories.”  I wish his emails were this terse but I don’t read them anymore anyhow.

Summing this Up

Which is why I said at the outset that the crazy person who sends me the ranty emails is both right and wrong.  He’s right in the sense that calories are not a physically existing object.   But nobody but him (and Tim Noakes who went from provocative scientist to keto loony) ever said that they were.

But he’s wrong in his interpretation of that fact as, like many other aspects of the world, it is a relevant definition in that it represents the bodily metabolism of something physical that does exist (notably the macronutrients in our diet).  We simply use calories as a proxy for the metabolism of those nutrients and use shorthand non-literal terminology such as a “a food contains” or “we eat” X calories to talk about it.

So what does this all mean in terms of the calorie or energy balance model of bodyweight?  Well, that’s what I want to talk about next.  Some of this will tread the same ground as my article on Energy Balance and I’ll try to only summarize some of those concepts since the details can be found there.

Calorie/Energy Balance: Part 1

At the most basic level, we often talk about calorie balance which represents the difference between calorie intake (from food) and calorie expenditure (from a variety of components such as Resting Metabolic Rate, Thermic Effect of Activity and others).  If calorie intake exceeds calorie expenditure, we gain weight/fat (I’ll explain this momentarily).  If calorie intake matches calorie expenditure, no change occurs.  If calorie intake is lower than calorie expenditure we lose weight.   More technically we state that

Calorie Expenditure – Calorie Intake = The Change in the Energy Stored in the Body

Please note that that last term doesn’t even use the term weight but rather the change in energy stored in the body. This is explained in detail in the energy balance equation article along with more briefly below.

But conceptually what it says that is calorie intake exceeds calorie expenditure by say, 500 calories, those 500 calories will be stored in the body.  By extension, if calorie expenditure exceeds intake by 500 calories, those 500 calories have to be lost from the body (or the body has to adjust metabolic rate to compensate).

Now in keeping with the discussino above, clearly this isn’t true in the sense that calorie are not a physical entity that can be stored or lost from the body.  It’s not like money.  If I make 10 dollars more than I spend, I can stick those 10 dollars under my mattress so that the IRS can’t find it.  If I suddenly need to spend 10 dollars, I can remove it from the mattress for use.    Dollars are a physical entity that can be stored or removed and calories aren’t.

But as I’ll show in a bit more detail, that’s because, once again the idea that calories are stored or lost from the body is just a semantic shorthand and proxy for what is actually going on since it saves a lot of tedious writing.

A Primer on Digestion

Remember that at the end of the day we eat foods.  Foods contain the macronutrients in some proportion and amount.   So what happens when we eat those foods? Well they get chewed into smaller bits which starts digestion before getting to the stomach where enzymes break them down into their constituent molecules.  Some of the food will be lost to digestion and just show up in poop a day or three later but we only care about the food that is actually digested and absorbed.

After a bunch of toing and froing amino acids, glucose and fructose get dumped into the portal vein where they go to the liver while fat metabolism is way more complex than I want to describe (simply: most but not all fats go into the lymphatic system after being repackaged and eventually end up in the bloodstream).

But basically the foods we eat release nutrients that enter the bloodstream where they can be used by the body.  In the most general sense, there are two fates of nutrients in the body once they make it through digestion:

  1. They can be burned for energy immediately.
  2. They can be stored somewhere (somewhere meaning a variety of places such as the liver, muscles, fat cells or the nutrients just sit in the bloodstream in a holding pattern) for later use.

So imagine that you have eaten a meal containing some amount of protein, carbohdyrates and  You chew it up (yummm), it hits the stomach where it is digested and, when all is said and done, now you have say 25 grams worth of carbohydrate molecules floating around in the bloodstream.

Some of them will be metabolized by the liver or muscle and used immediately for energy and some will be stored for later use in the liver or muscle as glycogen.   Please note that carbohydrates are rarely converted to fat for storage.

Eating protein will produce amino acids into the bloodstream which have a number of fates including being burned for energy, converted into carbohydrates (or ketones) or used for protein synthesis.  Eating fat products bundled up triglycerides that can release fatty acids for energy or that can be stored in muscle (as IMTG) or fat cells as fat.

Like I said: two fates after you eat something.  The nutrients can be used immediately or stored for later.

Nutrient Balance

Now it should be obvious that even if all of the macronutrients (protein, carbohydrate, fat, alcohol) we might consume can generate heat during metabolism (measured in calories) to the body, they aren’t identical in many ways.

They differ in their primary roles in the body (protein being primarily structural in terms of building new tissues with carbohydrate and fat being primarily there to provide energy to the body), how they are metabolized and even in their relatively propensity to be stored or burned for energy.  And it is, quite factually, somewhat simplistic to talk only in terms of calories for this reason.

More accurate by far would be to talk in terms of nutrient balance rather than calorie balance.  This is conceptually identical with the difference between the intake and burning of a given nutrient determining how the amount of that nutrient in the body changes.  So consider carbohydrate for example.

Carbohydrate balance = Carbohydrate Intake – Carbohydrate Oxidation

If carbohydrate intake is greater than oxidation, carbohydrate balance will be positive and carbohydrate will be stored in the body.  The same holds for the other nutrients more or less.   I say more or less as there are differences in how well or poorly the nutrients are stored or used for energy (i.e. there is no store of alcohol and it all has to be burned off) but just keep the general concept in mind.

If intake is greater than burning, we get storage and if burning is greater than intake, we get removal.  If they are equal, there is no change.  So:

Protein balance = Protein Intake – Protein Oxidation
Fat balance = Fat Intake – Fat Oxidation

If you’re wondering about alcohol, well, alcohol is weird.  There is no storehouse of alcohol in the body and it will always be burned off for energy.  It gets weirder as controlled overfeeding of alcohol doesn’t generate the expected weight gain.  There appear to be missing calories when it comes to alcohol.

Calorie/Energy Balance: Part 2

So let’s put the above together.  Let’s imagine that you are eating 101 grams of carbohydrate per day and burning/oxidizing 100 grams per day.  By the nutrient balance concept, this means that 1 gram of carbohydrate will be stored somewhere in the body.

And that’s what happens: since there is an excess of 1 grams of carbohydrate in the bloodstream that didn’t get burned off, it had to be stored.  Now the body has one more gram of carbohydrate stored than it had a day ago.

Now, on the next day say you burn the same 100 grams of carbohydrate but only eat 99 grams of carbohydrate.   The body will now pull that extra gram of carbohydrate from the day before and put it through a whole bunch of metabolic processes that generate ATP.

The generation of ATP generates heat which can be measured in calories (alternately it may shift fuel metabolism to burn more of something else but I’m trying to keep this simplified here). We know that that during that process, enough heat will be produced from the metabolism/oxidation of the gram of carbohydrate to generate 4 calories (again, technically Kcalories)

Thus we can say, accurately now, that on the first day, the body stored 4 calories worth of carbohydrate.  And on the second day it used 4 calories worth of carbohydrate.  Again, this isn’t to mean that literally 4 calories were stored since calories are not a physical thing.

Rather, the body stored or mobilized 1 grams of carbohydrate that, when burned for energy yields enough heat to generate 4 cal.  It’s just a semantic shorthand.

If you store 10 grams of carbohydrate in the body and you have stored 40 calories worth of energy, if needed, the body can break them down and generate 40 calories of heat.  It’s semantic stupidity, once again, to focus on the words “store 4 calories” or “burn 4 calories”.

You’re not literally doing either but the storage of those 10 grams represents the 40 calories of potential heat energy which can be generated if they are oxidized metabolically in the body.

Calories are just a proxy for what’s going on.

Is this making sense?

Calorie/Energy Balance: Part 2

The same holds if you move up a level and talk about actual changes in tissue gain.  Consider body fat.  We usually say that an excess calorie intake of 3,500 calories is the equivalent of one pound weight gain.  Now this is incorrect on a lot of levels mostly because people lost sight of what the original concept was meant to represent.  Energetically, in terms of the potential heat energy that is represented, only one pound of pure fat contains ~3,500 calories.

The math works like this: 1 pound of body fat is 454 grams of tissue of which about 85-90% is actual stored fatty triglyceride (the other 10-15% is water and various cellular machinery but don’t get caught up on this).   By math, 454 * 0.85-0.9 = 385-410 grams of stored triglyceride.

Since each gram represents 9 calories of potential heat energy this is 3465-3672 calories, or about 3,500 calories.  In contrast, one pound of glycogen is only about 1800 calories (454 grams * 4 calories per gram potential energy), one pound of muscle is about 600 calories of potential heat energy if it’s broken down for energy and one pound of water is zero calories.

The point being that one pound doesn’t represent 3,500 calories of energy except in the case of fat.  It’s less for everything else.

And this is important because the proportion of glycogen, fat and muscle that is gained or lost during over- or under-eating can vary depending on a host of factors.    If someone is gaining 100% fat and overeats 3,500 calories, they will gain one actual pound of weight.  Muscle is way more complicated since, despite only containing about 600 calories of metabolizable energy, it takes ~2,700 calories to build that single pound.

Weight loss is a bit easier to explain this concept.  Someone losing 100% fat with a 3,500 calorie deficit will lose about one pound of weight.  But someone losing 100% muscle with a 3,500 calorie deficit will lose nearly 6 lbs of weight (3,500 calories / 600 calories metabolizable energy = just under 6 lbs).  Someone losing a proportion of fat and muscle will fall somewhere between those extremes and you can lose or gain water with no deficit or surplus whatsoever.

But once again, referring to this in terms of calories is just a semantic shorthand.   We are storing nutrients or building tissue that is built from those nutrients.  And those nutrients/tissue built from those nutrients represent a certain number of potential calories of heat energy when and if they are broken down for energy.

It’s just faster and less tedious to write that “Someone has a 500 calorie surplus” than to write that “Someone has a nutrient surplus resulting in the storage of excess nutrients that represents the amount of stored energy that would raise a certain amount of water by a certain number of degrees C if the body were required to oxidize it for energy.”

Beating the dead horse, it’s just semantic shorthand where the potential calorie generation of a given surplus is used as a proxy for what’s actually going on.  We eat food which contain nutrients which can be burned or stored in the body and which represent the potential to generate an amount of heat that can be measured in calories if and when those nutrients are burned.  So, as with the general concept, while calories are not technically a physical or actual entity, they are a proxy for something that is.

And while I in no way expect this to change the mind of the crazy Internet person that stimulated it (he tends to duck and dive when faced with facts he can’t ignore), hopefully everyone who read it burned lots of calories doing so.

Get it?

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