What are calories? Is a calorie something you burn?

Well, calories are quite literally energy. Like, literally energy. You can’t see them under a microscope, they aren’t a molecule that has a structure, and they don’t have a chemical name.

Calories refer to the energy that can be extracted from the nutrients (food) you consume. To be precise, calories are a unit of measurement of heat.

When we refer to calories in nutrition, we are really referring to kilocalories or kcals. This is where we confuse the hell out of you by telling you that the “calories” listed on food labels are actually “kilocalories” (within the metric system, “kilo” refers to a thousand of something, so in our case, a “kilocalorie” is technically one thousand calories). So, if a label says 100 “calories” it’s actually 100 kilocalories and 100,000 calories.

You see, one calorie is the amount of energy it takes to heat up one gram of water by one degree celsius. 

If it sounds confusing, don’t worry too much. Just know that the food calories I talk about are a bit different than the ones you’re accustomed to hearing about and using in your high school physics class.

Try not to get too caught up in the details. It’s just important to remember that we will use “calorie” when we are actually referring to kilocalories because it’s simply the popular way to refer to them.

With that distinction out the way, if you see either the term “calorie” or “kilocalorie” throughout this, we are referring to the stuff on the back of your food label.

The other important takeaway is that the term “calories” refers to energy, something measurable. We don’t want calories to be abstract concepts.

So when we say fat has 9 kcal per gram, that means that one gram of fat contains enough energy to heat 9,000 grams of water by one degree.

Why does this matter? Well, what ultimately determines weight loss is how much energy you consume versus how much energy you expend. 

So let me introduce you to the “Energy Currency of our BODY”

ATP: adenosine triphosphate

I know what you’re thinking. “What the hell does heating up water have to do with gaining or losing fat? & What is this Fancy name (ATP) need to do with losing fat from the body? ” Great questions; I am glad you asked.

Our body is an amazing machine with tens of thousands (if not hundreds of thousands—we didn’t count them all up, deal with it) of metabolic reactions occurring simultaneously, all to make you exist and do the Stuff you do every day.

Some of these reactions produce energy, but many of them require energy input.

Even some of the most basic things, like maintaining your sodium/potassium gradient across your cell membranes, require energy.

But energy is basically a measurement. It’s not really a tangible thing, so in order to provide this energy to run these reactions and processes, our body uses an “energy currency” called adenosine triphosphate, or ATP.

Why do we call it an energy currency? Because it acts a lot like monetary currency.

Have you ever thought about why currency developed all over the world? I mean, at the end of the day, it’s just a silly piece of paper.

If you took a million dollars in cashback in time 10,000 years, you couldn’t buy a damned thing with it. The pieces of paper themselves are not valuable because the currency itself is not what is valuable.

It’s what the currency represents that is valuable. We developed currency for a very practical reason. It was impractical to barter your goods and services for every transaction.

Currency is a universal way to exchange value. ATP is not all that dissimilar from monetary currency. Many reactions require energy input to power them, and energy is measured as “heat.”

If you want to know the intricate details of how this works, you’ll find out if you ever take a biochemistry class.

But basically, ATP is 3 phosphates attached to adenosine. Those three phosphates are “high energy,” and when ATP “donates” one of them to a reaction, that high energy phosphate gets all up in that reaction’s business and pushes it forward even if it would otherwise be energetically unfavorable.

Using these ATPs in this fashion is “spending” energy currency, that is, the “calories out” part of the energy balance equation.

Exercise 

Let’s elaborate a bit further. We’ve all been told to exercise to increase our caloric expenditure (calories out), but why does exercise “burn calories?” Or perhaps a more accurate question is why does exercise “spend energy (ATP)?”

There are quite a few reasons, but let’s start at the most basic. Movement requires energy. To move, your muscles have to contract.

Contractions require cross-bridging between contractile filaments called actin and myosin. When actin and myosin form a cross-bridge, they can pull each other closer together.

Muscle contraction

Deep inside Muscle Cells

When these cross-bridges happen all along the length of a muscle (that has thousands of cross-bridges at once) the muscle contracts and moves.

That process requires ATP, and thus the body has to “spend” energy to move those muscles. Other processes like increased heart rate will also require more ATP, as it is involved in the process of muscle contraction in the heart.

In fact, there are likely so many processes that “spend” ATP that we would have difficulty naming them all. The point is that your body needs to make this ATP to function for even the most basic processes.

Every cell can make and use ATP, although cells with mitochondria are way better at making ATP than cells without mitochondria, (that’s a topic for a different blog Series).

So how does ATP relate to your gaining or losing body fat? Is your fat just a bunch of stored ATP that gives you a belly and makes it hard for you to get noticed by the opposite sex at the beach? Not really.

ATP can’t really be stored to any large degree. It’s a very high-energy molecule, so the body tends to only make the amount of ATP it needs at any given point. If you need more energy, your body just ramps up ATP production.

But since you can’t store ATP, evolution had to come up with another way to store energy so you didn’t die. Because if you run out of ATP, that is exactly what would happen.

Therefore, if you consume more energy than you need to produce the right amount of ATP, your body finds a way to capture that energy so it can potentially produce ATP later.

This energy can be stored in a few different ways, but the major energy bank of the body is adipose tissue or body fat.

Do you remember all of that metabolic adaptation stuff I talked about in the previous blog series? Think of this as the backstory to why we metabolically adapt. And the backstory only goes deeper.

FAT CELLS (Adipose Tissue) — The Body’s Energy Bank

Adipose tissue is made up of adipocytes, which are cells that store massive amounts of fats in the form of triacylglycerides (TAGs).

Abdominal FAT

inside the Fat Belly

  You can also store energy from carbohydrates in the form of glycogen, but this storage is limited to around 300-400 grams in the liver and another ~400 grams in your skeletal muscles.

That may seem like a lot, but it really isn’t. That’s less than 1000 grams of total carbohydrate storage adding up to well under 4000 kcal of stored energy (carbohydrates contain 4 kcal of energy per gram). Whereas adipose stores massive amounts of energy.

Take an average-sized, non-obese male at 80 kilograms and 15% body fat. That would be 12 kilograms of body fat or 12,000 grams. This equates to almost 94,000 kcal of stored energy, and this is someone who is not overweight or obese.

PROTEIN

Protein, the other major macronutrient in our diet, doesn’t really have a storage mechanism. It can be used for protein synthesis or oxidized for energy, but there isn’t a viable storage mechanism.

That doesn’t mean you just “pee or poop it all out” as some people have claimed. Just because there isn’t a storage station for protein the nutrient, doesn’t mean your body can’t capture that energy another way.

Proteins are made up of amino acids, and the body has mechanisms to obtain energy from them. One of the major ways is through the process of gluconeogenesis. That’s a big word, but it just means the process of forming glucose from non-carbohydrate substrates in the liver.

Around 60% of the amino acids (the nitrogen-containing building blocks of proteins) are gluconeogenic, and their carbon skeletons can be used to form glucose once the nitrogen is removed.

It’s possible that this glucose can then be stored as glycogen and theoretically fat, but it’s a small amount since protein is a more inefficient energy storage source compared to carbohydrates and fats. Don’t worry, because there will be more on that later.

However, there is an interplay between these three macronutrients inside the body. As I’ve already discussed, the carbon skeletons from amino acids in protein can be converted to glucose, and glucose can actually be converted to fat via a process called de novo lipogenesis (DNL), which occurs in the liver and adipose tissue.

You Might think 🙂

Ah-ha! So that’s how carbs make you fat right? Well, not really. DNL actually contributes a very small amount of fat to body fat storage.

In fact, a recent study examined overfeeding women by 50% above their maintenance calories (the number of calories/energy where these women maintained their weight).

Through sophisticated methods, they were able to show exactly where the stored body fat within these women came from carbs or fats.*1

What did they find?

That the female participants, on average, stored a total of 282 grams of fat per day in adipose. A negligible 4 grams of that fat resulted from DNL, and 278 grams came from dietary fat. So carbs only contributed to 1.4% of fat gain during overfeeding in this study.

So, if carbs aren’t being stored as fat, then it must be dietary fat that is making us fat, right? Based on the last study, it has to be. After all, a whopping 98.6% of the body fat the women stored came from dietary fat.

But let’s not go crazy yet. Just as carbs have been the most recently demonized macronutrient, fats also had their trial by fire and were once theorized to be the single cause of obesity.

While it’s true that the body has an easier time storing dietary fat as body fat because there is little conversion required, the amount of dietary fat that is stored as body fat also depends on how many carbohydrates you consume.

Say what? Well, carbs and fats are the two major fuels for the body from which ATP can be produced, and the intake of one affects the metabolism of the other.

If you’re on a high carb diet, you might not store virtually any body fat from the carbohydrates themselves, but the carbohydrates increase the secretion of insulin which impairs lipolysis (the breakdown of fats) and fat oxidation—the two crucial steps of the fat-burning (and therefore body fat losing) process.

Ah-ha! So it actually is those annoying carbohydrates making us fat!

This is what supporters of the carbohydrate-insulin theory of obesity believe, but more on that later. Like every other physiological occurrence, it isn’t quite so simple.

End of Part 7

to be continued…

*1 (n.d.). Short-term alterations in carbohydrate energy intake in humans …. Retrieved August 20, 2018, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC185982/