Anyone who is trying to lose weight has heard about calories. Not everyone who loses weight counts or tracks their calories, though. That leaves many people confused and wondering, do calories really matter?

Let's start with a resounding YES. There is no debate that a person's body weight is determined in no small part by the balance of how many calories they eat versus how many calories they burn. Unfortunately, as simple of an equation as "calories in - calories out" seems to be, it's actually much more complex. What is a calorie exactly? Very simply a food calorie (which is 1000 calories or 1kcal in chemistry/physics) is the amount of energy that it takes to raise 1 kilogram of water 1 degree Celcius. Heat = energy. Think "If I burned this food, how much would it heat up water surrounding it?" That's a calorie.

Calories In

So let's start with the calories in part of the equation. We all know how many calories are in our food, right? We can look on the packaging or look it up on google or a calorie tracker. Easy peasy! Right? Not so fast. Those calorie amounts are not, actually, completely accurate. To start with, many calorie counts aren't determined by actually surrounding the food (sealed into a container) in water and burning it. Rather, it is determined mathematically by looking at the protein, fat, carbs, and alcohol in the food and determining how many calories each of those contains. For reference, each gram of fat contains 9 calories, each gram of alcohol contains 7, and each gram of carbohydrates and each gram of protein contains 4 calories. These numbers themselves were determined by burning and averaging. But that means that maybe some of the grams of fat you ate contain fewer than 9 calories per gram, and maybe some of the carbohydrates actually contain more than 4 calories per gram.

Since each individual food doesn't have its calorie counts directly measured, that means the number on the package is an estimate. Even for whole foods, not every organism is the same. Just as we all have different body compositions and may have more muscle or more fat, or more or less glycogen stored in our muscles. The same is true for animals and even plants. Without actually testing every single food you put in you body, it's impossible to get EXACT calorie counts. So the calorie counts we see are estimates. They are good guesses, but definitely not exact.

Sound complicated? It gets worse. The amount of calories in a food are the maximum energy your body can obtain from eating that food. We aren't perfect machines, after all, we don't digest everything completely which means we leave some calories behind. Typically, our bodies absorb the most calories from carbohydrates and the least from protein. Raw plant food is harder for our bodies to digest, if our digestive system doesn't break down the cell walls that means it cannot absorb the nutrients held inside. Then there are different types of carbohydrates such as resistant starches, which our body is unable to break down and use. Some foods like nuts, though they are high in fats and thus high in calories, are not completely digested and so we don't absorb all of those calories. And of course, how many nutrients you absorb from your food is also effected by your own individual differences, such as what bacteria are in your digestive tract to break down the foods, and how healthy your gut is. Diseases like Celiac or Crohn's cause inflammation which makes it harder for your body to digest the nutrients you eat.

TLDR; Calorie counts are estimates at best, and don't take into account what ultimately gets absorbed by our bodies.

Calories Out

We have finally made it to the other half of the equation! Are you tired yet? Man I'm tired writing it all out. Anyone else need to take a break? Phew. Ok.

So for this half of the equation we'll be starting where we left off. Digestion! There is this idea out there about "zero calorie foods" which was brought up by the lovely Laura in my facebook accountability group. The concept is that these are foods that take as many calories to digest as they have in them so the net effect is zero calories. Is this the case? How many calories do we really burn from digestion? Well, this all depends on what the source of the calories is. The fancy term for how many calories it burns to digest a food is called the "thermic effect." Fats take the least energy to digest, with a thermic effect of 0-5% in general, sometimes 15% max. Then there are carbohydrates, with a thermic effect from 5-15% depending on the type of carbohydrate. Protein takes a lot of energy to digest, coming in at 20-35%! Besides the specific fat, carbohydrate, or protein being digested, the energy needed to digest foods is also is determined by your body. It depends on your insulin sensitivity and is thought to increase after exercise, etc. But as you can see, none of these are even CLOSE to 100% which would be a "zero calorie food." That doesn't mean these foods are bad, but they are more like very low calorie foods, not zero.

Once the calories are digested and absorbed, how do we know how many we are burning? You may see my answer coming by now. For most of us- we don't, exactly. Let's start with our resting metabolic rate (RMR). That's the fancy term for how many calories your body burns at rest just to make everything in your body function- to keep you breathing, your heart beating, your neurons firing, etc. There are some simple ways out there to calculate it, which makes it seem simple to figure out, but these calculators are estimates at best. Everyone's body is different and your RMR changes. It changes depending on body composition but also depending on your eating habits- your body adapts its energy usage depending on how many calories you take in. If you take in too few calories for too long, your body becomes more efficient and uses fewer calories to keep the system running. Most estimates of RMR are based on sex, height, weight, and age. To be more accurate, there are equations which take body composition into account but those are still not hugely accurate. The most accurate way involves using a device that measures respiratory gasses to determine the amount and type of fuel (fat, carbs, protein, even ketosis) being burned by the body. Most of us don't have access to this technology so our estimates of RMR are, much like our estimates of calories consumed, more like an educated guess.

How about calories burned from exercise? Can't you find that out just by looking at your fitness band or the screen on your cardio machine? Not really. The amount of calories you burn during exercise, as with everything else, depends on a huge number of factors. Body size, composition, how efficient your body is at that specific exercise, etc. As with RMR, exercise calories are typically calculated based on your age, height and weight, and sex. This, again, isn't very accurate. Fitness trackers can be slightly more accurate, if they add heart rate into the equation. To really be accurate, you'd need to measure your oxygen consumption during exercise, which again is done by measuring respiratory gasses. Most of us don't have access to that level of accuracy. It's also important to note than MANY of the equations to determine calories burned during exercise give you a much higher number than you actually burned.

So What Do We Do?

Now that we are aware of how inaccurate calorie measures really are, you may be wondering why we should even bother counting them? It's the same reasons why it's important to measure your weight frequently even though weight isn't an accurate measurement of body fat. Because an inaccurate measure is FAR superior to none at all and because it keeps you accountable and aware of what you are doing. But it DOES mean that there are no easy equations, and it's important to make adjustments based on what YOUR body tells you. For one, it's not necessary to hit an exact calorie count. It's better to have a range, which allows you to eat more on days when you are hungrier and less on days where you aren't as hungry. Ultimately, since your count will be mostly an estimate, even if you hit an exact number every day based on nutrition labels, you're still eating within a range. You're just causing added unnecessary stress to the equation. Track your calories and see, over the course of a few weeks, what effect it has on your weight. Readjust if your weight isn't doing what you want it to do. If your goal is losing weight, find the highest amount of calories you can eat while still losing weight and make the higher end of your range just above that. If your goal is to maintain, find the calorie range where your weight stays the same across multiple weeks. Congrats! You've found a more accurate measure of your personal RMR! THEN add in exercise. Eat on the higher end of your range on the days where you are engaging in longer or higher intensity physical activity, if you really want to you can try increasing the high end of your range slightly to account for calories burned. Ultimately the calories IN portion we have much more control over than the calories out, so focus the most on that.

Are all calories equal? Clearly not, not in how they enter your body or how they are used. However, that doesn't change the fact that, ultimately, your weight IS determined by calories in, calories out. It is absolutely critical to eat fewer calories than you burn. If you don't do that, you will not lose weight. Period. However, just because your body may not react the way to expect it to from guestimates on how many calories your body is getting doesn't mean that it's because calories aren't necessary to pay attention to. It is because your estimates are off. The problem isn't in the calories themselves, it's in the measurement.

Here's an analogy. You are cooking pancakes, and the recipe calls for 1/3 cup of milk but you only have a 1 cup measuring cup (with no other measures indicated on the cup.) So you are eyeballing your amount for 1/3, but it's not very accurate. Your pancakes don't turn out how you expect. Chances are, you didn't use the right amount of milk. Or maybe the recipe is off. It's not the milk itself that was the problem. You will have to adjust how much milk you put in next time, and it will be right. Over time, you learn the right amount of milk based on the consistency of the batter and maybe you learn how to do this without measuring at all. Awesome! That doesn't mean the amount of milk isn't important. Same with calories. Sometimes it takes some trial and error to get the amount right, and sometimes you can get the amount right without measuring them, but that doesn't mean your results weren't from getting the right amount of calories.

Cause and effect. It's hard to deny, and this is why I am such a HUGE advocate of tracking. Tracking your weight (daily!) and tracking your calories AND your macros. Because if you don't know what you are putting into your body, you don't know what is causing your weight to change (or not.) Hopefully all this information didn't turn you against the idea of tracking calories, because it is still extremely helpful, but only when we are aware of the limitations. And all these quirks can help us to hack our food choices when we need to eat more, feel more full, etc, without blowing our calories out of the water. It can be overwhelming, though, and sometimes it can help to find someone you trust to help you navigate all the complex little details.

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