Do Calories Matter?

There is a debate that seems to have come up recently about whether the calories in the food you eat matter. To understand this debate better we probably all need to understand what a calorie is.

Technically when you turn over some food package and see that it has 100 calories in it that actually is 100 kilocalories which is equivalent to 100,000 calories. To make things simpler, my guess is because the US is not on the metric system, someone made the decision to shorten that calories instead.

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

So if a food label says that a food item has 100 calories in a serving that means there is enough energy in that food to raise 1 gram of water by 100,000 degrees celsius.

To measure the amount of calories in a food, scientists would traditionally place a food in a device called a bomb calorimeter which would burn the food and measure the rise in temperature in the water within the device.

Scientists realized that we cannot take the calories produced within a bomb calorimeter and say that is how many calories are produced when we eat the food because we don’t use the entire food, we excrete unused parts of the food in our urine and feces.

In the late 1800s a scientist named William Atwater (Atwater System, n.d.) refined the amount of calories in food by placing a food in a bomb calorimeter to determine its caloric value and then feeding the same food to a group of people. He then collected the urine and feces of these people, put that in a bomb calorimeter and measured the calories excreted in the waste of these people. Once he had the total calories of a food and how many calories were excreted in the waste from his human subjects he could calculate the net calories used.

In addition to coming up with some more accurate caloric values for these foods Atwater was also able to come up with caloric values for the three major macronutrients that make up every food we eat. Protein contains 4 calories per gram, carbs contain 4 calories per gram, and fat contains 9 calories per gram.

Knowing how many calories were in each macronutrient was a huge step forward because it allowed us to just figure out what the macronutrients were in the food and then use the calories per gram values from above to figure out the total calories.

This is all great science, and Atwater’s work to calculate the net calories in food as well as the calories per gram of each macronutrient was a huge step forward in calculating the energy within foods. However human physiology is quite complex and there are a number of processes that go into how we extract energy from food. We certainly don’t combust foods like is done in a bomb calorimeter.

We also cannot assume that the way I digest a food is going to be the same way you digest a food. It is likely that each person digests a food differently and extracts a different amount of energy in the process. So while Atwater calculated the net energy values of foods within human subjects that is not representative of how every human body extracts energy from its food.

But there are other factors that determine the amount of energy we extract from food as well.

The way a food is prepared can affect the amount of energy we utilize from food.. For example there will be different amounts of energy extracted from a steak that is cooked rare vs well done.

In addition to that we have the variability in the amount of energy it takes to digest a food. That’s right, we have to expend energy to extract the energy in the food. The more processed a food is the easier it is to digest. Consider 20g of protein from a protein shake and 20g of protein from a chicken breast. Both contain 20g of protein and based on Atwater’s calculation that would mean there are 80 calories in both foods. However it will take much more energy for our body to digest the chicken breast than the protein shake so we might net 75 calories from the protein shake but only 60 calories from the chicken breast (I am just making up numbers here but you get the idea).

Then consider what the FDA allows for variability in the calories listed on a food that comes in a package or box. The FDA will allow up to a 20% variance in the calories listed on the label. So that food that says it has 200 calories could actually contain 240 calories or 160 calories. Since lower calories are viewed as better, what do you think the food manufacturer is going to put on the label?

At this point you are probably thinking calories are useless.

Why do we even need calories?

I mean our ancestors didn’t have labels telling them the nutritional information of what’s in their food and they survived!

The need to try and figure out how many calories are in our food has arisen because our overconsumption of food is a major reason for the rise in health conditions. We tend to think information is all that is needed to make health changes. However information is not the barrier to being healthy, it’s putting that information into practice in the context of our lives.

Just because you tell someone this food has 200 hundred calories in it does not mean they are not going to overeat later on. Even if they tracked all the calories they ate and knew exactly how many they needed to be in energy balance (which is impossible to tell) what happens when they hit that calorie limit and someone puts a fresh baked cookie in front of them? 99.9% of people are going to eat the damn cookie!!!!

The reason people overeat does not just have to do with the fact that they didn’t know how many calories are in food, it’s much more complex than that.

So why did our ancestors not have to know how many calories were in their food?

For one, food was not abundant, they didn’t have access to food 24/7 365 days a year like many people do today. They could eat as much as they wanted, and most likely did, but once the meat from the animal was gone, or there were no more blueberries on the blueberry bush, they had to wait until they came across more food or killed another animal.

Today, “the blueberry bush” never runs out of blueberries.

Another reason our ancestors didn’t have to worry about their energy intake has to do with the foods we consume today versus what we consumed less than 100 years ago. We evolved alongside the foods we consumed. This symbiotic relationship allowed us to develop mechanisms to judge when we have eaten enough of these foods. The Cheeto and other ultra-processed foods on the other hand is a relatively new food and everything about it is unnatural. These foods make it easy to override the mechanisms to determine how much of a food we should eat because frankly we don’t know.

The combination of modern foods plus the widespread availability of food sets us up for the perfect storm to over consume energy.

We can try and control the type of foods we consume by consuming as much whole foods as possible, but even if we do that, the food never runs out. Like I said above, the reason we eat is much more complicated than before, and even if we are not hungry, but are stressed, tired, sad, celebrating a special occasion, we are still going to want to eat, and the food, whole or processed, is still there when these things happen.

Plus very few people are going to consume 100% whole foods.

In our modern world we need some way to track the amount of energy we are consuming.

Calories are one way to do this.

Is it going to be an accurate representation of how much energy you consumed?


Could you still over consume energy when tracking them diligently?


However if you are consistent about it and do it for several weeks you should be able to see if you are eating too much, too little, or just the right amount.

If over the course of several weeks you notice things like the scale moving in a direction you don’t want it to, or have other subjective signs that your caloric consumption is off, you can adjust your caloric intake while keeping everything else the same and it should get you on the path you want to be on.

If you keep consistent over the weeks and months and keep making tweaks you should be able to manipulate your food intake to get you to the energy consumption you are after.

Will the end caloric number that finally gets you heading in the direction you wanted be accurate?

Most likely not. It may be off by several hundred calories. But that ultimately doesn’t really matter, you are just using calories as a way of adjusting your energy intake to the point you are moving in the right direction.

Part of the problem I think people have with tracking calories is that they are not patient enough or consistent enough with tracking them. The first sign that it’s not getting them the results they want and they give up and say tracking calories does not work.

However as you will see, this problem is not specific to calories, it’s a problem with any way we choose to quantify our energy intake.

That all said, tracking calories is not for everyone and it is not the only option to tracking your energy intake.

You can use another just as controversial tool to track energy intake, the scale. Of course the scale gets just as many criticisms from people, and many of those criticisms are valid. However, in general it can be a good tool to track energy intake. If it goes up, you are likely eating too much energy, if it goes down you are likely eating too little, if it stays the same you are likely eating the right amount to meet your caloric demands. In fact I think the combination of tracking calories and using the scale as a feedback mechanism to know if you are consuming the right amount of energy is a good combo and is the one I use myself.

Of course the scale can fluctuate for a whole bunch of reasons, and just like tracking calories you need to be consistently using it over the course of several weeks to see the real trend line. Even then it could be going up, down, or not moving at all because you are gaining or losing muscle, or even making an even trade off between muscle and fat. I have discussed the best way to use the scale in other posts so I will point you there for more detailed information. But the quick solution to making sure the scale is providing you the right information is to have a second measure of body composition to back up the changes you see on the scale.

The final technique you can use to track energy intake is the hand system. Using this method you use your hands to estimate the amount of energy you are eating. Precision Nutrition has some great resources on this method, this infographic from them pretty much sums up how it works.

They also have this great guide here, as well as a very comprehensive FAQ. Again, just like with tracking calories, or using the scale there is a margin of error and you will need to monitor your body composition to determine if you have nailed the amount of energy you are eating or need to adjust it.

I think we need to move away from the debate about calories and whether they matter or are accurate and come to the consensus that what we are really trying to do is quantify and track our energy intake.

In general, the more whole foods you consume the less you will need to worry about quantifying your energy intake. It’s just too hard to overeat them.

However we live in a modern world where we have access to as many whole foods as we want whenever we want, as I said above the blueberry bush never runs out of blueberries today. That constant and immediate access to food can be problematic. In addition, we now have ulta-processed foods that our body has a very hard time regulating. So living in this modern world presents a bunch of challenges around regulating our energy intake, so having a way to track our energy intake can be beneficial.

Whether you choose to count calories, use the scale, or use the hand portion system, it doesn’t really matter You can be successful no matter which method you choose. Each one has its benefits and flaws, what matters is you choose the one that works best for you!

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Atwater system. (n.d.). Wikipedia. Retrieved May 8, 2023, from

3 thoughts on “Do Calories Matter?

  1. Great post, Ryan.

    1. Thanks!

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