Blog Post

Unpacking Common Criticisms of the Calories in vs Calories Out (CICO) Model

Unpacking common critcisms of calories in vs calories out

Calories in vs calories out is a concept that is commonly criticised. People will say that it is “outdated” or “overly simplified.”

There can be validity to certain criticisms. But the existence of the calories in vs calories out model cannot be debated at this time. Without a doubt, it exists.

The finer points of the model can be debated, but the overall model is relevant.

Although it appears simple as an equation, the factors that go into the equation can have endless complexity.

One thing that can be said about the CICO model is that for every criticism of it, there is a logical answer. This is not something that can be said for other models of weight management, which I will discuss too.

In this post, I wanted to go through common criticisms, unpack them and address how they fit into the CICO model.

If there is anything I miss, it is not intentional. There is no gap I am trying to avoid or anything. I am just trying to cover common criticisms.

Understanding the CICO Model

The obvious starting point is understanding energy balance and the CICO model.

The body is made up of calories.

For example, fat and muscle are made up of ~7,700kcal and ~1200kcal per kg respectively. Amongst other things, they are literally stores of energy.

Each day we consume a certain number of calories. And we expend a certain number of calories.

Our energy expenditure changes daily due to a variety of reasons. But a brief look at where our energy expenditure goes can be found below.

Energy Expenditure Chart

Calories are a unit of energy. And energy cannot just disappear. If you consume more calories than you burn, it must go somewhere. Since we have storage forms on our body, such as muscle and fat, that can be where it can be stored.

If we consume fewer calories than we burn, this creates the opposite issue.

If we have used more energy than we have consumed, that gap must come from somewhere. Since we have internal stores of fat and muscle, it can come from these internal stores.

This gap is also known as a “deficit,” which is why it is called a calorie deficit. And it is also why by definition a calorie deficit must lead to weight loss over time (excluding changes in other variables such as water weight).

There is a lot more that can be said about the CICO model, but I will try to go through some of those aspects in the criticisms below.

Calories in vs Calories Out Doesn’t Account for Hormones

A common argument is that CICO does not account for hormones.

I have seen this taken further by some saying, “while a calorie deficit will work for a lot of people, it will not work if your hormones are off.”

Firstly, as mentioned, the definition of a calorie deficit involves weight loss over time.

If somebody is not losing weight after multiple weeks, they are not in a calorie deficit. The only exception to this is significant changes in non-fat/muscle weight such as water weight.

But the more significant aspect of this criticism to address is that CICO literally does account for hormones.

Hormones affect both calories in AND calories out.

Hunger Hormones Graph

Hunger hormones such as leptin and ghrelin typically play a role in our calorie intake.

The calories out portion of the equation is affected too though.

Using an example: If you have decreased thyroid levels (T3 and T4), your energy expenditure will be lower.

It is hard to quantify, but based on the evidence, it can be concluded that certain cases of hypothyroidism have as much as a 25% decrease in resting energy expenditure.

This is just one example.

Our food intake also affects our hormones too, for example. It is a cycle where both aspects affect each other.

This criticism of CICO is just oversimplifying the model to the point that it is not acknowledging that the calories out portion of the equation is a moving target that is multi-factorial.

There is More to Nutrition Than Just Calories

Healthy Eating

Calories in vs calories out is a model for understanding weight management. But it is not a dietary approach.

With this criticism, I wholeheartedly agree. There is way more to nutrition than just calories.

But just because there is more than one aspect does not mean we should not care about calories.

This would be like somebody saying, “there is more to nutrition than just micronutrients.” They are not wrong. But we should still care about micronutrients.

We can acknowledge one thing without ignoring everything else.

It’s Not Calories, It’s Insulin

Insulin is a hormone, but I wanted to give it a section for itself.

There are common variations of statements like “The key to weight loss is to control your insulin, specifically, keeping insulin as low as possible.”

Often followed by “the solution is to keep carbs as low as possible” 

Insulin’s main role is to take glucose from the blood and put it into muscle or fat cells to be stored for later use 

Insulin inhibits lipolysis, which is the breakdown of fat. 

It also increases lipogenesis, which involves taking fat from the blood to be stored as body fat. 

Lipolysis and Lipogenesis

You can see why this sounds scary. 

But the reason insulin inhibits fat breakdown is that you just consumed food. It is more efficient to use those nutrients instead of your body’s stores.  

And it is not like only one thing can happen at a time.

Other hormones like glucagon do the opposite of insulin and stimulate lipolysis. These hormones do not just completely switch off because insulin is present.

Think of this process more like a dimmer switch on light instead of an on/off switch.  

Insulin can also only store something that is available to be stored. If you are in a calorie deficit each day, there is less total glucose and fat available to be stored each day. 

A metabolic ward study by Kevin Hall and colleagues was done under relevant conditions. There were the same total calories, but one group was keto and the other was low fat.

Both groups lost the same amount of fat, even though insulin was 22% lower in the low-carb group than in the low-fat group. 

Additional Thoughts on Insulin

A few things I wanted to add to this section are:

  1. Protein also raises insulin. In some cases, it raises it as much as carbohydrates do.

    Often those who view insulin as the driving factor for weight gain only focus on the carbohydrate aspect. Meanwhile, protein is still promoted. If it was as simple as just insulin, this would not necessarily make sense. But nothing is ever as simple as just one hormone/aspect.
Graph showing protein + carbs raising insulin more than carbs
  • As mentioned, the CICO model can provide logical answers to every criticism. What about the insulin model of obesity?

A big question worth thinking about: What do you do if you want to lose weight, but are already in ketosis, have low insulin levels and are not losing weight?

Do you double down even harder on a ketogenic diet? Do you increase fat further and reduce carbohydrates even more? What happens if that does not work?

Luckily we know due to research such as the Kevin Hall study mentioned above that while insulin plays a role, it is not the driving force.

With the CICO model it is simple. Either calorie expenditure needs to increase, or calorie intake needs to decrease. Simple does not make it easy. But at least there is a solution.

Quicker Initial Changes on Low Carbohydrate Diets than Low-Fat Diets

A lot of people notice that they personally have a better response to either a low carbohydrate or a low-fat diet.

One thing that is worth adding to this discussion is that when analysing your own personal response, you should also factor in non-fat and non-muscle changes in scale weight.

What I meant is that when you reduce carbohydrate intake, glycogen levels deplete. Glycogen helps us hold onto water.

This can lead to a quick initial drop in weight, beyond just what is being lost from fat.

Glycogen and Water Weight Tweet

Vice-versa, if you have been low carb for a while and then have a high carb day or two, your weight will likely increase rapidly at the start.

When self-analysing without factoring this in, you could conclude that your body personally responds poorly to carbohydrates. You could think that you gain weight quickly whenever you add carbohydrates in.

But this is just how the body responds in the short term. Glycogen and water weight are not bad things either. Most people care about fat loss, not glycogen loss.

This is also why it is useful having research showing that in the long term when calories are matched, low-carb and low-fat diets lead to similar fat loss. This occurs in both controlled and uncontrolled settings.

The part where a personal response to each approach comes into play is the execution side of things. If you prefer one approach or find it easier to be consistent with, it is likely that you will get better outcomes over time with that approach.

It’s Not About the Calories We Consume, It’s About the Calories We Absorb

An argument that some people have is that CICO does not account for the digestion and absorption of calories.

This can be looked at from a few angles. Looking at common ones:

  1. Improving gut health means that we can absorb food and nutrients better.
  2. Different foods lead to different thermic effects of food, which affects our calorie expenditure.
  3. We absorb different amounts of different foods.

I will go through these individually.

Improving Gut-Health Means That We Can Absorb Food and Nutrients Better

Clearly, our gut health plays a role in how we absorb our food.

I do not think this idea plays out the way many people think it does.

A lot of people assume that better gut-health = weight loss for those who have excess weight they want to lose.

There is certainly merit to that thinking as a general concept.

Digging into this specific example though: If somebody had poor gut health and was not absorbing calories well, why would improving the absorption of those calories lead to weight loss? Would that not contribute to weight gain?

Using an example: When people who have coeliac disease consume gluten, it causes inflammation in the small intestine. This inflammation reduces the surface area and reduces the absorption of nutrients.

Villi and Microvilli

When these individuals stop eating gluten, on average body weight increases a bit for those who were initially underweight. This is due to now absorbing food better.

Regardless of how you look at it though, instead of viewing this as a criticism of the model, I view it as part of the model.

Instead of the calories that enter our mouth being what matters for CICO, it is the metabolizable calories we digest and absorb.

It makes the model less accurate to track. This leads to our next criticism that I will address after going through the rest of this section.

Different Foods Lead to Different Thermic Effects of Food, Which Effects Our Calorie Expenditure

This criticism is the easiest to address. The thermic effect of food is already part of the calories out portion of the equation.

On average, it explains roughly 5-15% of our energy expenditure.

It is higher for those who eat more total food, more protein, and more fibre. It is lower for those who do the opposite.

Once again, the calories out portion of the equation is not a static number. The things we do each day affect it.

We Absorb Different Amounts of Different Foods

Kilojoule absorption of tree nuts

A classic example people use is that we absorb ~70-85% of the calories from nuts. Other foods like white sugar could be closer to 100%.

Nuts are a bit of an outlier, which is why the example is often used.

But this concept does not break the CICO model. It improves it.

Pretending details like this do not matter is silly. Factoring them into the model is the key.

It adds complexity. But as you can tell already, while the equation is simple, the variables that go into it are complex.

As mentioned, CICO is not a dietary approach. If you track calories and ignore this aspect and pretend all foods are equal in absorption, this could lead to issues.

If you are consistent with your intake and adjust things over time based on what happens, it does not really affect things much though.

We Cannot Accurately Track Our Calorie Intake or Expenditure

There are a few reasons we cannot track our calorie intake or expenditure easily.

A lot of people assume that because they track their calories, they KNOW how many calories they are eating each day. But there are still some assumptions built in that might not be entirely accurate.

One aspect is the section above about how absorption levels differ for a variety of reasons. And then also factoring in the thermic effect of food.

Then also factor in:

  • Accidentally tracking food incorrectly.
  • Forgetting to track stuff.
  • Potential food labelling issues. There is also a margin for error here.
  • Multi-ingredient foods can have a different ratio of ingredients in the X gram amount you poured out.
  • Estimations of the fat/protein content of meat portions, that differ slightly each time.

It can turn into an endless list. No matter how hard you try, there is some level of inaccuracy.

With calorie expenditure, we can do some stuff to get estimates of our expenditure easily. We have calorie calculators that can provide an estimate. There are watches that estimate energy expenditure, although they also have some level of inaccuracy.

We can estimate resting metabolic rate with indirect calorimetry relatively easily if you have access to a service that provides it.

Indirect Caloriemetry machine in use

But outside of research settings, it is difficult to quantify total daily energy expenditure.

Just because we cannot easily track something does not mean it is not occurring.

If I ran 5km but did not track it perfectly, did it still happen? If I bench-pressed 100kg but did not know how much weight was on the bar, did it still happen?

The point I am getting at is:

  1. In most cases cannot track our intake or expenditure accurately.
  2. This does not invalidate the CICO model. It just means that if you are trying to influence your calorie intake or expenditure, you are basing your decisions on estimates.

If You Decrease Your Calorie Intake, Your Metabolic Rate Will Slow Down

If you decrease your calorie intake, your metabolic rate often does decrease a bit.

There are a few factors here.

One is the concept of metabolic adaptation.

Metabolic Adaptation Depiction

Your body compensates for lower calorie intake by downregulating certain functions and decreasing calorie expenditure.

This sounds scary. But it rarely accounts for more than a 200kcal decrease in energy expenditure.

It also goes in both directions. When you raise calories, calorie expenditure increases.

After as little as 4-weeks back at maintenance calories, metabolic adaptation is barely detectable anymore in most cases.

Another factor that comes into play is that as you lose weight, you physically get smaller. This can result in fewer calories being burned since smaller bodies require fewer calories to be maintained and moved around.

Once again though, all this is accounted for in the CICO model when you understand that both parts of the equation are not just static numbers.

What About People Who Don’t Lose Weight on Low Calories, but Start Losing Weight on Higher Calories?

In the real world, we see a lot of examples of this. We see people who were supposedly on low calories and not losing weight. And then when they tried a different approach, that was higher calorie comparatively, they started losing weight.

Does that not break the CICO model?

The first thing to address is the following: Why do we not ever see this occurring in research where all food is provided?

This is an important question to ask.

Surely some of these people would be incredibly fascinating case studies if this holds true in a controlled environment.

Every time a study is done where all the food is provided for participants, and low calories are involved, weight loss occurs.

This does not mean that low calories are a good idea. I am just highlighting that in controlled studies, this proposed issue does not exist.

In the real world, there are a few factors.

  1. Underreporting is incredibly common. There are so many reasons for this. But the research shows that almost everybody who is looking to lose weight reports a lower calorie consumption than their average intake actually is.
  2. What people say they are doing is often only a snapshot in time. It does not necessarily reflect their intake over a long period of time.
  3. Changing approaches or targeted calorie intake can improve consistency or adherence.
  4. In some cases, metabolic adaptation can play more of a role than others. This is particularly relevant for states of low energy availability. This only explains certain niche cases, and it is often in combination with other factors.
  5. Energy expenditure can change in the process of increasing calorie intake. It could be related to the changes in intake, or it could be unrelated.

There can be a long list of explanations. But that is why I think it is relevant to focus on the research where all food is provided and accounted for. Otherwise, it leaves a lot of room for speculation, and we can end up coming to the wrong conclusion simply due to a lack of information.

Practical Summary

Every criticism of the CICO model has a logical counterargument.

Most of these criticisms stem from looking at CICO as if it were a simple model based on static numbers.

But they are not static numbers.

Components of Energy Expenditure

If we change our calorie intake, it changes our calorie expenditure.

Our nutrition effects our hormones. And our hormones effect both our calorie intake and our calorie expenditure.

CICO is not a dietary approach. It is a model for understanding weight management.

Counting calories might not be an approach that works well for certain people.

But tracking calories =/= CICO.

It also does not mean “calories in vs calories out did not work.”

Whether we pay attention to it or not, CICO is always occurring.

Understanding the model is helpful even though we cannot perfectly measure either our intake or our expenditure. For those who pay closer attention to this, it can be helpful to use estimations to start off with, and then adjust over time based on what happens in practice.

But regardless of how you go about it, ideally you find an approach that works well for you and influences energy balance in the way you want it to overall, even if you do not focus on it.

By Aidan Muir

Aidan is a Brisbane based dietitian who prides himself on staying up-to-date with evidence-based approaches to dietetic intervention. He has long been interested in all things nutrition, particularly the effects of different dietary approaches on body composition and sports performance. Due to this passion, he has built up an extensive knowledge base and experience in multiple areas of nutrition and is able to help clients with a variety of conditions. One of Aidan’s main strengths is his ability to adapt plans based on the client's desires. By having such a thorough understanding of optimal nutrition for different situations he is able to develop detailed meal plans and guidance for clients that can contribute to improving the clients overall quality of life and performance. He offers services both in-person and online.