CICO: The Science-Based Truth You Need to Know

November 16th, 2017|Fat Loss, Nutrition|
CICO - Myolean Fitness

If you’ve been unlucky enough to have stumbled upon pretty much any of the recent internet articles on CICO (Calories In, Calories Out), then you may have read that:

  • CICO is a recent diet fad
  • CICO is a weight loss diet that’s disastrous for your health
  • CICO is about eating cake and pop-tarts
  • CICO is about counting calories
  • CICO doesn’t work for weight loss because “not all calories are created equal” or because “a calorie is not a calorie”
  • * insert any other silliness you may have read here

As you may have already figured out, the above is mostly just nonsense. Worry not, however, since, we are set on clearing up some of the confusion around the topic of CICO.

So, in this article, we’ll talk about:

  • why CICO isn’t a “diet” or a “recent fad”,
  • what CICO really is,
  • why a calorie is a calorie (sort of),
  • why a calorie isn’t a calorie (sort of),
  • whether you need to count calories with CICO, and
  • what you should really be doing for fat loss.

Here goes!

What CICO is (and what it’s not)

Firstly, here’s what CICO (which stands for Calories In, Calories Out) is definitely not: a diet or a dietary approach.

Instead, CICO is meant to represent the idea that the energy that goes into the body minus the energy that comes out of the body, equals the change in the body’s energy stores.

CICO - Myolean Fitness - Energy Balance Equation

This is, of course, merely a rehash of the First Law of Thermodynamics, which states that when energy passes, as work, as heat, or with matter, into or out from a system, the system’s internal energy changes in accord with the law of conservation of energy.

An important thing to note from the above description is the word “law”. Not “theory” or “hypothesis” or “belief”, but LAW.

Following from the above, it’s relatively straightforward to understand why CICO isn’t really a recent thing. Since the laws of physics always have and always will apply, then CICO is also a timeless idea. Consequently, like with gravity, you also can’t really choose if you want to follow CICO or not. You are bound by the laws of physics as is everyone else.

Take home point: CICO is not really a diet, but, instead, a simple restatement of the energy balance equation and, as such, is also timeless and mandatory.

So CICO is just about calories then, right?

Well, sort of but not really.

Again CICO is not a diet and, consequently, doesn’t really make any recommendations with regards to food selection or quality. Instead, it merely explains what happens to the energy stores of a system as a result of imbalances between the net intakes and net outputs that are taking place.

So although you don’t get to choose whether CICO applies to you or not (it does), you can certainly choose how you’ll go about your diet in terms of food selection and timing in order to achieve your goals.

What this means is that you have a choice of using:

  • a ketogenic diet,
  • a high carb/low fat diet,
  • a moderate carb/moderate fat diet,
  • calorie counting,
  • macronutrient counting, a.k.a IIFYM (If It Fits Your Macros),
  • intermittent fasting,
  • alternate day fasting,
  • a paleo diet,

or any other dieting approach you prefer in order to lose fat (or even gain fat).

Remember, however, that whatever dieting approach you choose, you’re still doing CICO because CICO always applies to everyone at all times.

CICO - How Fat Loss Diets Work - Myolean Fitness

As you can see in the infographic above, all diets can work for fat loss, provided that they help the dieter achieve a negative caloric balance between intake and output (i.e. a caloric deficit). This, of course, doesn’t mean that the food choices you make don’t matter for health and body composition, since calories from different foods will have different effects on your body.

Take home point: Since CICO is merely meant to explain what happens to the energy stores of a system, it isn’t a diet and it doesn’t give food selection recommendations. This doesn’t mean that it’s just about calories, as food quality matters for health, performance and body composition.

Aha! So a calorie isn’t a calorie!

Well, yes and no.

Remember, a calorie is a measurement unit of heat or energy. Since, in its simplest definition, a food calorie (1 kcal) is the amount of energy needed to raise 1 kg of water from 15 to 16 °C, then, from a thermodynamic point of view, a calorie is, of course, a calorie.

However, things get a little more complicated when it comes to the human body, as:

  1. the energy released from the combustion of food in a calorimeter is not always identical to the energy available to the body from eating that food,
  2. different foods with the same caloric content can have varying amounts of metabolizable (or usable) energy,
  3. different foods can differentially affect energy intake, and
  4. different foods can differentially affect energy expenditure.

However, the implication from the above isn’t that a calorie isn’t a calorie, but that the source of the calories can affect their metabolizable energy, as well as the two sides of the energy balance equation.

Of course, since CICO is about energy balance, it takes all the above into account.

CICO - A calorie is not a calorie - Myolean Fitness

Let’s reiterate to make this point crystal clear:

We KNOW that the body is not a “perfect engine” and that the energy liberated from the combustion of food is not always exactly identical to the energy available to the body from the consumption of that food and we KNOW that foods with identical energy contents provide varying amounts of actual metabolizable energy to the body. These “errors”, however, don’t mean that the laws of thermodynamics are “broken” and that CICO doesn’t apply. Instead, they suggest that we have a limited ability to determine exactly how much metabolizable energy a given diet contains.

– We KNOW that the thermic effect of different foods and macronutrients varies. As we’ve talked about before, the thermic effect of protein is around 20-30%, that of carbohydrates is around 5% and the thermic effect of fats is usually close to 0%. Again, all of these are part of CICO.

– We KNOW that that different foods can have differential effects on hunger and satiety and, consequently, affect energy intake. We’ve also discussed this in another article. Foods that are rich in protein and/or fiber and/or water tend to be more satiating. There is also research which suggests that ketogenic diets may have independent effects on satiety. As you will have guessed, these are taken into account by CICO.

Take home point: From a thermodynamic point of view, a calorie is a calorie. However, calories from different food sources can provide different amounts of metabolizable energy to the body and can have different effects on our energy intake and output. This doesn’t mean that the laws of thermodynamics are broken and that CICO doesn’t work, since CICO takes all the above into account.

Online Coaching Side Widget within text 2 - Myolean Fitness

But CICO is still about counting calories, right?

Not really.

Whether you prefer to count calories or not is entirely up to you. Again, CICO merely explains how the energy balance equation works. It doesn’t make recommendations regarding how to go about your diet, including whether you should track energy intake or not.

However, not counting calories, doesn’t mean that CICO won’t apply to you. Think of it like closing your eyes. The fact that you can’t see the world around you doesn’t mean that it’s not there anymore and that all your problems are gone. Similarly, keeping your eyes open doesn’t mean that you will necessarily make great decisions in life.

Should you count calories?

Well, we can’t give you an answer to this question that definitely applies to you, but we can help you figure it out on your own with a little Facebook post that we made some time ago about this very topic. Check it out, below:

CICO - Counting Calories - Myolean Fitness

Take home point: CICO doesn’t make recommendations regarding how to go about your diet, including whether you should track calories or not – that’s entirely up to you. However, not counting calories doesn’t mean calories don’t count.

What to take away from this article

With the above said, here are the main points that we want you to take away from this article:

  • CICO is not a diet, let alone a recent diet “fad”. It’s simply a restatement of the energy balance equation. It always has and always will apply to everyone.
  • CICO is not about counting calories. You can lose or gain fat without ever counting a single calorie. Calories count but you don’t have to count them.
  • CICO is neither “healthy” nor “unhealthy” because it’s not a diet and because it simply doesn’t make any specific dietary recommendations. Whether you make healthy dietary choices or not is up to you.
  • A calorie is a calorie from a thermodynamic point of view.
  • The quality of the foods where the calories are coming from matters for body composition, health, energy levels, etc. This doesn’t go against CICO and the laws of thermodynamics, nor does it mean that a calorie is not a calorie.
  • All diets work for fat loss, provided that they allow you to eat fewer calories than you expend consistently over time.

What we recommend for fat loss

Also, as we’ve mentioned before, if you want to lose weight and fat, we recommend that you find a dietary approach which:

  1. helps you create a large enough caloric deficit for a sensible rate of fat loss,
  2. is comprised primarily of a variety of minimally-processed, micronutrient dense foods,
  3. provides enough protein to prevent losses in lean body mass and to help with satiety,
  4. honors your individual preferences with regards to meal timing, food choice, and so on,
  5. can be adhered to in the long term, and
  6. promotes a healthy relationship with food.

What next?

If you are a fellow evidence-based fitness professional and are also annoyed about all the nonsense articles on the internet regarding CICO, please share this post. The more people we reach, the better.

If you are not a fitness professional but you’ve found this article to be informative and helpful, please show your support by sharing it with your friends.

Also, if you want to learn more about fat and weight loss, we highly recommend that you check out the following posts:

 Share this on Facebook and join the conversation

Subscribe to our FREE newsletter

Before you go, make sure that you grab a copy of our fat loss e-book: “9-Step Guide to Permanent Fat Loss” by subscribing to our FREE newsletter!

Myolean Fitness - 9-Step Guide to Permanent Fat Loss


  1. Viktor 14/03/2018 at 7:32 pm - Reply

    Thanks for this clear and well-structured article.

    Finally people are saying that CICO is NOT dietary advice! But just a variation of energy conservation. Real dietary advice has to be found elsewhere.

    What I still don’t get is: Why is CICO useful? What do we gain from it?

    As I understand from your article, weight loss is equal to caloric deficit. Then, why don’t you change your info graphic text from “By creating a caloric deficit” to “By making people loose weight”?

    • Myolean Fitness 14/03/2018 at 8:13 pm - Reply

      Thanks for your comment Viktor,

      CICO is useful in that:

      1. It identifies what we must achieve to lose fat: an imbalance between energy intake and output. As strange as it may sound, many people are unaware of this and will try every “trick” in the book to lose fat except than to try to sustain a hypocaloric diet. Seriously, join any weight loss forum and you’ll keep seeing people ask about Apple Cider Vinegar, Bullteproof Coffee, waist trainers, supposed fat burning supplements, and a million other things. None of them have simply tried to monitor their caloric intake, though… It’s always about that one new trick – i.e. silly distractions.

      2. when you delve into it, it aims to describe how different foods can affect satiety, energy levels, thermogenesis, energy intake and output. For example, protein is much more thermogenic than fats. CICO actually describes this, even though most people are unaware that it does. In describing how different parts of the energy balance equation can affect one another, it helps make sense of what a good plan of action is for losing fat.

      I hope I’m making sense 🙂

      • Viktor 15/03/2018 at 1:14 pm - Reply

        I think I understand it now.

        I wasn’t considering your point of view because I’ve done intensive research on weight loss, hormones and dieting for over a year. And it didn’t cross my mind that people might not know the fact of energy conservation and that weight loss is equal to taking less food in than you excrete or burn.

        I think the concept of calories and CICO still has major flaws, which you also address in your article.

        You say correctly that the body’s response to different nutrients is different despite having the same amount of calories. This is complicated even more by adding stuff like fiber and vinegar that further change the metabolic response.

        You clearly state that CICO is independent from healthy-unhealthy. This is an important point. There was this professor who lost weight on the “Twinkie Diet” by obviously producing a caloric imbalance. But no sane person would recommend this diet. 🙂

        And the biggest flaw is the calories-out part. Unless you are strapped in a special device, you can’t really know how much calories you are burning. There are of course estimates, but they don’t take into account what your body actually does. The only way for a normal person to check if she is eating less calories than she burns, is to wait until she looses weight.

        Now, having ranted about the flaws of calories and CICO, I think it is still the best concept we have, in particular for beginners.

        I mean, how else can we quantify the amount of food and the amount of energy expenditure.

        Despite its flaws, I can’t think of a better concept to teach beginners. If a person comes to me and says “I have no idea about nutrition, hormones, fitness. Please give me advice on how to loose weight but only in 3 sentences.”. I would say exactly what you say: “See, that you don’t overeat in calories. Eat plenty of green-ish vegetables. Try to avoid sugar and sugary drinks.”

        But, the more people know about nutrition, the more we have to walk away from CICO. We should say: “Yes, CICO is a fundamental truth, but here is a list of equally important aspects: …”

        CICO should be the first, but definitely not the last words in nutrition and health.

        • Myolean Fitness 15/03/2018 at 1:33 pm - Reply

          Yep! In fact, I would go as far as to say that MOST people don’t know that fat loss is the result of a caloric deficit! Try this experiment: ask friends/family members who are not educated on nutrition this question: “What causes fat gain”. I would bet that most people will respond with things like sugar, fat, eating late at night, eating carbs, not drinking enough water, a low metabolic rate, and so on.

          Regarding the flaws of CICO, I don’t really consider the things mentioned in the article as flaws per se, since CICO takes these things into account. The problem is that people are unaware that CICO takes these into account! 🙂

          I agree with you that it’s practically impossible to estimate our energy intake and expenditure with any accuracy (unless we were subjects of a metabolic ward study), which is why we try to roughly estimate our clients’ energy expenditure, set a deficit, and then monitor progress so we can adjust accordingly! 🙂

          Regarding other things being equally important as CICO and that CICO shouldn’t be the last words in nutrition and health, I absolutely agree! As mentioned in the last part of this article:

          “…if you want to lose weight and fat, we recommend that you find a dietary approach which:

          1. helps you create a large enough caloric deficit for a sensible rate of fat loss,
          2. is comprised primarily of a variety of minimally-processed, micronutrient dense foods,
          3. provides enough protein to prevent losses in lean body mass and to help with satiety,
          4. honors your individual preferences with regards to meal timing, food choice, and so on,
          5. can be adhered to in the long term, and
          6. promotes a healthy relationship with food.”

  2. Bob 17/05/2018 at 8:29 pm - Reply

    The First Law of Thermodynamics applies to a closed system. The human body is not a closed system. What about BMR? Its not a static number. It changes, all the time. If you are on a 2,000 calorie a day diet, and reduce your calories to 1,500 you BMR will reduce by about 25%. Same thing in reverse, it you increase your calories to 2,500 your BMR will also increase by about 25%. Thats why CICO doesnt work for weight loss. Maybe short term you will see some, but as the BMR adjusts to the new input, then that weight will come back.

    • Myolean 17/05/2018 at 10:46 pm - Reply

      Hello Bob and thanks for your comment.

      Unfortunately, the source of information you have provided (Jason Fung’s blog) isn’t a very good source of nutrition information, as Jason often cherry picks research and miscommunicates it in order to give support to his claims. It’s no surprise that the vast majority of the scientific community doesn’t take him seriously.

      I would highly encourage you to give this a read, by the way, as you seem to have formed some opinions about CICO that may not hold true:

      Thanks again for your comment and best of luck in your fitness journey! 🙂

Leave A Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.