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Ending the CICO debate

Updated: Jun 3, 2022

CICO or Calories In, Calories Out, is a concept in nutritional science that is used to explain how weight loss happens. It is also one of the most debated topics in the fitness industry. I do not know where it started but people started to refute the validity of CICO for likes shares, follows, and subscriber counts. In this article we will understand CICO and will debunk the arguments used to invalidate CICO.

I think the biggest strife with CICO is because people think it's Calories In Calories out, which is different from Calories In, Calories Out.

Although in my humble opinion this must be written in the Thermodynamically correct form, i.e., Calories In - Calories Out

That is Calories In (Minus) Calories Out.

According to Thermodynamics :

  • when Calories In - Calories Out = 0, no change in the state of the system is observed

  • when Calories In - Calories Out > 0, There's a net inflow, or storage of energy within the system.

  • when Calories In - Calories Out < 0, There's a net outflow of energy from the system, and the system loses energy.

When people write CICO as Calories In Calories Out, they get confused. I Think what they read it as The amount of calories ingested is the amount of calories spent. Which is not what it is. CICO talks about energy balance, not about conduction of energy.

So, to be clear Calories In, Calories Out is read when Calories ingested are (greater than, less than) Calories Out we (gain/lose) weight respectively.

"Classical the only physical theory of universal content concerning which I am convinced that, within the framework of applicability of its basic concepts, will never be overthrown" - Albert Einstein

Let us now see how weight loss works with CICO.

When you reduce the amount of calories you consume your body responds by:

  1. Initially dropping weight

  2. Then it adapts to the reduced energy intake in three ways

    • It becomes more efficient at functioning with reduced calories intake, thus reducing the calories that you burn during the day, compared to when you were eating normally.

    • It also creates new fat cells to prepare for storage when the food intake does return to normal.

    • The hormonal milieu in the body shifts to favor fat gain, such as lowered thyroid, insulin resistance etc.

So when you are ready to go back to eating normally after dieting your body is more primed to store more fat and spend less energy, this is why most people who lose weight using crash diets, juice diets etc. gain back all their weight and more in a short period of time.

Most people think of it as failure of Thermodynamics, when it really is just the body's adaptation to new energy balance.

Why then some people claim that it's not all about CICO? They don't because, it gives them something to do. People want something to demonize, and a cure to kill that demon, case in point, no fat diet, low carb diet because carbs and fats are such bad things.

When people go on different diets, such as IF, or low fat, low carb diet they are essentially restricting either the time in which they can eat, or they are limiting the food that they can eat. Either way you're enforcing some sort of restriction. There's not a single person who can eat in 6 hours as much food as they eat in 24 hours, similarly you cannot have any of the macro-nutrient at the exclusion of others without saturating your receptors for that nutrient, thus limiting the amount of food you can eat.

In case of protein, after a big protein meal your amino acid reserves are topped off, you won't feel hunger till the amino acid reserves are running low, again limiting how often you can eat thus inducing calorie restriction. Also protein has a high thermic effect, i.e., the energy required to digest protein is very high compared to energy derived from it. Thus increasing energy expenditure at rest.

This induced calorie deficit is what drives the weight loss.

Why do some people don't agree to CICO paradigm. That is because they have never tracked their their calorie input vs calorie output. If they start doing so all of their questions about hormonal issues, biology being too complex for thermodynamics will be answered.

How to employ CICO for fat loss?

It is fairly simple but it requires a degree of work, at least for the first few weeks. All you have to do is, track your calories intake for at least 7 days consistently, and take average of the calories consumed in those 7 days. This will give you a baseline calorie expenditure for your body at rest, this is called BMR or Basal Metabolic Rate. Multiply this number by your activity factor as given in the table given below.

Activity Level

Activity Factor



Light Activity


Moderate Acitivity


Very Active


Extra Active


Where the activity levels are defined as

  • Sedentary - You have a desk job and you don't exercise.

  • Light Activity - Either you exercise and have a desk job, or you have a job that requires you to be on your feet (salesman, nurse, etc.).

  • Moderate Activity - Intense training + desk job, or Moderate Training + a job that keeps you on your feet, or don't work out but have a very physically demanding job (construction crew, ironsmith etc.)

  • Very active - Hard training on most days + a job that requires you to be on your feet.

  • Extra active - Weight Training in the AM + Cardio, or second weight training session in the PM+ plus a physically demanding job.

The resultant of BMR*Activity Factor is your calorie output. Now if you want to lose fat you must consume less calories than the calorie output which you can ascertain by tracking as before.

Tracking calories will make you more aware of the content of the food that you consume thus informing your food choices in the future, helping you make healthier food choices. This is also important for the long term success of your diet, as you will be able to modify your existing diet to fit the required calories to achieve the negative calorie balance and thus initiate fat loss.

However, as mentioned previously prolonged calories restriction can cause certain adaptation which will stall the fat loss unless you reduce calories further. This is hardly a sustainable approach. Therefore, you need to increase the activity level so that overtime you can eat more and still be in a negative calorie balance to continue to lose fat.

Simple ways to increase daily activity level

Walk more - Walk as much as possible, take a walk to the grocery store, get off a stop earlier to walk rest of the way home, walk your dog rather than having someone else do that for you, walk 10-15min after each meal, walk while you talk on phone.

Do household chores - Wash your car by hand, rake the garden, mow your lawn, do laundry by hands a couple of times a week, use a snow shovel.

Other ways to increase physical activities

  • Play with your kids

  • Explore new things to do that has a physical activity component

  • Join a cycling club

  • Dance to music when you can

This is not an exhaustive list, a simple Google search will yield several links that you might be interested in exploring. Find a hobby or few that you are interested in and can partake in regularly. Rinse & Repeat.

Hopefully this article shed some light on the CICO paradigm and how to use it. If you think this article helped solve some doubts around weight loss than help the blog by sharing this with your friends. Thanks for reading.

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