Calories In Calories Out (1 of 2)

(Versión en español: pinchar aquí)

The Calories In Calories Out theory

Authorities tell us that we can control our body weight by counting our intake of Calories and our energy expenditure. This is the so called Calories In Calories Out (CICO) theory.


They say that if we keep a caloric deficit we will lose weight. They even tell us how much weight we will lose:

«If you need to tip the balance scale in the direction of losing weight, keep in mind that it takes approximately 3,500 calories below your calorie needs to lose a pound of body fat. To lose about 1 to 2 pounds per week, you’ll need to reduce your caloric intake by 500—1000 calories per day». Centers for Disease Control and Prevention (government of the United States)

They even give us numbers: one pound less per 3,500 Calories deleted. How can this theory be wrong if they can give us the detailed amount of weight we will lose, as a function of the Caloric deficit we make?

The facts. What does experimental data say about the CICO theory?

In this scientific study one group of subjects kept a deficit of 500 Calories/day for the last 18 months of the study. That is an aggregate deficit of 270,000 Calories. According to the CICO paradigm they should have lost 77 pounds. They gained 4 pounds during those 18 months.

CICO theory says they should have lost 77 pounds, but instead they gained 4. You don’t believe me? Check the study and do the math yourself.

Let’s play nutritionists again and check another study. Again I show to you a comparison of a) what the CICO model says and b) the real weight loss (I borrow the data from Zoe Harcombe’s analysis of a 2014 study):


The CICO theory predicted a weight loss of 25-30 Kg after 12 months. Real weight loss was 2-5 Kg.

Are you still not convinced about the CICO model being useless? Ok. In another study, for 12 weeks group A ate 300 Cal/day more than group B, but their diets were different. Group A had an extra 25,000 Calories, and they lost 3 pounds more than group B at the end of the study.  25,000 more Calories eaten, 3 more pounds lost. The CICO theory says they should have lost 7 pounds less, not 3 pounds more.

How is this insanity even possible? nobody checked out the CICO model before making it public policy?

Why is the CICO theory so wrong? I tried to answer that question herehere, herehere and here, but I will try to give another perspective on the second part of this post. Dear CICO theory, «this will not be over quickly. You will not enjoy this. I am not your Queen!»

Homework: can you tell me how does an adipocyte (fat cell) know we are eating too much and doing little exercise, so it can decide to store fat instead of releasing it?

Reading further:

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