*CI=CO is a simple description of the first law of thermodynamics (conservation of energy), this refers to the fact that energy cannot be made or destroyed only transferred. So if a certain amount of energy is inserted into an organism the same amount of energy must be extracted from the organism, altho the energy doesn't have to leave in its original form.
*CI=CO can be written as:
Chemical energy in (food) = heat energy, kinetic energy, chemical energy (stool), electrical energy out.
(there might be other forms of energy we excrete that I have missed)
The basic premise of the equation is that what you do to one side you must do to the other, for it to balance. If I go for a run, I have increased the amount of kinetic and heat energy I have expended therefore I MUST add to the chemical energy going into the system by eating or fat tissue release, as the first law states. We can balance the equation more than one way, this is shown below:
First tell me if any of the following equations don't add up.
5-2 = 5-2
(5-2) + 1 = 5-1
There all good hey. lets get tricky, lets substitute numbers for energy. lets say that 5 equals calories in, it also must equal calories out.
5=5 is written from: CI=CO
now let us say that -2 equals a calorie deficit and +2 is a directly proportional amount of energy from your fat reserves.
(5-2)+2=5 written from: CI - cal deficit + fat released = CO
This is the bog standard way to blast fat in the dieting world, as we can see it is a true statement. You could have also added more energy expenditure (going for a run) for an unchanged calorie intake and the equation would still have to add fat from stores to balance.
here's where it gets complicated. lets take that same calorie (energy) deficit written as -2 and add it purely to the equation.
5-2=5-2 written from: CI - energy deficit = CO - energy deficit
Whoa what just happened here. Someone added a calorie deficit to their diet but no fat was needed or lost, all that happened was energy expenditure was reduced by an equal amount. hmmm interesting.
finally lets still use our large calorie deficit written as -2 and add in a little from fat stores (+1) and also add in a little reduction in energy expended (-1)
(5-2)+1=5-1 written from CI - cal deficit + half fat released = CO - energy expenditure reduction.
So from the above equations all balanced and mathematically valid, we have organisms losing a directly proportional amount of fat to their calorie restriction, right down to losing no fat at all after calorie restriction, and as we seen with the last equation fat loss can also vary depending on the energy expenditure restriction. What does this all mean?
Well it means that CICO is not a fat loss strategy (it doesn't always lose fat) it is a description of energy use in the body. It is also clear to see why great big debates rage on internet forums and blogs the world over whether CICO works or not, in a fat loss argument, BOTH SIDES ARE RIGHT, you can lose fat and you can also lose no fat.
Also how do we determine if we are going to lose fat or not, I mean can't we just eat less and/or exercise more to force our bodies to delve into those fat reserves, well yes we can, BUT..... our bodies have options (god bless our evolutionary backup mechanisms) to balance the CICO equation, you might force a calorie deficit, but your body might respond with a metabolic down regulation (it is a valid energy conserving mechanism you know).
The above statement was specifically clear with a fellow MDA dieter (whom I gave some advice) whom after doing a calorie deficit for a few months (and successfully knocking a few pounds off), was complaining of reduced fat loss progress and low energy, lethargy, reduced metabolism and a reduced sex drive. It is plainly clear to see what has happened after keeping in mind the equations from above. he first used (5-2)+2=5 (full fat loss) then his body slowly introduced (5-2)+1=5-1 (a little metabolic down reg, a little fat loss) then he finally ended up on 5-2=5-2 (full metabolic down regulation). The really funny thing about that thread was most of the advice given was to keep the same calorie deficit but for him to increase his carbs ??????????????