The Calories In-Calories Out (CI-CO) Fallacy
CI-CO is the argument heard most when people say, "I eat well and workout a lot yet can't shift weight": people suspect I am a liar because science behind the law of thermodynamics is simple, complete and irrefutable. There is not a “Law of Thermodynamics” but four. Since people aren’t concerning themselves with the entropy of a crystal at absolute zero, let us assume they are referring to the first law. It can be reasonably assumed that they are parroting something they heard from someone else; possibly medical school, where they are also told that 50% of what they hear will either change or is simply ‘untrue’.
The first law states that in a thermodynamic process the increment in the internal energy of a system is equal to the increment of heat supplied to the system, minus the increment of work done by the system on its surroundings. It is often simplified to “energy can neither be created nor destroyed only transformed or transferred”. I do not disagree with that law but note: “In a thermodynamic process…”; this is a gross misrepresentation of the human body as a perfect thermodynamic process.
Consider four issues:
Issue 1: The assumption that there is no option for calories other than to be burned or stored
Carbohydrates basically work that way. Fats and proteins have other jobs to perform on the body. Protein does everything from building muscle cells to repairing cell membranes. Fat transports non-water-soluble nutrients, insulates neurons, and can be used to repair cell membranes. Fat and protein can be broken down and recombined into whatever the body needs. Eat a steak and your body might use it to make a cell membrane; Alfredo sauce might be used to produce insulate neurons in the brain. Fat and protein are to the body what wood is to us; burn it for fuel, build a house with it or turn it into paper. In any event, calories in the proteins and fats used in this manner are neither burned nor stored. The first hole in CI-CO.
Issue 2: The assertion that Basal Metabolic Rate (BMR) is Easily Predictable and Stable
Your BMR is the number of calories you would need to stay alive for 24 hours if you spent the day still and in bed; it is what would be required for breathing, heart rate, etc. It is typically calculated using the Harris-Benedict equation. James Harris was a botanist who freely admitted that his equation failed to take into account large amounts of muscle mass or the additional calories provided by excess body fat and that it was thus much more effective for individuals at, or very close to, ideal body weight. It is well documented that BMR responds to decreased caloric intake by slowing down. So if two friends have the exact same Harris-Benedict score, but one has been dieting, then the dieter will actually burn less calories at rest than his friend. Said another way, if these two friends eat the same number of calories in excess of their BMR score, the dieter will gain more weight than the non-dieter. Again, in this case CI-CO can’t hold up.
Issue 3: The requirement that the body be a perfectly efficient calorie burning machine
The Second Law of Thermodynamics explains entropy which only applies in a closed system: the human body is not closed. [The first law also applies to a closed system and, as such, people who think the first law applies to the human body would have a difficult time weaseling out of saying the second law applies.] The Second Law dates back to the mid-1800’s and explains the efficiencies of a closed system: it basically says it is impossible to create a system that has perfect efficiency of energy conversion, as there are always some losses in the conversion process. The maximum possible efficiency is different than the observed efficiency. Over time, entropy increases and a system becomes more disordered and less efficient. Early in the developing science of thermodynamics, researchers realized that while work could be converted completely into heat, the converse is never true for a cyclic process. “Certain natural processes were also observed always to proceed in a certain direction” (e.g. heat always moves from hot to cold). A machine that converts heat from a warm body into work, without losing heat to a cooler body, would violate the second law of thermodynamics. The Second Law is why physicists know that a perpetual motion machine is impossible (and not so simple, either). CI-CO cannot explain human metabolism or much else human.
The human body is even more complicated because ability to burn/store/use nutrients is affected by genetics, environment, hormones, previous caloric restriction and subsequent reduction in BMR, hydration level, chemicals etc. Calories eaten and calories used in voluntary movement are only two small parts of energy balance and, unless all other countless, wildly varying variables (internal and external) are controlled they are meaningless by themselves. As with metabolism, such variables never can be controlled as they are involved in affecting the efficiencies of a system over which we have no control.
Issue 4: For long term weight loss using this theory, then we’d have to eventually turn to starvation
If we wanted to use CI-CO effectively, knowing what we now know about entropy and how decrease in caloric intake causes decreased basal metabolic rate, we would just have to keep decreasing our calories and increasing our exercise until eventually we would be following disordered eating patterns. It would be the only way to stay under our ever plummeting BMR and eat less than we burn. Perhaps this is why 95% of intentional weight loss efforts fail. The body releases weight at first but then the damn science catches up to us and no matter how hard the people who’ve attended a physics amateur hour try to yell to the contrary, they will never be able to out-science the actual laws of thermodynamics and the complicated human body (which is not a lawnmower).
"Thermodynamics tells us nothing about why people do anything".
Bonus: Then there is the friend who eats everything in sight, does no exercise and never gains weight
Everyone knows somebody like this. I have a number of friends who eat way more than I do, exercise less and stay stick thin. Why do these people get to credit their metabolism but I’m just a fat, lazy, excuse-making slob if I suggest that my metabolism may be as slow as theirs is fast? So next time somebody tells you that it’s just CI-CO, consider telling them that you’ll be happy to talk to them about it once they have recited the laws of thermodynamics, defined the Harris-Benedict Equation, then discussed its specific limitations and explained to you how your friend who eats a ton and simply doesn’t gain weight.
Balance in an open system, like the human body, is when all energy going into the system equals all energy leaving the system plus the storage of energy within the system. But energy in any thermodynamic system includes kinetic energy, potential energy, internal energy, and flow energy, as well as heat and work processes. In other words, in real life, balancing energy includes a lot more than just the calories we eat and the calories we burn according to exercise charts. The energy parts of the equation include: calories consumed; calories converted to energy and used in involuntary movement; calories used for heat generation and in response to external environmental exposures and temperatures; calories used with inflammatory and infectious processes; calories used in growth, tissue restoration and numerous metabolic processes; calories used in voluntary movement; calories not absorbed in the digestive tract and matter expelled; calories stored as fat, and fat converted in the liver to glucose; and more. Add to that, to put it simply, each variable affects the others, varies with mass and age, involves complex hormonal and enzyme regulatory influences, and differs in efficiency. CI-CO applied to human metabolism tells neither doctors, nor us, anything about weight management.