CICO: The Superficial Truism

"A long habit of not thinking a thing wrong, gives it a superficial appearance of being right, and raises at first a formidable outcry in defense of custom. But the tumult soon subsides. Time makes more converts than reason."

 - Thomas Paine

Summary:

The CICO model is an oversimplified, outdated interpretation of human metabolism that fails to account for hormonal, biochemical, and adaptive mechanisms that regulate weight and body composition. Relying on it leads to ineffective, sometimes damaging approaches to dieting and fat loss. The CICO model emphasizes the calorie, as measured in a bomb calorimeter, that does not reflect how the human body processes food. It ignores that macronutrients are metabolized and utilized differently, does not account for changes in intestinal microbiome, hormones, or nutrient usage. It is a reductionist model that appeals to ignorant "influences" and "gurus" because it does not require an understanding of human biological complexity, including adaptive thermogenesis, nutrient partitioning, hormonal responses and actions, and various confounding variables inherent in applying a linear model based on physics to the dynamic system of the human body.

There are many so-called truisms that infect and fester in the space of training and nutrition, and each of them deserves to be ripped out by the roots. Among the most pernicious and dogmatic of these is the tired mantra of “Calories in, Calories Out” recognized by its acronym, CICO (which I pronounce, “sicko” for reasons that will be made apparent later on). We are going to examine CICO first before digesting its flawed and reductionist nature.

Yes, that was a pun.

CICO asserts that the entirety of human metabolism is merely that of thermodynamics. In essence, our bodies are little more than fleshy steam engines. More specifically, advocates apply the first law of thermodynamics, Conservation of Energy, to humans. This law states that energy cannot be created or destroyed—only transformed from one form to another. Applied to human metabolism, this law would read: “Calories, or chemical energy, from food are converted into heat, mechanical work, or stored as fat.” Further simplified into popular “influencer” jargon, the assumption is that if you eat more calories than you burn, you gain weight; if you burn more than you eat, you lose weight. This same concept is where the “eat less, do more” mantra arose, a misguided and simplistic movement that has caused tremendous harm to those who believed that they were following tried and true wisdom.

To repeat, the “Calories In, Calories Out” (CICO) model posits that weight change is simply the result of calorie balance—burn more calories than you eat, and you’ll lose weight. Under this view, you can eat 2000 kcal per day of gummy bears and lose weight as long as you utilize 2100 kcal/day. 

Limitation 1: The Calorie

A “calorie” is not a unit of measurement for work or metabolic output. A calorie is actually a unit of measurement used in physics, and is the amount of energy needed to raise the temperature of 1 kilogram of water by 1°C. To measure the caloric content of food, it is incinerated in a sealed chamber. 

Your body is not a sealed chamber that incinerates organic material to produce energy.

At its very core, the calorie, which CICO depends on, is tremendously flawed. Calories embody the many weaknesses of CICO generally: it ignores the differences in how substrates are metabolized (carbohydrates, fats, and protein are all three digested different), ignores the effect of the microbiome, takes no consideration of the hormonal system, nutrient partition, or the use of the substrate in question. It does not consider the response of insulin, leptin, or ghrelin, whether or not fat is stored or oxidized, or whether muscle is built or catabolized. It also does not consider metabolic adaptation, either biologically through thermogenesis or psychologically through reduced energy output. This is sufficient argumentation against CICO, as it is merely fruit from the poisonous tree. Like the calorie itself, CICO is a reductionist view that ignores the complex biochemical, hormonal, and adaptive processes that regulate metabolism, energy expenditure, and body composition. 

Limitation 2: Adaptive Thermogenesis

There are instances where people are on hypocaloric diets but continue to gain body fat or “plateau” in their weight loss. Following CICO, these individuals continue to “move more, eat less” until, in some cases, they are at extremely low food intake. But why do these people have to continually eat less and less to lose weight to begin with?

The human body is a complex organism designed to survive. To these ends, if food intake is reduced, the body adjusts its energy expenditure to account for caloric restriction by reducing basal metabolic rate and non-exercise activity thermogenesis. This is true even in the short-term, confounding the assumptions of weight loss CICO assumes. CICO advocates insist that these plateaus exist only because individuals “miscount” calories, but this is simply not the case: plateaus are due to adaptive thermogenesis, a mechanism essential to mammalian survival in the event of decreased food availability.

Aside from biological adaptations, CICO also discounts human nature. Individuals placed on a hypocaloric diet tend to react by reducing their energy output, or by spontaneous snacking, or even increases in sleeping (prior to endocrine disruption). This is a natural mechanism that responds to decreased energy intake by decreasing energy output in the form of spontaneous movement, walking, and even fidgeting. Psychologically, those on hypocaloric diets are also less prone to exercise or engage in other physical activities, and generally have less willpower than those who are eating sufficiently.

Limitation 3: Nutrient Partitioning

 Even with perfect, neutral energy intake, different macronutrients and hormonal responses direct how the body uses or stores calories. A “calorie” of protein is not the same as fat or carbohydrate. 

Nutrient partitioning is one of those areas of nutritional thought that should be a part of that mysterious “common sense” sphere. It is made obvious through the following challenge which I have presented to numerous disciples of SICO of which none have accepted: maintain your same calorie count entirely in gummy bears.

I am still looking for takers.

The Influencer Counting "Calories"

For the adults in the room, nutrients are different and are otherwise metabolized differently and utilized differently by the body. Nutrient partitioning is even more necessary in hypocaloric diets, with protein being utilized as a larger percentage in order to maintain or even grow muscle mass depending on the physical training involved. With sufficient protein, fat loss represents a greater percentage of total weight loss, proving irrefutably that nutrient partitioning is a very real and meaningful phenomenon.

Nutrient partitioning also directly affects whether or not nutrients are used or stored. Nutrient-sensing pathways and gene expression determine whether or not substrates are utilized or stored regardless of current caloric condition. Moreover, hormones like leptin, ghrelin, insulin, and cortisol mediate hunger, satiety, fat storage, and nutrient oxidation—regardless of calories consumed. Feedback loops, regulatory hormones, and cellular signaling define human metabolism as a nonlinear function, contrary to what CICO advocates. Nutrient-sensing pathways, like TOR and AMPK, respond to nutrient type and availability, not just caloric quantity. Even males of identical caloric content can have tremendously different effects depending on food substrates; excess calories from carbohydrates and fats have different outcomes, especially in populations with dysregulated sugar and metabolic disease.

Limitation 4: Hormonal Effects

The role of hormones in nutrient partitioning and metabolism more broadly cannot be overstated. Low-calorie diets increase cortisol production, as well as impacting the thyroid gland to such an extent that it mirrors sick euthyroid syndrome. Elevated cortisol levels can lead to dysregulated blood sugar metabolism, which can contribute to fat storage, particularly around the abdomen. A stress hormone, cortisol increases blood glucose levels by drawing glucose from glycogen stores in the liver and muscles. If this glucose is not utilized through physical activity, insulin is then secreted to return blood glucose levels to normal by storing the glucose, a circular process of perpetual fat accumulation. Dysregulation of the thyroid, like that caused by hypocaloric diets, also perpetuate a self-defeating weight loss programs by reducing triiodothyronine (T3) and increasing reverse T3 (rT3), which can slow down metabolism and reduce energy expenditure as an adaptive response to hypocaloric dieting. Even stored fat tissue experiences hormonal remodeling in response to hypocaloric dieting that decreases the use of fat for fuel and emphasizes energy storage.

Insulin, too, is integral to nutrient partitioning. High insulin levels, like those found in metabolic disorder and high-carbohydrate meals, can promote fat retention even during calorie restriction by impairing lipid oxidation and favoring energy conservation. Leptin resistance accomplishes much the same and often runs in tandem with insulin resistance. In general, hormonal responses to calorie deficits include reductions in leptin, thyroid hormone (T3), testosterone, and increases in ghrelin — all of which contribute to fat conservation specifically. Under adaptive thermogenesis, the body slows muscle turnover and prioritizes fat storage when exposed to hypocaloric dieting. Through neurohormonal means, hypocaloric dieting primes the body to restore lost body fat in the post-diet era, explaining one side of the dreaded “yo-yo” dieting phenomenon.

Thus, following the tents of CICO align individuals to fail on a number of fronts, all while shaming or judging individuals for failing on a CICO-oriented weight management approach. It is a flawed, reductionist theory that is easily disproved and discounted. That it persists as the core of weight management approaches explains at least in-part why the industrialized world struggles with obesity and increasing rates

The Solution

The CICO model, while useful for a surface-level understanding, is biologically incomplete. It fails to account for how nutrient type, metabolic adaptation, hormonal feedback, and nutrient partitioning influence body composition and health outcomes. A more sophisticated framework incorporating hormonal regulation and nutrient signaling pathways offers better insight into weight management and metabolic health. This is the model that nutrition plans created by Ulfhednar Training Systems are based upon.

Under this model, CICO is rejected with a holistic model that prioritizes nutrient density and the biological use of energy substrates. By acknowledging what purposes our body uses different substrates we can better align our diet to satisfy our biological needs without inducing the negative consequences and poor outcomes that follow CICO diets. Combining nutrient timing and content to leverage specific hormonal responses is made all the easier, and combined with an intelligent training and optional supplement protocol, we can build long-lasting diets that are enjoyable and help us maintain a healthy weight. This is true regardless of goal, be it health, weight gain, bodybuilding, strength training, endurance sports, or any other purpose.

It is time for CICO to be cast away alongside other misleading claims in physical fitness and nutrition, from the "morph" theory to meal plans based on blood type. Meal plans that incorporate the many biological systems inherent in the human body are only now being studied in the mainstream but have long been the foundation of dietary protocols that I have been designing for more than a decade.