Calories In – Calories Out

Calorie counting is one of, if not the, most widespread method used by people attempting to lose weight. It builds on the idea of CICO: Calories In – Calories Out. CICO is based on the thermodynamic principle that energy can neither be created nor destroyed. The consideration is that any energy we consume must either be expended or stored in our bodies. What’s more, we can store energy as fat, which can increase or decrease our weight. Thus, the differential between daily calories consumed and daily calories expended is the only thing that determines whether we lose or gain weight.

Should we consume more than we need, the surplus in chemical energy will be stored as fat. Inversely, should consume less than we need, our body will break down previously accrued fat stores to make up for the energy deficit.

The practical advice based upon the CICO principle to anyone trying to lose or gain weight is that they simply need to keep track or their daily caloric intake and adjust it up or down. If you desire to lose weight, simply lower your caloric intake, until the pounds start to drop and if you want to gain weight simply increase caloric intake until your weight goes up.

Despite the theoretical validity of CICO, in practice it has some significant issues. For one, it assumes that our bodies are capable of extracting 100% of the energy contained in a food, as if we were a bomb-calorimeter. This is, however, not the case. Multiple studies, including a 2009 study by Veldhorst et al., have found that changing the dietary composition can influence how much energy our bodies spend on digestion, absorption and metabolism of foods consumed, a concept know as the thermic effect.

Furthermore, CICO does not consider how the food we eat may affect other caloric expenditure not directly linked to the thermic effect. It assumes that, for the same body and activity level, your daily expenditure will be the same, regardless of what kinds of foods you consume. This has, however, never been verified. For example, at the same activity levels, a diet rich in protein may cause the body to expend more energy on muscle synthesis and repair, as excess protein is available. In comparison, a diet with no protein will certainly hamper muscle synthesis and thus also result in less energy being spent on these processes.

Additionally, when placed in a state of starvation, our bodies adjust to the changing conditions by lowering our energy expenditure in an effort to conserve energy (Kosmiski et al. 2013).

Because of this inability to accurately predict the “calories out” side, simply adjusting your caloric intake without considering the composition of foods you eat until your weight start to rise or drop might simply lead to you fattening or starving yourself.

Veldhorst, M. A., Westerterp-Plantenga, M. S., & Westerterp, K. R. (2009). Gluconeogenesis and energy expenditure after a high-protein, carbohydrate-free diet. The American journal of clinical nutrition, 90(3), 519–526. 10.3945/ajcn.2009.27834.

Kosmiski, L., Schmiege, S. J., Mascolo, M., Gaudiani, J., & Mehler, P. S. (2014). Chronic starvation secondary to anorexia nervosa is associated with an adaptive suppression of resting energy expenditure. The Journal of clinical endocrinology and metabolism, 99(3), 908–914. 10.1210/jc.2013-1694.