The CICO diet is a weight management approach based on the acronym “Calories In, Calories Out.” It operates on the fundamental premise that the quantity of energy consumed versus the amount of energy expended determines weight change. This concept is a straightforward model for achieving weight loss by intentionally creating a calorie deficit. It is a framework for energy balance that underpins all successful weight loss strategies, not a prescriptive diet with specific food rules.
The Fundamental Principle of Energy Balance
The CICO principle is grounded in the First Law of Thermodynamics, stating that energy cannot be created or destroyed, only transferred or transformed. Applied to the human body, the energy consumed must be accounted for by the energy the body uses or stores. Calories are the unit of energy measurement for the fuel we take in.
Weight remains stable when energy consumed matches energy expended, a state known as caloric maintenance. To achieve weight loss, the body must enter a caloric deficit, forcing it to draw upon stored energy reserves, primarily body fat, for fuel. Conversely, a caloric surplus results in the storage of excess energy, typically leading to weight gain.
Implementing the CICO Equation
Applying the CICO equation requires determining both sides of the balance. The “Calories Out” side is the Total Daily Energy Expenditure (TDEE), which represents the total number of calories your body burns daily. TDEE is composed of three main factors: your Basal Metabolic Rate (BMR), the Thermic Effect of Food (TEF), and activity expenditure.
Online calculators provide a starting estimate of your TDEE based on factors like age, sex, weight, height, and activity level. To lose weight, a sustainable approach is to subtract 500 to 750 calories from this TDEE estimate to create a daily deficit.
The “Calories In” side involves tracking every calorie consumed from food and drink, which requires meticulous logging and portion measurement. Using food scales, measuring cups, and tracking applications helps ensure consistency and minimize estimation errors in the recorded intake.
CICO and the Quality of Calories
While CICO is mathematically sound for weight change, it focuses only on energy quantity, not nutritional quality. The body’s response to 500 calories of highly processed sugar is not the same as its response to 500 calories of lean protein and vegetables.
Foods rich in micronutrients, fiber, and protein have a greater impact on satiety, or the feeling of fullness. Protein and fiber require more energy for digestion, slightly increasing the Thermic Effect of Food (TEF). They also help regulate hunger hormones, making adherence to a calorie deficit easier.
A diet solely focused on meeting a calorie target with low-quality foods can lead to nutrient deficiencies and persistent hunger. Therefore, CICO is most effective when used as a framework for energy control while prioritizing nutrient-dense foods for overall health and hunger management.