Calories In vs Calories Out

Most people attribute weight loss and gain to specific nutritional choices. Where foods like lean meat and veggies lead to weight loss, options like cookies and ice cream lead to weight gain.

But how true is this? Well, there is a sliver of truth here, but not for the reasons people typically think of. The truth is, it all comes down to a physiological equation…


Calories In vs. Calories Out (CICO)


Calories in/calories out is simply a measure of the number of calories we consume each day compared to the number of calories we expend. The calories in part of the equation is straightforward: it includes the calories we get through food, beverages, and supplementation.


The calories out part is a bit more nuanced because several components make it up: BMR, TEF, NEAT, and EAT. Let’s take a look at each:

  • BMR (basal metabolic rate) encompasses all of the processes the body carries out each day. These are the calories we burn at rest and account for up to 70 percent of our daily caloric expenditure (1).
  • TEF (thermic effect of food) refers to the energetic cost of breaking down food and absorbing its nutrients. Protein has the highest thermic effect - between 15 and 30 percent. Carbs have a thermic effect of five to ten percent, and fats have a TE of only one to three percent (2). For instance, if you eat 1000 calories worth of carbs, your body would expend between 50 and 100 to break it down and absorb it.
  • NEAT (non-exercise activity thermogenesis) accounts for all of the calories we burn through movement (3). Walking, brushing our teeth, and every other movement you can think of. NEAT can account for a significant caloric burn each day if the person is quite active (4).
  • EAT (exercise activity thermogenesis) refers to the number of calories we burn through dedicated exercise time.


Together, our BMR, TEF, NEAT, and EAT produce TDEE (total daily energy expenditure), which is the number of calories we burn each day.


What Role Does CICO Play In Our Lives?


Calories in vs. calories out is simply an equation that determines how much energy we consume in relation to our expenditure. It dictates how our weight changes over time or if it stays where it is. 


If we consume more calories than we burn, we gain weight in the form of lean muscle and fat tissue. If we consume fewer calories than we expend, we lose muscle and fat. And, if we consume roughly the same number of calories as we burn, we get to maintain our current weight.


Depending on the magnitude of surplus or calorie deficit, our weight can change rapidly or relatively slowly. For instance, if you only eat slightly more than you expend, you will gain weight slowly. In contrast, if you put yourself on a restrictive diet and consume far fewer calories than you burn, you can lose weight rapidly, but that also leads to significant muscle loss (5).


While many people love to attach the equation to nutritional quackery and diets or deny its existence, it is there. Just like gravity, it exists, and it works whether we like it or not. We can try to ignore it, but CICO dictates how our weight changes and how that impacts our health in the long run.




Despite kJ being Australia's standard for measuring energy, many people still opt to measure using calories. Here's a quick rule for conversion.


1 Calorie is roughly 4.18 kJ and 1 kJ is roughly 0.24 Calories.