Is Weight Loss As Simple As Calories IN vs Calories OUT?

It is true that getting the balance of CALORIES IN vs CALORIES OUT (CICO) should be the priority for weight loss and to some degree the "eat less, move more" advice from some PT's and nutrition coaches is correct, however in my view this is far too simplified and often frustrating advice for clients to work with as there are many other factors you need to consider when striving to lose weight...


CICO goes beyond food and exercise.

“Eat less, move more” only takes into account the calories you eat and the calories you burn through exercise and other daily movement. But CICO is really an informal way of expressing the Energy Balance Equation, which is far more involved.

The Energy Balance Equation—and therefore CICO—includes all the complex inner workings of the body, as well as the external factors that ultimately impact “calories in” and “calories out.”

Imperative to this, and often overlooked, is your brain. It’s constantly monitoring and controlling CICO. Think of it as mission control, sending and receiving messages that involve your gut, hormones, organs, muscles, bones, fat cells, external stimuli (and more), to help balance “energy in” and “energy out.”

It’s one hell of a complicated—and beautiful—system.

Yet the Energy Balance Equation itself looks really simple. Here it is:

  • [Energy in] – [Energy out] = Changes in body stores*

*Body stores refers to all the tissues available for breakdown, such as fat, muscle, organ, and bone. I purposely haven’t used “change in body weight” here because I want to exclude water weight, which can change body weight independent of energy balance. In other words, water is a confusing, confounding variable that tricks people into thinking energy balance is broken when it’s not.

With this equation, “energy in” and “energy out” aren’t just calories from food and exercise. As you can see in the illustration below, all kinds of factors influence these two variables.

When you view CICO through this lens—by zooming out for a wider perspective—you can see boiling it down to “eat less, move more” is a significant oversimplification.

Calorie calculators and CICO aren’t the same.

Many people use calorie calculators (eg: MyFitnessPal / FitBit / Apple Watch) to estimate their energy needs, and to approximate how many calories they’ve eaten. But sometimes these tools don’t seem to work. As a result, these individuals start to question whether CICO is broken. (Or whether they’re broken).

The key words here are “estimate” and “approximate.”

That’s because calorie calculators aren’t necessarily accurate.

For starters, they provide an output based on averages, and can be off by as much as 20-30 percent in normal, young, healthy people. They may vary even more in older, clinical, or obese populations.

And that’s just on the “energy out” side.

The number of calories you eat—or your “energy in”—is also just an estimate.

For example, the FDA allows inaccuracies of up to 20% on label calorie counts, and research shows restaurant nutrition information can be off by 100-300 calories per food item.

What’s more, even if you were able to accurately weigh and measure every morsel you eat, you still wouldn’t have an exact “calories in” number. That’s because there are other confounding factors, such as:

  • We don’t absorb all of the calories we consume. And absorption rates vary across food types. (Example: We absorb more calories than estimated from fiber-rich foods, and less calories than estimated from nuts and seeds.)

  • We all absorb calories uniquely based on our individual gut bacteria.

  • Cooking, blending, or chopping food generally makes more calories available for absorption than may appear on a nutrition label.

Of course, this doesn’t mean CICO doesn’t work. It only means the tools we have to estimate “calories in” and “calories out” are limited.

To be crystal clear: Calorie calculators can still be very helpful for some people. But it’s important to be aware of their limitations. If you’re going to use one, do so as a rough starting point, not a definitive “answer.”