3 Reasons a Calorie Deficit Didn’t Work for You

I’m going to be frank with you:

If a calorie deficit “didn’t work” for you, then you weren’t ACTUALLY in a calorie deficit.

The human body is complex, but not complex enough to deny the laws of physics.

  • The 2nd law of thermodynamics is a fundamental concept in weight management. It states that we cannot create nor destroy energy. To state that a calorie deficit “didn’t work” for you would b to claim that you created energy out of thin air.

Clearly, though, if you attempted to lose weight and didn’t, something DID go wrong.

So, the aim of this article is to outline what could have possibly gone wrong so you can more effectively audit your process and make better progress going forward.

Quick definition

It’s worth simply reiterating what a calorie deficit is.

Your body burns a certain amount of energy (calories) to fuel its daily functions such as your heart beating, breathing, walking, or other exercise.

It takes in a certain amount of energy (calories) from food each day.

Calories are the unit of measurement for energy, the same way that an inch is a unit of measurement for distance.

If your body takes in less calories from food than it burns each day, then your body is in a calorie deficit.

This forces it to tap into stored energy, such as body fat, to fuel its essential functions.

This is known as the energy balance model of obesity, and it is quite widely accepted now as the driving model of weight management.

Many people attempt to enter a calorie deficit as described above and do not lose weight.

As I mentioned previously, if this has happened to you, the truth is you weren’t actually in a deficit of calories.

So, below is a list of what likely did go wrong:

You mis-tracked your calorie intake

Tracking calories is hard. eye-balling it is harder. Doing either of which when you’re new is even harder.

People very commonly make mistakes when attempting to track calories.

A study from Lichtman et al. looked at the difference between how many calories their subjects reported eating versus how many calories they actually ate.

The average subject reported an intake of 1053 calories per day but ACTUALLY ate 2081 calories per day.

In other words, they underreported their actual calorie intake by over 1000 calories.

What could possibly cause this? In my experience, here are some of the most common culprits:

  • Misunderstanding portion sizes

    • If you’ve never actually measured out a serving size of peanut butter, you’d be surprised.

    • An example of this would be pouring three servings of your coffee creamer thinking it’s one serving.

  • Not tracking the “sneaky calories”

    • Sometimes, people will track most things right but consistently leave out a few key foods.

    • An example of this would be condiments. If someone is liberal with their barbecue sauce, they can easily add 100-300 calories to a meal and not even realize it.

  • Not tracking the “snacks, bites, tastes, licks”

    • Say you take one bite of your child’s pop-tart before leaving for work in the morning. At work a coworker says you “have to try this coffee,” and you take a sip. Four more instances such as these occur throughout the day. Before you know it, you’ve added another 100-300 calories to your day.

You misunderstood your calorie output

“Calorie output” refers to how many calories your body burns in a single day.

The same study as previously mentioned also looked at their subjects’ reported calorie output versus their actual calorie output.

They found that the average subject over-reported calorie output by 51%!

Similarly, the “calories burned” section on your smartwatch has been shown to be up to 30-90% inaccurate. [source]

Lastly, many TDEE equations are only about 63% accurate. [source]

With all this working against you, it becomes incredibly difficult to actually know how many calories your body is burning each day.

It is very common for people to assume they are burning more calories in a day than the actually are.

The FDA lied to you

Okay, not really, but kind of…

The FDA allows for up to 20% of variance on the calories reported on a food label.

More specifically, they say that a food product must be at least 80% accurate.

Why would they do this?

Well, to get from 80% accuracy to 100% accuracy 100% of the time would require an immensely greater amount of work on the side of the food companies.

The price of food would increase substantially. That would be a problem, likely, of greater severity than the 20% of variance allowed.

Nonetheless, it’s one of those things that can make getting your own personal energy balance in order that much more difficult.


Overall, nailing a calorie deficit can be tough and tracking calories can be frustrating.

I often recommend people focus on the behaviors that lead to less calories first, then worrying about tracking.

If that strategy would interest you, I’ve written an article outlining the 8 best habits to accomplish this.

You can find it here.

If you have any questions left unanswered, please feel free to comment below.

Zachary Keith, BSc CSCS CISSN

I’m a sports nutritionist, strength & conditioning specialist, remote coach, and owner of Fitness Simplified. I help people develop all aspects of their fitness as time-efficiently as possible.

If you’re interested in feeling your best & being your highest-performing self without fitness consuming your life, then my content and services are for you.

For my best free content, click here to subscribe to my weekly newsletter: Fitness Simplified Fridays!

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