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Home » News » Better Understanding "Calories In, Calories Out" for Weight Loss (or Gain)

Better Understanding “Calories In, Calories Out” for Weight Loss (or Gain)

Dr. Layne Norton spills the truth about CICO

Written by Stephen Sheehan, ISSA CPT, CNC, CSCS
Last updated on April 30th, 2025

Despite what some people want you to believe, calories do matter.

While certain factions of the health and fitness community seem committed to ignoring the golden rule of calories in, calories out (CICO), Dr. Layne Norton certainly isn’t one of them. On the contrary, the well-known strength coach and nutrition expert pounded the table for this time-tested principle while poking more than a few holes in dubious claims made by a fellow industry “expert.”

In a YouTube video published on Nov. 15, 2024, Norton provided a brief but poignant lesson that confirms CICO still holds weight no matter which direction you’re trying to move the needle on the scale.

https://www.youtube.com/watch?v=TsG6EHiVYEI

[Related: Best Supplements for Weight Loss]

Misconceptions About Calories In, Calories Out

Like Norton, Dr. Mark Sisson has carved out a lucrative niche as a leading voice in the nutrition space. However, the founder of Primal Kitchen Foods — a company that makes condiments and other food products with no added sugar or dairy — doesn’t share the same sentiment about CICO as someone with a PhD in nutritional sciences.

Norton picked apart pieces of a recent conversation Sisson had on a subject that still seems to be misunderstood despite plenty of evidence supporting its efficacy. To clear up any confusion about what CICO actually means (and to counter Sisson’s claim that it’s more “nuanced” and “complicated” than that), Norton provided the following definition:

“Calories in is the amount of metabolizable energy that goes into your system. Calories out is the total amount of calories, or energy, that you expend on a daily basis.”

Seems straightforward, right?

View this post on Instagram

A post shared by Layne Norton, PhD (@biolayne)

[Related: Best Fat Burners]

Yet Sisson still tried to find another reason not to toe the energy balance line.

“Take in calories and you don’t store them, maybe it’s because you burn them off thermogenically,” he proposed. “Maybe it’s because you literally crap them out because you have bad digestion.”

Needless to say, Norton wasn’t going to let either of those counterarguments carry any weight.

  • Thermogenesis — the process of heat production that occurs in all warm-blooded animals — plays a direct role in the “calories out” part of CICO.
  • According to Norton, research shows that the variance in metabolizable energy between individuals is less than 5-10%.

“Mark may have a misunderstanding of what calories in, calories out is because so far he’s actually describing it,” Norton remarked.

Debunking the Protein Myth

Sisson dug himself into an even deeper hole by trying to portray protein in an accurate light, claiming that the most important macronutrient is not “combustible.” Norton countered with a list of biological processes that allow the body to break down protein while also addressing how the thermic effect of food (TEF) factors in.

“Protein has a higher TEF than carbohydrate or fat, but that is also accounted for in calories out,” Norton explained. “Him saying protein is not combustible is false, demonstrably false.”

View this post on Instagram

A post shared by Layne Norton, PhD (@biolayne)

Here are other relevant points raised during the diet-centric discussion:

  • Less than 2% of the fat you store in adipose tissue originates as carbohydrate.
  • Over 98% of the fat that you store in body fat originates as dietary fat.
  • If you eat a high-carb, low-fat diet, your fat burning drops, but you’re also not storing much fat.
  • If you eat a high-fat, low-carb diet, you’ll burn and store a lot of fat due to the absence of carbs.

Listen to Layne: Whether or not you gain or lose body fat will depend on whether or not you’re consuming more overall calories than you burn.

Ultimately, no matter what Sisson (or other CICO cynics) try to say about TEF, the combustibility of protein, or other factors, losing or gaining weight boils down to a simple formula: Calories In vs. Calories Out.

So, as much as some people want to find a reason to not subscribe to this research-backed theory, the answer is right in front of you.

More Latest Research

  • How Much Protein Can Your Kidneys Really Handle?
  • Energy Compensation Might Be Affecting Your Weight Loss — Here’s What You Need to Know
  • Your Belly Fat Might be Healthier if You Work Out, New Research Suggests

Featured Image: New Africa / Shutterstock

About Stephen Sheehan, ISSA CPT, CNC, CSCS

Stephen is an ISSA-certified personal trainer and nutrition coach as well as a Certified Strength and Conditioning Specialist. A two-time University of Florida graduate and longtime rugby player, he brings over ten years of strength training experience to BarBend, with particular expertise in personal training, nutrition, weight loss, and sport-specific strength and conditioning tactics. When he’s not writing or hitting the gym, he enjoys traveling, cooking, and practicing his DJ skills.

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