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Myth Bust: “Why Calories In, Calories Out” Doesn’t Work 

Studies vary on weight loss success, but everybody knows from personal experience and a lot of research that keeping the weight off is another story. Despite that, the adage of “calories in, calories out” is a foundation of the diet and fitness industries, even if it is becoming more antiquated with time. 

This rule of thumb expression is thrown around as a matter of fact. It sounds like common sense. It makes taking on a new diet and fitness schedule sound simple and doable. The gyms fill up, diet programs sell memberships and supplements, and of course we all know it will only last several weeks before things return to normal. 

Like most reductionist phrases, there is a degree to truth about calories in, calories out but there’s a little more to the process. No two bodies are the same, and there are thousands of individualized factors ranging from genetics, stress, food quality, medications, gut microbiome, thyroid, and a fluctuating individual metabolic rate. There is nothing simple about understanding weight loss, but if the diet industry admitted that it’s not simple there would be far fewer initial efforts, leading to disappointment. 

As a society, we’ve internalized the “calories in calories out” mentality to the degree that every time a weight loss goal isn’t achieved, we blame ourselves instead of misleading advice. Additionally there’s a lot of shame attached to weight gain and those that are overweight, because society assumes it’s a reflection of character or self-discipline. If calories in, calories out worked – we probably wouldn’t be facing shortages of the weight-loss drug Ozempic. 

Instead “calories in calories out” hooks the public on a marketable, actionable item and places blame so that everyone keeps trying the same steps that often don’t pan out despite best efforts. Calorie tracking apps like My Fitness Pal are impossible for most to use accurately because it’s impossible to really know what’s even in our food and measure every bite.  

What is a calorie? 

“The term calorie has been in use since the early 19th century, when it was used to define the amount of heat required to raise the temperature of a kilogram of water from 0 degrees to 1 degree Celsius.” 

Each macronutrient contains the following calories per gram:

  • Carbohydrate: 4 calories
  • Fat: 9 calories
  • Protein: 4 calories

Common sense tells us that 1 gram of a carb is different than a gram of protein, yet they are the same caloric count. Most diet plans put increasing emphasis on the different types of calories, sending users down a rabbit hole of comparing the difference between medium and short chain triglycerides and whether an isolate protein powder is superior to a standard whey one. 

The reason “calories in, calories out” feels accurate is because most people have lost some weight with simple calorie restriction and more exercise. Even if they put weight back on after the initial weight loss. Most people blame a personal lack of follow through or discipline, and think “I’ll try again next year”  without questioning why it wasn’t sustainable to keep “healthy habits”. 

What “calories in calories out” doesn’t account for is an initial weight drop, but the body will hit a plateau phase. Lower calories eventually creates a slower metabolism. In turn the body burns those limited calories slower. This is a survival mechanism that the body wants to maintain the equilibrium it’s been sustaining. Of course, this plateau can be pushed through but it’s at this point when weight loss goals get sabotaged. At this point most people think they have to indefinitely keep up the same diet/fitness routine that lost the initial weight, but this is when many start gaining weight back.