Calories In, Calories Out: A Brief Explanation of the First Law of Thermodynamics - My Mind My Body
Calories In, Calories Out: A Brief Explanation of the First Law of Thermodynamics

Calories In, Calories Out: A Brief Explanation of the First Law of Thermodynamics

This is a guest blog post from Rhiannon, one of my Intuitive Eating For Beginners group moderators on Facebook. She has so much experience with intuitive eating that I want to share some of her wisdom.

When I think about reverting back to dieting and counting calories, it helps me to know that the “calories in, calories out” meme is a HUGE misinterpretation of the first law of thermodynamics.

The first Law of Thermodynamics, or energy balance, basically states that in a closed system, energy can neither be created nor destroyed, only transformed or transferred.

Did you catch it? “In a closed system.” A campfire is a closed system. Nothing can pass through the system without being changed, chemically, into something else.

The human body, on the other hand, is an open system. Among other differences, this means that some substances can pass through our bodies without being altered at all. Drink a lot of water right before a urine test and the doctor will complain that there’s no urine to test; it’ll just be water.

Balance in an open system, like the human body, is when all energy going into the system equals all energy leaving the system PLUS the storage of energy within the system. It’s amazing how many calorie-counting diets manage to leave that last part out.

In real life, balancing energy includes a lot more than just the calories we eat and the calories we burn according to those exercise charts. The energy parts of the equation include:

  • Calories consumed

  • Calories converted to energy and used in involuntary movement

  • Calories used for heat generation and in response to external environmental exposures and temperatures

  • Calories used with inflammatory and infectious processes (so that your body can try to protect itself from unhealthy bacteria and diseases)

  • Calories used in growth, tissue restoration and healing

  • Calories used in numerous metabolic processes (so that your heart can continue pumping, and your brain can continue to perform cognitive functions, and your lungs can continue taking in oxygen, and your hair can continue growing, and your blood can continue circulating nutrients and oxygen throughout your body, etc.)

  • Calories used in voluntary movement

  • Calories used in digestive processes

  • Calories not absorbed in the digestive tract and matter expelled

  • Calories stored as fat

  • Fat converted in the liver to glucose

and many, many more.

To add to that, to put it simply: each variable affects the others, varies with mass and age, involves complex hormonal and enzyme regulatory influences, and differs in efficiency.

The human body is not a machine. There are countless, wildly varying, variables (external and internal) involved, that affect the efficiencies of the system and for which we have no control over. Understanding this helps to explain why calories cannot be balanced like a chequebook, and why people never seem to gain or lose precisely as calculated.

Calories eaten and calories used in voluntary movement are two small parts of a larger equation and are meaningless by themselves, unless all of the other variables are controlled for…which they can never be as they aren’t under our control.

Once I realized this, I stopped counting calories. Doing so is just a futile exercise. It’s useless to obsess about thermodynamics and calories, when most of the equation is not under my (nor anyone’s) conscious control.

 

References:

https://www.physicsforums.com/threads/open-closed-and-isolated-systems.460485/

 

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