All Calories are NOT Created Equal

I hate to admit it, but it makes me happy that I hear fewer people talking about calories. (I hate to admit it because it means I’m a nutrition nerd! Ha!) However, there are still way too many people who think “a calorie is a calorie” and that weight maintenance happens when calories in equal calories out.

So, let me be very clear about this… all calories are not created equal.

Or said another (and slightly more accurate) way, the source of your calories matters as does how your unique body responds to and handles them.

What is a calorie?

Let me get all science-y for a minute and explain how we ever reached the idea that nutrition was all about calories…

A calorie is a unit of energy, just as a Joule is a unit of energy. One calorie (or 4.184 Joules) is the amount of energy required to raise one gram of water by one degree Celsius. Technically, calories can be measured in anything that gives off energy when burned like gasoline or food.

(Note: the calories in food are technically kilocalories or Calories. In other words, a food that has 200 “calories” will raise the temperature of 200 kilograms of water by one degree Celsius. But since no one thinks of it this way and none of us care about raising the temperature of water with the food we eat, I will refer to the energy produced by food as calories and not kilocalories for ease of understanding.)

What about calories in food?

When we talk about the calories in food, we are talking about how much energy that food will give us when it is burned during metabolism (a fancy word that means our body takes something and chemically transforms it into something else). The calories in food were originally measured by burning the food in a bomb calorimeter, which is a sealed container surrounded by water. Literally, the food would be torched until all that was left was ash and the temperature increase of the surrounding water was measured to determine how much energy was given off by the burning food.

So, in theory, the calorie in vs calorie out theory should work. You eat food to get energy and you burn energy through living, breathing, moving, etc. If you eat more energy (whether from carbohydrates, protein or fat) than you burn, it gets stored as fat. And if you burn more energy than you eat, then you will use your stored energy (i.e., fat) to make up the difference.

Why does “calories in vs calories out” not work?

The breakdown happens because we are not bomb calorimeters and it is virtually impossible for us to accurately measure our calories in and our calories out! Our bodies are not a simple sealed container surrounded by water with a Bunsen burner underneath. Everything about our metabolic process and the complexity of the food we eat impacts how our bodies respond. Not to mention that how your body works and the environment in which you live is unique to you and makes a difference in the totality of your bodily processes, including your metabolism.

Here are just a few things to consider about why measuring calories in and out is impossible:

  • Your body uses more energy to breakdown and use complex foods than it does to breakdown simple foods. (This use of energy is known as the thermic effect of food [TEF], and interestingly foods with a higher TEF have been shown to be more satiating.)
  • Your body cannot breakdown all foods the way a fire can burn them up. Remember: no human has the ability to digest fiber; so even though there are calories in fiber, we don’t have access to them. In addition, some people do not have the necessary stomach acid, digestive enzymes or bile to fully digest different macronutrients.  If they are not digested, they are not available for absorption and, if they aren’t absorbed, they can’t be turned into energy.
  • The chemical reactions in your body that turn food into calories need various micronutrients in order to occur. (For example, you need thiamin in order to metabolize carbohydrates and amino acids.) If you are not getting enough of the required vitamins and minerals, then the process literally cannot occur and your body must divert that food to a process other than the one that turns it into energy.
  • Your body may or may not know what to do with any food-like products that you eat.
  • Your body may have to store fat-soluble toxins of which it can’t dispose, which means it must wrap them in fat (i.e., potential energy) rather than use it.
  • How much energy you burn is difficult to measure because of factors like…
    • Fidgeting,
    • Temperature regulation,
    • Rate of breathing (not always related to exercise),
    • Amount of muscle and lean body mass, and
    • Amount of brown vs white fat cells (brown fat cells burn energy and give off heat while white fat cells just store energy).
  • Your hormonal regulation impacts whether you burn or store energy. Many people know that low thyroid function leads to weight, but other hormones like growth hormone and testosterone are involved as well. Your sleep pattern also makes a difference to whether your hormones are in balance and benefit your waistline.
  • Your microbiome helps determine how many calories from the food you eat are available to you and what your body does with them. (Different types of gut bacteria literally release more calories from food and send signals to your body that say you should burn the energy provided or store it for later use.)

So what should we do?

Because it is so difficult to get an accurate measure of calories in or calories out, I rarely recommend that anyone count calories. Rather, I suggest focusing on the types of food you eat (more real food and veggies anyone?!), getting regular exercise (although you can’t exercise your way out of the wrong diet) and putting your effort into keeping your bodily systems in balance, including your hormones and microbiome.


— Armougom F, Henry M, Vialettes B, Raccah D, Raoult D. Monitoring bacterial community of human gut microbiota reveals an increase in Lactobacillus in obese patients and Methanogens in anorexic patients. PloS one. 2009:4(9); e7125.
— Crovetti R, Porrini M, Santangelo A, Testolin G. The influence of thermic effect of food on satiety. European journal of clinical nutrition. 1998:52(7);482-488.
— Hampton T. “Browning” of White Fat May Help in the Ongoing Fight Against Obesity. JAMA. 2012;308(11):1080.
— Scientific American. How do food manufacturers calculate the calorie count of packaged foods? Accessed on April 9, 2015.
— Van Cauter E, Knutson K, Leproult R, Spiegel K. The impact of sleep deprivation on hormones and metabolism. Medscape Neurology. 2005;7(1).

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