What is a calorie anyway?

Disclaimer: We need to note that this is not a discussion about whether the quantity of food is relevant to weight loss but rather if the current way we measure the quantity is an accurate means of determining how much energy is in the food we eat.

The world of nutrition resembles a street fight more than science. Battle lines are drawn and then each side attacks the other. Everyone thinks the other side is filled with dangerous idiots.  Nowhere is the battle more intense than over calories. Now there are different shades to each side but to boil it down to black and white there are essentially two groups.  The calorists are people who think that when it comes to weight loss that calories are calories regardless of where they come from. On the other side stand those who think calories don’t matter or at least the source of the calories changes the equation

While there is little apparent common ground between the sides there is one thing most people in the argument seem to share. Almost no one really seems to understand or if they do grasp the importance of what a calorie is. It is crucial for weight loss that we understand the word calorie.

What is a calorie?  

As all my calorie in/out friends will tell you it’s a unit of measure of energy. When someone declares that not all calories are created equal the response is usually that calories are simply a unit of measure like a mile or a kilogram so it’s illogical to say one calorie is different from another. If it is simply a unit, like a mile or meter, how can they be different?

On the surface this makes sense. Miles are miles, meters are meters, degrees are degrees.  If we dig a little deeper though there is a problem with this logic.  A couple of summers ago some friends and I were on the coast of Vancouver Island in Canada and booked a hotel that was just 5 miles from where we wanted to be. The problem was that where we wanted to be was on the other side of a body of water with no bridge across. We would have to drive inland a good distance and then back to the water. The hotel was by one measure 5 miles from our destination by boat but by car it was over 45 miles. Thankfully is was Canada and they apologized and refunded our money, but the lesson is still that context matters when we measure. How and what we are measuring is important.

The same is true of energy. A calorie of food is potential energy. If the way we measured that potential energy and the way we are using it are different it is likely that the we cannot use all of the potential energy. Depending on the differences we may not be able to use it all.  Coal has a lot of potential energy but would be of little use for your car.  Calories then would need to be measured in a way that is equivalent to how a body uses them for calories to be calories.  

How do we measure calories?

There are two main units we use when talking energy. The kilojoule which is work and force based and calories which is heat based. In terms of food we are usually talking kilocalories or Kcal, which is defined as amount of energy to raise a kilogram of water by one degree Celsius. One kilocalorie is equal to just over 4 kilojoules. The question is why in the world would we use a measure of heat and not work to determine how much energy we derive from food?  

Let me introduce you to the bomb calorimeter. This device we use to measure the caloric content of our food, is essentially a sealed box filled with oxygen and food. That box is inside another container that is filled with cold water. An electric spark ignites the food and the food is burned. The resulting temperature rise in the surrounding water is then measured with every degree in temperature increase corresponding to a calorie.

One more time in case you missed it, we measure the amount of energy in our food by literally burning it. This should seem ludicrous because it is. You don’t need a PhD in physiology to know your body doesn’t actually burn our food to create energy. It’s a far more complex process than that involving the krebs cycle, glycolysis and a whole host of other functions including digestion. Just because burning one gram of fat results in a nine degree increase in the water temp while carbohydrates increase the temp by only four doesn’t mean that ratio holds true in the body.

This is fact. Resistant starch is so named because it is resistant to digestion meaning what we measured via burning doesn’t equate to actual energy. While this example is obvious because only part of the food is digested all food has similar issues when trying to correlate energy from a bomb calorimeter into the body. We need to digest and convert all of the food to ATP. This process costs energy and is inefficient. Even if there are no effects on metabolism based on food consumed there is a high degree of variability on these factors.

Still not convinced. Remember literally anything that has energy can be measured the same way. A gallon of gas has almost 30,000 calories while a kilogram of coal has about 6,500 kcal per kilogram.  Does anyone think drinking gas or eating coal, even if they weren’t toxic, would be useful energy in the body?

The fact that most nutrition experts don’t understand this problem should tell you how far we are from understanding the nutrition problem. This though is not the only problem that our current system of measurement poses. More to come in part 2.