We have all heard the term Calories/kcal used in reference to food and seen the number on nutrition labels. How many know what it is? Would you be surprised to know that it is a unit for heat measurement?

A Calorie or kcal is the amount of energy required to raise the temperature of 1 kilogram of water by 1 degree. The reason it is defined as a heat measurement is due to how scientists determine how much energy a particular food has. This is done by placing the food in a bomb calorimeter and burning it. This causes the food to heat up the air that then travels into a copper tubing . From the copper tubing the heated air is used to heat up water outside of the device. The temperature of the water is then used to calculate the Calorie amount in the food. From here the scientists are able to determine the macronutrient (Protein, carb, fat) makeup of the food

This is not an exact science and there are 3 things that can affect the calculation.

1. The amount of heat released by the macro nutrient during combustion: The heat that is released due to combustion is a measure of the POTENTIAL energy stored within the macro’s molecular structure. However the laboratory environment is unable to properly simulate the human body with all the different variables each persons unique metabolism will exhibit. (Metabolism)

2. The percentage of the macro’s digestibility: The rate and % of the macro that is absorbed within the human body.  There are many factors that can affect our absorption/digestion of food. This changes the amount of food we can utilize and is different person to person.

3. The amount of nitrogen we lost through excretion: We lose some of the nitrogen stored in protein through the bodies digestion process. This becomes unavailable and therefore changes the net value of how much protein we are able to utilize. Just because the label says 25 g of chicken does not mean you are using all of it. This will also be a factor into why I might need to increase the amount of protein a client consumes. We are able to use about 91% of the protein we ingest for the creation of ATP.  When compared to a typical car (12-20% efficiency) the human body is very efficient. 

Looking at these 3 factors you can see why trying to be 100% accurate with your numbers is not going to happen.

This process is not without flaws. There are numerous factors that can impact the nutritional value of a food after the sample is taken.

• Starch and Fiber resistance: The Body does not get as much energy from these sources as compared to when it is combusted. This can lead to the carbs on the labels being inflated.
• Soil and Growing process: If the food was grown in nutrient depleted soil will make a difference. This will cause the numbers to be off as compared to the sample.
• Ripeness of the food: Food picked during peak season as compared to those picked out of season have different nutritional values.
• Animal Diet: For such foods as milk, eggs, meat,and fish what the animal eats will very the nutritional value of the food.
• Length of Storage: Eating food that was picked fresh that morning vs something that was picked a week ago will change the value of the food. Even more so for foods that have been shipped and transported only to be available for purchase 3 weeks from being harvested.
• Preparation and cooking method: The nutritional value of food changes once it has been cooked. In most cases cooking can make more nutrient available to us.

We can see why the nutritional labels on food are not 100% accurate. They are a mere estimation of what the food contains. There is no feasible way for a new sample of every product to be taken out of the ground, removed from the assembly line nor removed from an animal to be combusted to ensure accuracy whenever there is a change in the process or diet of the animal. Therefore scientists take a sample and use this as a standard for the product.

When you apply all of the above you can get a variation of +/- 25% difference. Digestion and absorption will add another 2-5%. I’m going to speculate that most people reading this are doing some form of exercise to benefit their health and help control their body composition. This will add an additional level of energy expenditure that is even more difficult to calculate.

As you can see calorie/macro counting is not an exact science. Trying to calculate every little macro on your meal plan to make 100% accurate exchanges in your meal plan will not only be inaccurate but cause more stress when the results do not match the numbers.

The best way to combat this seemingly overwhelming inaccuracy is to be as consistent as possible to your suggested meal plan. Once you have found what works, typically 3 weeks, then you are able to make SMALL controlled exchanges. Wait to see how your body responds so you understand if and how the new food works for your metabolism. Changing brands or foods just because they look the same adds unknown variables (Absorption, micronutrients,  label accuracy….) that take longer to adjust for. When I am making tweaks this is one of the big reasons, there are others, as to why I change the initial food amounts.