Nutrition Overview - What's a Calorie?
TL; DR:
1) All food sources undergo a series of acidic or enzymatic breakdown before being absorbed into the body.
2) Calories are a way of assigning a reference point of energy found in food products.
3) One Calorie is the amount of energy required to raise one kilogram of water by one-degree Celsius.
4) The major macronutrients are Carbohydrates, Protein, Fat, and Alcohol.
a. Carbohydrates contribute 4 Calories per gram.
b. Protein contributes 4 Calories per gram.
c. Fat contributes 9 Calories per gram.
d. Alcohol contributes 7 Calories per gram.
Previous blogs have introduced the topic of energy systems, which is an excellent segue into discussing nutrition, particularly macronutrients and calories.
As an overview, we can revisit some of the information from the oxidative system blog.
When we eat our food, initial processes of breakdown and absorption occur throughout the digestive canal. Whatever was ingested will be pre-digested by acids and enzymes found within this canal at various sites (for example stomach acid, or amylase found in our saliva), the purpose of which is to have the final absorbed product be as close to its smallest functional component as possible. Once this is accomplished, all absorbed material can be delivered to their site of storage (for example, muscle glycogen or adipose fat) or immediate use.
The primary macronutrients utilized by our body are protein, carbohydrates, fat, and to a lesser extent, alcohol. Each of these macronutrients is capable of being broken down for the purposes of energy production. They are assigned a Calorie value per gram of macronutrient – carbohydrates and protein contribute 4 Calories per gram, fat 9 Calories per gram, and alcohol 7 Calories per gram.
Briefly, Calories (or kilocalories / kcals) are simply a unit of measurement to help organize and quantify the stored energy found within the chemical bonds of each macronutrient. One Calorie is the amount of energy required to raise one kilogram of water by 1-degree Celsius. As explained during the oxidative system blog, when we strip-mine each of these macronutrients through energy system processes,
it is the energy found in their bonds that ultimately contributes to the reproduction of our body’s ATP. When Calorie values are being determined, these Calories are assigned based upon the amount of energy given off via combustion (see: blowing them up), and determining how much energy was produced relative to the aforementioned amount of energy required to raise one kilogram of water by 1-degree Celsius. With this in mind, the concept of “energy dense” food begins to have a lot more context.
In order to be harnessed for energy, a series of chemical reactions will breakdown our food storage molecules (glucose or fat). Protein (in the form of amino acids) would require preparatory transformative reactions before entering those energy producing cycles. Regardless of food source, once these storage molecules are broken down into the appropriate precursory substrates (glucose, fatty acids, etc.), they enter the energy production cycle most appropriate for the level of energy demand of the body. If exercise is occurring, it will likely be a combination of the phosphagen, glycolytic, and oxidative systems at work. If at rest, the oxidative system will be predominantly active as there is adequate time for long-form energy production to meet the demand of the body.
Dietary nutrition can be broken down into two major categories for consideration, being, individual daily Calorie needs in addition to individual daily nutrient needs. For the purposes of these blogs, nutrients can be thought of as are our vitamins, minerals, baseline required macronutrients, fibre, and water. Each of which will be discussed moving forward.
Best,
Eric