Carbs, Fats, Proteins Explained Part 1: Background

I’ve gotten many questions in the ATD mailbag about protein, carbohydrates and fat. Many people seem to be confused about what these molecules actually are and what they do. This is not surprising, as there is so much differing information out there. Therefore, I’ve decided to write an explanation, detailing their uses in the body and common misconceptions, particularly as they relate to health and fitness.

Before we get to each individual molecule, it is helpful to get a little bit of background on all of them collectively. As a group, they are called the MACROnutrients. The prefix “macro”, in this case, denotes that they are needed in large quantities (as opposed to the MICROnutrients <vitamins and minerals> which are needed in much smaller quantities).

Macronutrients differ from micronutrients in mainly two aspects. First, as we just explored, they are needed by the body in much larger quantities. We measure carbohydrates, fats, and proteins in grams, while we measure vitamins and minerals in milligrams and even microgram (a milligram is 1/1000 of a gram). Secondly, the macronutrients provide energy to the body, while the micronutrients do not.

This brings us to another important explanation which must be made before continuing the discussion on macronutrients. Obtaining energy through digestion of foods is a rather complex process, but basically, bonds between atoms are broken, resulting in energy release. This energy is trapped by the body and used however it is needed. Normally, all of the energy from every single piece of food that is eaten is derived by the body. Only the indigestible parts of foods are excreted (i.e.…cellulose, which we lack the enzymes to digest).

After food is broken down, there are several ways in which the energy can be directed. Again, biochemically, this is extremely complex, but basically, energy can either be used right away or it can be stored for later use. Examples in which energy would be used right away would be for moving nutrients around the body, tissue repair, movement, and keeping body temperature within limits.

When the energy derived from food is not needed right away, it can be stored in one of two ways: glycogen and body fat. As explained in a previous ATD blog post, glycogen is a glucose polymer, which can be stored in muscle and hepatic (liver) tissue. Therefore, glycogen is a very limited energy storage option. The vast majority of our energy is stored as body fat. Body fat and dietary fat, the fat in our diets, are very similar compounds. However, this does not mean that fat is eaten, and stored without first being digested. As with all foods, if dietary fat is ingested, it is completely broken down, and then reassembled.

Hopefully, this has given you a better understanding of macronutrients as a group and why they are important. Next post, we will talk about how energy is measured and common misconceptions (Kcals vs. calories vs. kilocalories, etc…).