Carbohydrates aid in maintaining the nervous system, thereby decreasing irritability. They are also necessary in the function of the brain. Without them, we experience mental fatigue and a decrease in our state of alertness. As well, carbs are necessary in the complete breakdown of fats. Carbs should comprise approximately 55 per cent of your daily food intake.

Unlike the other macronutrients -- protein and fat -- their breakdown begins immediately in our mouths, when mixed with our saliva's enzymes. Complex carbs are absorbed more slowly than simple carbs (found in processed foods.) This is important in maintaining non-fluctuating blood sugar levels in our blood. When the body has enough energy, glucose converts into glycogen which can't be stored beyond one day. Thus, our supply needs to be constantly replenished. We turn to carbs for energy, preventing us from needing to use consumed protein as our energy source.

Fat is also a macronutrient. According to the World Health Organization, a person needs approximately 20 per cent of their overall daily calories to be the macronutrient fat. Fat is used in the formation of the tissue structure of our cells. It's necessary in the synthesis of various chemicals in our bodies and assists in the transport of vitamins A, D, E and K. It's also needed for building metabolic activity and the formation of estrogen. Fat aids in nerve impulses and nerve transmission and insulates nerve fibers. It protects our organs, offering padding or shock absorption. Advantageously, it takes longer to digest, so it gives us a feeling of fullness, while making food moist, easier to chew and finally digest.

Protein is the final macronutrient and should comprise approximately 25 per cent of your daily caloric food intake. Unlike carbs and fats, protein cannot be stored in the body if this daily requirement is exceeded. It is composed of "amino acids", which are linked in long chains and often referred to as "the building blocks". Basically, proteins are composed of 21 varying amino acids: our bodies produce 12 non-essential amino acids. The remaining nine essential amino acids must come from the food we consume. There are two types of dietary protein: high quality and low quality. High quality proteins contain all nine essential amino acids in the proper proportions. The absorption of high quality proteins is much more efficient than low quality ones.

In our bodies, protein is needed for the growth and tissue repair of our ligaments, tendons, muscles, skin, hair and nails. It's also necessary for the formation of antibodies needed by the immune system, enzymes used in digestion and metabolism, some hormones (i.e. insulin) and hemoglobin. As a last resort, protein may also be used to supply the body with energy when we don't consume enough fats and carbohydrates. This scenario can typically be found with starvation and low- carb, low- fat diets OR when energy output is intense (eg. in a marathon).

Protein takes approximately four hours to break down. This process commences in the acids of the stomach, as stomach enzymes change the consumed protein into small chains of amino acids called "peptides". This digested protein then moves to the small intestine, where the alkaline environment allows a new set of enzymes to further breakdown the peptide chains into even smaller ones. The amino acids are then absorbed into the bloodstream and then transported throughout the body to our organs. In turn, the liver is the major site for metabolizing protein, creating serum proteins from amino acids.

When discussing carbs, proteins and fats, we can see that each one has a specific need in our bodies. It's also important to be aware of the proportional percentages (55 per cent good carbs, 20 per cent good fats and 25 per cent high quality proteins) for daily food intake. Coupled with daily exercise and a decrease in stress level, good health can be the enjoyable, long-lasting outcome!

Katherine Preston is a registered personal trainer and aqua-fitness instructor as well as a nutrition and wellness specialist. Contact her vat absfit@cogeco.ca You can also visit http://home.cogeco.ca/~absfit.