Macronutrients And Their Function In The Body


Amino acids join to form proteins. There are 20 amino acids, 9 of which are essential and must be obtained through the diet. Amino acids are used in metabolic pathways and optimal levels of protein mean that proper metabolism can take place. 

The most important role of protein is to build and repair tissue. Protein is an important component of every cell in the body. 

When protein is consumed, it is broken down into amino acids, and they are used as precursors to:

  • nucleic acids (DNA and RNA)

  • co-enzymes

  • hormones

  • blood cells

  • immune response

  • enzymes

  • skin

  • hair and nails

  • bones

  • muscles

  • cartilage

The optimal amount needed in the diet will depend on the person's age, lean body mass, and whether or not they are in a caloric deficit.


 Fat provides:

  • energy storage

  • energy reserve

  • energy source during aerobic exercise

  • cell to cell communication and signalling

  • hormone production

  • enzyme co-factors

  • cell membrane constituents

  • protection for vital organs and provides thermal insulation

  • a source of essential fatty acids

  • a carrier for the fat soluble vitamins A, D, E, and K

  • necessary for growth and development


​The optimal level of fat in the diet will ensure hormonal balance and metabolic homeostasis.


Atoms of carbon, hydrogen, and oxygen combine to form a basic carbohydrate molecule. Carbohydrates can be classified as monosaccharides, disaccharides, and polysaccharides. The monosaccharide (mono meaning one and saccharide meaning sugar) represents the basic units of carbohydrates. The three monosaccharides are galactose, fructose, and glucose. When you consume a carbohydrate, it is eventually broken down into its monosaccharide constituents.   

Energy Source: Carbohydrates are the preferred energy source of working muscles as they can be metabolized both aerobically and anaerobically. Carbohydrates are the primary energy source for the brain and the sole energy source for red bloods cells. The brain alone requires 100-120 grams per day of carbohydrates for optimal performance.

Protein-Sparing: If carbohydrates are absent, the bodies depleted glycogen stores are not being replenished, and the body must break down proteins from muscles or vital organs or use dietary protein to make its own glucose. When carbohydrates are present in the diet, metabolic homeostasis is maintained, and protein can be used for building, repairing, and maintaining body tissue. 

Ketosis Prevention: When glucose is not available, fat is broken down for fuel. In this process, fragments of fat are used to produce ketones which are an alternative fuel source. Life cannot be sustained long-term using ketones. Accumulation of ketones in the blood causes ketosis and upsets the chemical balance in the blood.

Gut Bacteria: Ingestion of complex carbohydrates such as fibre and resistant starches leads to growth of healthy gut bacteria.

The optimal level of carbohydrates in the diet will ensure proper nervous system function and maintain metabolic homeostasis.


Shils, Maurice Edward, and Moshe Shike, eds. Modern nutrition in health and disease. Lippincott Williams & Wilkins, 2006.

McArdle, William D., Frank I. Katch, and Victor L. Katch. Exercise physiology: nutrition, energy, and human performance. Lippincott Williams & Wilkins, 2010.

Houston, Michael E. Biochemistry primer for exercise science. Human kinetics, 1995.