Dietary Protein

Essential vs. Nonessential Amino Acids

Amino acids are the building block of proteins, as proteins are made up of many amino acids that are linked together by peptide bonds. The peptide bonds of proteins give the protein its shape and structure. The shape and structure of the protein affect the function of the protein. There are 9 essential amino acids and 11 nonessential amino acids.

Essential amino acids gained their name because they cannot be produced by the body and have to be consumed within the diet.

Nonessential amino acids are produced by the body through a process called transamination.

This simply means that an essential amino acid can be made into a nonessential amino acid or nonessential amino acids can be made into another nonessential amino acid depending on what the body is in need of. The body is constantly breaking down proteins and making proteins to aid in many different physiological processes, this is called protein turnover. The body uses an estimated 300g of protein every day for protein synthesis or the building of protein in the body; 200g comes from amino acids that result in the breakdown of bodily protein, the other 100g comes from dietary protein.

• Essential Amino Acids

  1. Histidine

  2. Isoleucine

  3. Leucine

  4. Lysine

  5. Methionine

  6. Phenylalanine

  7. Threonine

  8. Tryptophan

  9. Valine

• Nonessential Amino Acids

  1. Alanine

  2. Arginine

  3. Asparagine

  4. Aspartic Acid

  5. Cysteine

  6. Glutamic Acid

  7. Glutamine

  8. Glycine

  9. Proline

  10. Serine

  11. Tyrosine

Complete vs. Incomplete Proteins

Complete proteins are food sources that contains the necessary amounts of all 9 essential amino acids to support protein synthesis in the body.

Incomplete proteins are sources of protein that are missing some the essential amino acids needed for proper protein synthesis in the body.

• Complete Protein Sources

  • Meat

  • Poultry

  • Fish

  • Eggs

  • Dairy products

  • Quinoa

• Incomplete Protein Sources

  • Nuts

  • Seeds

  • Beans

  • Legumes

  • Tofu

Combining both complete and incomplete protein sources to have all 9 essential amino acids within your meal is a common practice, especially for those who eat a plant-based diet. A few examples of these combinations are eating rice with beans or having peanut butter sandwich.

Effects of Insufficient Amino Acid Intake on Health and Disease

Adequate protein intake is crucial to maintain health and prevent disease. Protein is needed for growth and development at every life stage. Remember protein is broken down each day due to protein turnover! We have to replenish our protein so the bodily processes that rely on it function properly. If the body is not consuming all of the essential amino acids, specific proteins may be disrupted. Proteins work to transport other amino acids to other cells and parts of the body. The protein collagen protects our skin, joints, and ligaments. Certain proteins help to regulate and maintain fluid balance within the body. The hormones insulin and glucagon are protein hormones and they work to regulate blood sugar levels in the body. Antibodies that help us fight illness are made from proteins and they strengthen our immune systems. These are just a few of the important functions proteins serve within the body. When we lack a sufficient amount of protein in the diet we may get sick more often, have brittle hair and nails, weak muscles, lack energy and feel more hungry.

 Effects of Excess Protein Intake on Health and Disease

Excess protein may have negative effects on kidney and bone health in the long term but there are proactive ways to counterbalance a diet that is high in protein. The breakdown of protein results in a toxic product called urea. Urea is excreted by the kidneys through urination and increases water loss. Some studies have shown that excess protein intake leads to an increase of calcium excreted in the urine, which can affect bone strength long term. Making sure you are meeting an adequate intake of calcium along with a high protein diet can increase bone mass and results in fewer fractures so the data is skewed on this outlook. If we are excreting more calcium through urination this can affect our kidneys by calcium deposits building up, causing kidney stones. This can be counterbalanced with a higher intake of water. Heart disease and cancer risks are increased with high protein diets, depending on the type of protein consumed. Eating mostly red-meat and other animal based protein products, like dairy, results in a diet high in saturated fat. Consuming a high intake of saturated fat increases the risk of developing cardiovascular disease and cancer. When determining how much protein to consume in your diet the recommended daily allowance (RDA) is 0.8g/day per kilogram of body weight. Another easy way to determine is to have 10%-35% of your daily calories come from protein. Again, making sure to eat complete proteins or combining both incomplete and complete proteins to meet all essential amino acid needs is crucial to maintain health of bodily functions that rely on protein.

References :

 1.  Smolin, L. & Grosvenor, M. Nutrition: Science and Applications. 4th ed. Wiley; 2019.