PROTEINS 1

PROTEINS 1

1. WHAT ARE PROTEINS

   • ORGANIC COMPOUND MADE UP OF CARBON, HYDROGEN, OXYGEN AND NITROGEN ATOMS
   • BODY'S ONLY SOURCE OF NITROGEN
   • MADE UP OF UNITS OF AMINO ACIDS, NUMBERING FROM 2 TO A FEW THOUSANDS

2. WHAT ARE AMINO ACIDS?

   • THE BUILDING BLOCKS OF PROTEINS
   • VARY BASED ON THE STRUCTURE OF THE SIDE GROUP
   • 2 AMINO ACIDS COMBINE TO FORM A DI-PEPTIDE, 3 AMINO ACIDS COMBINE TO FORM A TRI-PEPTIDE, MANY AMINO ACIDS COMBINE TO FORM A POLYPEPTIDE (PROTEIN)
   • CLASSIFICATION OF AMINO ACIDS
     • ESSENTIAL AA
       • AAs THAT OUR BODY CANNOT SYNTHESISE, MUST BE OBTAINED FROM FOOD
         • 9 ESSENTIAL AAs
           • METHIONINE
           • TRYPTOPHAN
           • VALINE
           • PHENYLALANINE
           • THREONINE
           • HISTIDINE
           • ISOLEUCINE
           • LEUCINE
           • LYSINE
     • NON-ESSENTIAL AA
       • AAs THAT OUR BODY CAN SYNTHESISE, NOT ESSENTIAL TO BE OBTAINED FROM FOOD
         • 11 NON ESSENTIAL AAs
           • ALANINE
           • GLUTAMINE
           • ASPARAGINE
           • SERINE
           • ARGININE
           • GLYCINE
           • ASPARTIC ACID
           • PROLINE
           • CYSTEINE
           • TYROSINE
           • GLUTAMIC ACID
     • CONDITIONALLY ESSENTIAL AAs
       • AAs THAT IS NORMALLY NON-ESSENTIAL, BUT UNDER SPECIAL CIRCUMSTANCES, MUST BE SUPPLIED BY THE DIET TO MEET BODY'S REQUIREMENTS
         • HAPPENS WHEN THE BODY'S NEED EXCEEDS THE BODY'S ABILITY TO PRODUCE IT
           • IF DIET FAILS TO SUPPLY AN ESSENTIAL AA
           • DUE TO INHERITED DISEASES, THE BODY IS UNABLE TO SYNTHESISE AN AA FROM A NON-ESSENTIAL AA
       • E.G. GLUTAMINE IN ADVANCED LIVER DISEASE
       • ARGININE DURING CONDITIONS OF ILLNESS/ TRAUMA
       • E.G. TYROSINE IN AN INHERITED DISEASE PHENYLKETONURIA (PKU)
         • PHENYLALANINE (EAA) CANNOT BE CONVERTED TO TYROSINE DUE TO ABSENCE OF PHENYLALANINE HYDROXYLASE
           • PEOPLE WITH PKU DO NOT HAVE PHENYLALANINE HYDROXYLASE, SO THEY CANNOT MAKE TYROSINE. SO TYROSINE NEEDS TO BE CONSUMED, MAKING IT A CONDITIONALLY ESSENTIAL ACID
           • PHENYLALANINE NOT CONVERTED TO TYROSINE, ACCUMULATES IN BLOOD, CAUSES IRREVERSIBLE BRAIN DAMAGE

3. PROTEIN STRUCTURE

   • Proteins differ based on the types of amino acids and chain length. The sequence of amino acids makes a big difference Even if one amino acid were different, the implications could be severe.
   • Hemoglobins are proteins in our red blood cells that carry oxygen. It is made up of 4 chains – 2 alpha chains (141 amino acids each) & 2 beta chains (146 amino acids each). (Total : 574 amino acids)
     • If only one of the beta chains is affected, the person is a carrier for sickle cell disease. The condition is called sickle cell trait. With a few rare exceptions, people with sickle cell trait are completely normal
       • Sickle cell disease is a genetic disorder – acquired from parents’ genes. Sickled cells – unable to carry oxygen effectively and hamper blood flow.

4. FUNCTIONS OF PROTEINS

   • 1. Vital Part of Body Structures
     • Every cell in the body is made of proteins. Muscles, blood cells, tissues, enzymes, immune bodies, lipoproteins, hair, finger, nails, skin, etc As protein forms the building blocks of most body structures, the need for proteins is high during periods of growth (children, teenagers) Proteins are also needed for replacement. The life span of our skin cells is about 30 days, cells of the intestines are replaced every 3 days.
   • 2. Regulate Body Processes
     • Digestive enzymes are proteins that digest (breakdown) carbohydrates, lipids and proteins into smaller structures for absorption by our intestinal cells
     • Hormones are the body’s internal chemical messengers. Adrenaline, the ‘emergency hormone’, is released when we are scared or excited. Responsible for our increased heart rate in such circumstances Insulin, is released by the pancreas when blood glucose levels are high. They cause our liver and muscles to absorb glucose and return blood glucose levels to normal
   • 3. Formation of Antibodies
     • Antibodies are proteins that inactivate foreign invaders (bacteria, viruses, toxin) that cause illnesses. When your diet does not contain adequate proteins, your body cannot produce enough antibodies and your immune response is weakened.
       • higher risk of infection and illnesses.
   • 4. Maintaining Fluid Balance
     • Proteins maintain fluid balance by keeping water approximately divided among 3 compartments Intracellular (inside cells) Extracellular (outside cells) Interstitial (between cells) & intravascular (within veins & arteries)
       • About 2/3 of body fluids are kept inside the cells, 1/3 outside. If too much water enter the cells, they might rupture, if too much water leave the cells, they would collapse.
         • When too much fluid moves from the blood vessels into the tissues, or not enough fluid moves from the tissues back into the blood vessels, this fluid imbalance can cause mild to severe swelling (edema) in one or more parts of the body.
   • 5. Transportation
     • some proteins move about in the body fluids, carrying nutrients and other molecules.
       • Lipoproteins ( a complex of lipids and proteins)
         • - transport lipids to the cells of all tissues
       • Hemoglobin (part of red blood cells)
         • Hemoglobin (part of red blood cells)
   • 6. Source of energy when need arises
     • When insufficient carbohydrates and fats are consumed to meet our body’s energy needs, food proteins are broken down as an energy source. In times of famine & starvation, even body proteins such as muscles are broken down to make energy & glucose for brain, lungs & heart.

5. PROTEINS AND ELDERLY

   • Total body protein contained in lean body mass falls with age. Sarcopenia (age-associated loss of skeletal muscle mass, muscle strength & muscle efficiency) Reduces muscle strength, gait and balance, increases the risk of falls and fraility
   • Protein breakdown & synthesis all decrease with advancing age Conditions of ill health, trauma, sepsis and immobilisation may upset the equilibrium of protein synthesis & degradation
     • Important for elderly to maintain an adequate energy & protein intake Important to preserve bodily functions Especially during episodes of ill health when energy requirements rise Minimise protein loss

6. RECOMMENDED DIETARY ALLOWANCE FOR PROTEIN

   • In Singapore, the recommended dietary alllowance for protein is 1.07 gram per kg body weight
     • Children and teenagers have higher protein needs per kg body weight Protein needs also increase during pregnancy (S’pore :+ 9g) during lactation (S’pore :First 6 months +25g, subsequently +19g) Severe physical stress  increase body’s need for protein during illness (infections, fever); after injury (surgery, wound healing, burns) Sports

7. FOOD SOURCES

   • Animal foods: Excellent sources of protein Eggs, meat, chicken, fish, milk, yoghurt, cheese. Plant foods: Legumes, lentils, nuts Legumes like soy bean, kidney bean and all other lentils contain good amount of protein. Rice, bread, pasta, breakfast cereals. Small amounts Negligible amounts in fruits and most vegetables.
   • ANIMAL PROTEIN VS PLANT PROTEIN
     • Animal proteins
       • In general animal proteins (meat, fish, poultry, milk, cheese and eggs) are considered good sources of complete proteins. Animal proteins are also called high quality proteins
         • Complete proteins (or high quality proteins) are those that contain all the essential amino acids in adequate amounts as required by the body
     • Plant / Vegetable Proteins
       • These (grains, legumes, nuts and other vegetables) are incomplete proteins. Also called low quality proteins
         • Incomplete proteins (or low quality proteins), are low in one or more of the essential amino acids The only exception is soy – a complete protein

8. VEGETARIAN DIETS

   • lacto-vegetarian: eats dairy foods but no other animal foods or eggs. ovo-vegetarian: eats eggs but no dairy foods or other animal foods. lacto-ovo-vegetarian: eats dairy foods and eggs but no other animal foods. semi-vegetarian: mostly follows a vegetarian diet but eats poultry and fish occasionally (pesco/pollo). vegan or strict vegetarian: eats no animal foods of any kind. fruitarian: eats only fruits, nuts, honey and vegetable oils.
   • lacto/ovo or semi-vegetarians as they can get high quality proteins from eggs, milk & dairy products and meats
   • Vegans can ensure they get high quality proteins by pairing different plant foods – whereby their proteins complement each other.
     • When grain products are eaten together with legumes, a vegan can get all the essential amino acids in the adequate amounts by the body in his/her diet (adequate lysine and methionine) When nuts/seeds are eaten together with legumes, a vegan can get all the essential amino acids in the adequate amounts by the body in his/her diet (adequate lysine and methionine)
       • 2 incomplete plant proteins when eaten together supplies the amino acid lacking in each other : they complement each other’s lack of specific essential amino acids.
   • Vegetarianism – Pros & Cons
     • Appropriately planned vegetarian diets are healthful and nutritionally adequate
       • Healthier – higher fiber, lower fat especially saturated fats, lower cholesterol. Higher in antioxidants – protect from cell damage & many diseases. Less risk of getting obesity, high blood pressure, heart disease, type 2 diabetes, certain cancers.
     • Vegetarian diets are generally lower in iron, zinc, calcium, vitamin B12 & vitamin D.
       • Children - high nutrient needs for growing, small eaters, fussy eaters, low nutrient stores in their bodies. Teenagers – high nutrient needs for growing. Pregnant women & nursing mothers – high nutrient needs to meet needs of baby as well. Elderly - limited choices with dental problems, small eaters.

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