Proteins

Food proteins provide the amino acids necessary for building and maintaining body tissue

Protein balance, both with in the body and in the diet, is essential to life and health

The quality of a protein food, and its ability to meet the body’s needs, is determined by the composition of amino acids

Protein is 16% nitrogen

• These are the building units of protein. They contain nitrogen, carbon, hydrogen and oxygen.
• Two types of protein in the body are tissue protein and plasma protein

Two chains linked together is a dipeptide


Polypeptide is many chains linked together.

• Could be 100 or more chains linked together

• -All protein is made upof amino acids
• -All protein chains arejoined by a peptide bond

Amino acids are named for their chemical nature.

There are 20 common amino acids which are vital to human life and health

• Indispensable amino acids- Nine amino acids –
• The body can not manufacture these, must come from diet.

• -Histidine
• -Isoleucine
• -Leucine
• -Lysine
• -Methionine
• -Phenlalanine
• -Threonine
• -Tryptophan
• -Valine

Balance is the relationship between intake and output of substances in the body

Protein Balance- Proteins being broken down into amino acids is called catabolism

Resynthesized of amino acids into proteins is called anabolism

The body maintains how much protein is in tissues, plasma and balanced with protein intake

Nitrogen balance – indicates how well its tissues are being maintained- intake of protein in diet vs amount of nitrogen excreted in urine –also known as state of equilibrium or protein balance

1g urinary protein (nitrogen) = digestion and metabolism of 6.25 g of protein

Positive nitrogen balance- takes in more protein than excretes- storing extra protein in tissues

• Negative nitrogen balance- takes in less than excretes- In children protein deficiency
• can cause growth retardation

• Primary tissue building- Largest portion
• except for water

Additional body functions

Energy system- back up source for energy

• Water balance – Plasma protein, especially
• albumin help maintain water balance

• Metabolism- Protein helps through enzymes,
• transport agents, and hormones

• Body defense system – Protein helps build
• white blood cells or lymphocytes and antibodies as part of the body’s immune system to defend

• Types of food proteins – Food contains a mixture of proteins that complement each
• other- Key to balanced diet is variety

• Complete proteins – Protein food that contain all essential amino acids, primarily
• animal source, eggs, milk and cheese

Incomplete proteins – Protein food that are missing one or more of the nine indispensable amino acids, seeds, vegetables, fruits

Complementary protein- put the puzzle pieces together plant and animal


Types of vegetarian diets

• Lacto-ovo vegetarians – Eggs and dairy ok
• Lacto-vegetarians – Dairy ok, no eggs
• Ovo-vegetarians – Eggs ok, no dairy
• Vegans - No eggs or dairy, no animal products at all

Vegan diets do not have adequate intake of various nutrition

Not enough protein, calcium, phosphorus, zinc, selenium, Vit D, Vit B, and riboflavin

For the most part this diet is a cheap and safe approach to prevent diabetes, cardiovascular disease, stroke, dementia, age related eye disease, GI disease and cancer

• Mouth
• – Mechanical part of digestion is chewing

Particles are mixed with saliva and passed on to the stomach as a semisolid mass

• Proteins are large and complex- All enzymes
• needed for break down of protein are stored in an inactive form called proenzymes or zymogens. Can not store in active form or will break down walls of the stomach and intestines

Stomach

• Pepsin
• – Main gastric enzyme, stored as pepsinogen,
• hydrochloric acid converts to pepsin. Begins splitting the links of proteins and amino acids into short chains called peptides.

• Hydrochloric acid – converts pepsinogen to pepsin and also begins unfolding and denaturing of the complex protein chains. When they are unfolded it makes them
• more available for enzymatic action

Rennin – Gastric enzyme in infancy and childhood- Important to digestion of milk. Rennin with Ca act on the casein of mild to produce a curd. Rennin prevents milk moving too fast from stomach to small intestines

• Small intestine – protein digestion starts in the acid environment of the stomach and
• is finished in the alkaline environment of the intestines.

• Pancreatic secretions
• -Trypsinogen converts to Trypsin – activated by enterokinase, works on large polypeptides and produced small polypeptides and dipeptides

• -Enterokinase is secreted by the duodenum as food enters from the stomach
• -Chymotrypsinogen converts to Chymotrypsin action is the same as trypsin

-Procarboxypeptidase converts to carboxypeptidase action is attacks the acid carboxyl at the end of the peptide chain

• Intestinal secretions – Glands in the intestinal wall produce two more protein splitting
• enzymes to complete the digestion process
• -Aminopeptidase attacks nitrogen containing peptide chain and releases amino acids one at a time producing free amino acids and peptides

• - Dipeptidase final enzyme that completes the task by breaking down remaining dipeptides
• into two free amino acids

Protein requirements: influencing factors

Tissue growth – fetal growth, infant growth, lactation, adolescent growth and development


Dietary protein quality – Four basic measure to determine protein quality

Chemical score (CS) – value derived from amino acid pattern of the food

Biological Value (BV) – Based on nitrogen balance

Net Protein Utilization (NPU) – Based on the biological value and the degree of the food protein’s digestibility

Protein efficiency ratio (PER) – based on weight gain of growing test animal in relation to its protein intake


Illness or disease – fever and catabolism (increased tissue breakdown), increased body’s need for protien

Protein-energy malnutrition- (PEM) –

• - Poor nutrition
• - Disease
• - AIDS
• - Cancer
• - Liver Failure

• Kwashiorkor – Common 18 – 24 month old- taken
• off breast because of new baby and put on high carbohydrate diet. Kwashiorkor is a Ghanian word
• that refers to a disease that takes over the child when the second child is born

Marasmus – Very emaciated, low body fat, Chronic form of protein deficiency – basic starvation

• - High in saturated fats
• - High risk for cardiovascular disease
• - Kidneys have to work overtime to rid the body of excess nitrogen
• - Excess protein increase calcium losses in the bone when dietary calcium is inadequate