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Week 5: Proteins (Functions of Protein in the Body :check: (Acid-Base…
Week 5: Proteins
Functions of Protein in the Body :check:
As antibodies
When the body detect an antigen, it produces antibodies, which is designed to fight against the foreign invaders
With insufficient dietary protein, the body cannot maintain its army of antibodies to combat infectious diseases
(antigen) A substance that triggers the formation of antibodies.
Source of energy and glucose
At times of starvation or inadequate carbohydrates intake, proteins are sacrificed to provide energy and glucose
Tissue proteins are broken down to make amino acids available for energy or glucose production (known as gluconeogenesis), enabling normal blood glucose level, at the expense of losing lean body tissue
As hormones
Hormones are messenger molecules
Some are made from proteins (whereas some, such as estrogens and testosterones are made from lipid cholesterol)
Released into the body when there are changes that challenge the body (i.e. pancreas release insulin when glucose level is high; whereas when glucose level is low, pancreas releases glucagon)
Fluid Balance
Proteins are found in the cells primarily and in the plasma (blood without red blood cells)
Due to its large molecular size, it doesn’t cross the walls of the blood vessels usually
During critical illness or protein malnutrition, blood vessels become “leaky” and plasma proteins move into the spaces between the cells
BUT Protein attracts water, therefore fluid accumulates, causing swelling (aka edema)
Edema includes
Inflammation and critical illnesses leading to excessive protein losses
Liver disease hence, inadequate protein synthesis
Inadequate protein intake
As enzymes
Break down substances during digestion
Used to build substances (e.g. bones)
Transform into another substance (e.g. amino acids into glucose)
Acid-Base Balance
Acts as a buffers by accepting and releasing H+ ions
When the bodily fluid is acidic (low pH with high concentration of H+ ions), proteins, which contain negative charges, attract H+ ions. Therefore increasing the pH
Blood’s acid-base balance is tightly regulated to maintain a pH within 7.35 – 7.45
Anything out of this range will lead to coma and death, by denaturing the proteins
Denatured protein is useless due to the change in shape
Structure materials
Major structural component of all the body’s cell
Creates building blocks of muscles, blood, and skin
Give the strength and shape to skin, tendons, membranes, muscles, organs and bones
Transportation
Some proteins carry nutrients and other molecules in the body fluids
Some transport proteins stay inside the cell membranes as behave like “pumps”
Vegetarian Diet :check:
Types
Health Benefits
Weight control
Lower blood pressure
Lower cholesterol level
Lower incidence of heart disease
Lower rate of certain cancers (colorectal, prostate cancer)
Vitamin/Mineral Deficiencies in Vegetarians
Protein
Iron
Zinc
Vitamin D
Calcium
Riboflavin (B2)
Vitamin B12
Dietary Recommendations for Vegetarian
Choose a variety of foods, including whole grains, vegetables, fruits, legume, nuts, seeds, and if desired, dairy products and eggs
Choose whole, unrefined foods often and minimize the intake of highly sweetened, fatty and heavily refined food
Choose variety of fruits and vegetables
If animal foods such as dairy products and eggs are used, choose lower-fat dairy products and use both eggs and dairy products in moderation
Protein Use During Physical Activity – and between Times : :check:
Protein Used in Muscle Building
During activity: synthesis of protein is suppressed
Hours of recovery post activity: protein synthesis accelerates beyond normal resting levels
High intake of protein and/or carbohydrate after an activity
Enhances muscle synthesis
Insulin is secreted, with food intake
Body adapts and builds the molecules, cells and tissues it requires for the next activity.
Repeated activity, with slight overload, triggers adaptation by
Protein dismantling
Protein synthesizing
The physical work of each muscle cells:
Acts as a signal for the DNA and RNA to start producing the kind of proteins that will best support that work
Stimulates muscle protein synthesis
Greatly inhibits muscle protein breakdown
Protein Used as Fuel:Contributes only 10% of the total fuel used, both during activity and during rest
Like fat and carbohydrate, muscles speed up their use of amino acids for energy during physical activity
Endurance athletes use large amounts of all energy fuels, including protein
During performance, they usually consume adequate protein due to increased food intake
Factors Affecting Protein Usage
Intensity
Duration
Endurance athletes who trained more than 1 hour a day and engaged in aerobic activity of moderate intensity and long duration
Glycogen stores may be depleted by the end of their workouts
Body will be more dependent on protein for energy
Anaerobic strength training
Needs more protein for muscle building
Higher protein requirements than sedentary people, but not as high as the protein intakes many athletes consume
Does not use protein for energy
Diet
Protein- and Fat- rich, less CHO
Fats cannot be convert into glucose, hence protein will also be broken down
Carbohydrate- rich, adequate energy
Carbohydrates spare protein from breaking down to make glucose when needed
Health Effect of Protein :green_cross:
High Intake based on types of sources
Cancer from animal based protein
Adult Bone Loss
increases calcium excretion, which contributes to bone minerals loss
compromise bone health → Osteoporosis
Heart disease from animal based protein, rich in saturated fat
Weight gain
High protein food often high in fat
Protein-Energy Malnutrition (PEM)
2 types
Marasmus – result from of severe deficiency of protein, energy, vitamin and mineral
Chronic: caused by long-term food deprivation; characterized in children by short height for age (stunting)
Kwashiorkor – result from inadequate protein intake or infections
Acute: caused by recent severe food restriction; characterized in children by thinness for height (wasting)
Over consumption by exceeding 35% of energy intake
May overburden the kidneys’ capacity to excrete nitrogen wastes (i.e. urea)
From High protein diet high in animal proteins that is likely to be low in plant-based foods
Usually low in fiber, some vitamins (vitamin C, E and folate), minerals (magnesium and potassium) and phytochemicals
Increase risks of dehydration if inadequate fluid intake
More fluids are required to dilute and excrete urea
Kidneys use body water to excrete urea
Increase urinary calcium loss
Leading to loss of bone mass and increased risk of osteoporosis
Due to amino acids supplementation
Amino acid toxicity
From High protein diet high in animal proteins (which includes cured meat)
Higher in saturated fats and cholesterol
Increases risk of cardiovascular disease and cancer
Nitrogen Balance: A method to determine protein needs
:check:
3 states
Positive Nitrogen Balance :Protein intake greater than losses
Eating more protein doesn’t build additional body protein; an individual needs to be in a situation require a positive nitrogen balance for this to happen
Occurs in
Pregnancy
Recovery stage after illness/injury
Growth
Negative Nitrogen Balance
Protein intake less than losses
Occurs in
Inadequate protein intake
Conditions such as illnesses
Bed rest
Protein Balance (Equilibrium):Energy intake is sufficient to prevent utilization of protein for energy
Occurs in healthy adults with adequate protein & energy intake
Recommended Intakes of Protein :check:
Protein = 10 – 35% of total calories intake
0.8grams per kilogram of healthy body weight per day (0.8g/kg/day) for healthy individual
Higher for infants and children
RDA takes into the consideration of:
Replacing worn-out tissue
Higher for larger people
Needs for building new tissues during growth
Higher for infants, children, adolescents, pregnant and lactating women
should come from mixed quality (both high- and low- quality sources)
Alongside with adequate carbohydrates and fat to provide sufficient energy and other nutrients
for Physically Active People:Adequate protein (10 – 20% of kcal)
Chemical structure of Protein :check:
(consists of) Amino acids (AAs) containing nitrogen that makes protein chemically different from other macro nutrients
Structure
a carbon
an amino group(NH2)
a acid group (COOH)
a hydrogen
A side group (R):is a unique chemical structure that differentiates one AA from another
Maybe similar, forming special classes that engage in various enzymatic reactions in the body
Acidic amino acids
Basic amino acids
Branched-chain amino acids
(AAs) Joined together by peptide bonds
Dipeptide – 2 AA joined by peptide bond
Tripeptide – 3 AA joined by peptide bond
Oligopeptides – 4 to 10 AA joined by peptide bond
Polypeptides – > 10 AA joined by peptide bond
Has 20 different types, categorized as
Non-Essential:body can make these amino acids as long as there is sufficient nitrogen
Conditionally essential: a non-essential AA becomes essential under special circumstances such as critically ill
Essential: those the body cannot make or cannot make in sufficient quantity, must be provided in the diet
Digestion and Absorption :check:
Mouth
Stomach
Pancreas
Small Intestine
Liver
Large Intestine
Little dietary protein is present in feces
AAs are absorbed into the portal vein and transported to the liver
AAs enter the general bloodstream
Pancreatic and small intestine enzyme protease breaks polypeptides to tripeptides, dipeptides and amino acids
Small intestine enzymes tripeptidase and dipeptidase break tripeptides and dipeptides into amino acids (absorbed)
Protein is further digested by enzymes released by the pancreas into the small intestine
Hydrochloric acid (HCl) activate stomach enzyme pepsin
(Pepsin) breaks protein into smaller polypeptides
Chewing and crushing moisten protein-rich foods and mix them with saliva to be swallowed
Protein Quality: determines how well children grow and how well adults maintain their health :check:
2 types
High quality protein (aka complete protein) – provide adequate essential amino acids required to support body’s function
Most food from animals and soy and chia seeds provide complete protein
Low quality protein (aka incomplete protein) – doesn’t offer adequate essential amino acids needed to support body’s function.
protein in plant food is incomplete, it lacks one or more of the essential amino acids
Plants also offer less protein per weight/measure of food
To improve quality of proteins, many people combine plant-protein foods to have different complementary AA patterns
Complementary proteins: two or more proteins whose amino acid assortments complement each other in such a way that the essential amino acids missing from one are supplied by the other
Influenced by 2 factors
Digestibility
Depends on
Proteins’ source
Better digestion: animal proteins
Less digestible: plant proteins except for soy and chia seeds
Other foods eaten with it
Amino Acid Composition
must contain the 9 essential amino acids and adequate nitrogen-containing amino groups to synthesize non-essential amino acids
Protein synthesis is limited when the diet provides inadequate essential amino acids
Body makes whole proteins only
If one amino acid is absent, the others cannot form a “partial protein”
Limited amino acid refer to an essential amino acid supplied in less than the amount required to support protein synthesis
Essential Amino Acids likely to be limiting
Lysine
Methionine
Threonine
Tryptophan
Biological Value (BV):
a measurement of protein quality
based on how much of the protein is absorbed in the human body to convert into body tissue protein.
the more amino acids are absorbed by the body for protein synthesis, the higher is the biological value of the food
Determined by nitrogen retained in the body in comparison to the amount of nitrogen content of the food protein
expressed as a percentage of the protein nitrogen that has been digested and absorbed
Higher nitrogen retention = Higher BV: When a food’s amino acid pattern matches closely to the amino acid pattern of body protein
Lower nitrogen retention = Lower BV: when a food’s amino acid pattern matches poorly to the amino acid pattern of body protein
