u Section 1: Protein metabolism
u Section 2: Protein requirements and vegetarian diets
u Section 3: Consequences of Obesity
Copyright By PowCoder代写 加微信 powcoder
Proteins and Amino Acids
Section 1:Protein Metabolism
Amino Acid Structure
u The building block of proteins = amino acid.
u Carbon atom bound to four chemical groups
u The amino group contains to a nitrogen atoms.
u About 20 amino acids are commonly found in proteins.
u Nine (9) amino acids = essential or indispensable amino acids.
u Amino acids made in the body = non-essential or dispensable amino acids.
Transamination
u Transamination is the process by which an amino group from one amino acid is transferred to a carbon compound to form a new amino acid.
Fig 6.4: In this example, the amino acid alanine transfers its amino group to alpha-ketoglutarate, resulting
in the formation of a new amino acid, glutamate.
By this reaction, a non-essential amino acid can be converted to another non-essential acid; or an
essential amino acid can be converted to a non-essential amino acid.
Conditionally essential amino acids
uConditionally essential or indispensable amino acids
uTyrosine à phenylalanine.
uIf intake of phenylalanine drops = tyrosine essential.
Shown here is a list of essential amino acids, and nonessential amino acids, including those that may be conditionally essential under certain circumstances.
You do NOT have to memorize the names of the essential and non-essential amino acids, with two exceptions. You should remember that lysine and methionine are the essential amino acids that are the most difficult to obtain.
Protein Structure
u peptide bond.
u Many amino acids linked together = polypeptide or protein.
Digestion of protein
u Dipeptides, and tripeptides
u They enter the enterocyte via transporters.
u Dipeptides and tripeptides are broken down to amino acids.
u The individual amino acids enter the blood stream
Protein Digestion and Food Allergies
u Food allergies
u protein is absorbed intact à immune system is stimulated u when food is consumed againà allergic reaction
u Symptoms: vomiting & diarrhea; rash or hives; difficulty breathing; drop in blood pressure
u Anaphylaxis: severe reaction
u Common allergens that require labelling:
u Egg, milk, mustard, peanuts, crustaceans and molluscs, fish, sesame seeds, soy, sulphites, tree nuts, wheat and
u Ingredients list must indicate source using common name:
u Whey protein (milk)· sugar · natural flavours
u Whey protein · sugar · natural flavours Contains milk
Protein in the Body
Limiting amino acids
Transcription and Translation
Gene expression:
Nutrients can control gene expression: Zinc intake increased expression of metal binding proteins
Vitamin A regulates expression involved in the development of immune cells
Vitamin D regulates calcium transpot proteins
PUFA regulate lipid metabolism Glucose influences insulin expression
Before amino acids are used for energy, they are deaminated.
Deamination produces
Ammonia is converted to urea in the liver.
Urea is transported to the kidney for excretion.
Protein function
u Structural proteins: e.g. collagen in bone u Enzymes
u Transport proteins
u Protective proteins e.g. skin, antibodies u Contractile proteins: e.g. muscle
u Hormones e.g. insulin u Fluid regulation
u pH regulation
Protein Deficiency
u Protein Deficiency:
u Kwashiorkor
u Disease the first child gets when second is born
u First child is weaned off breast milk to a low protein diet
u Diet sufficient in energy but low in protein
u Swollen belly: fluid accumulation in tissue because of low blood proteins and lipid accumulation in liver because of lack of transport proteins
u Marasmus
u Starvation – lack of energy and protein
Celiac Disease
u Intolerance to gluten
u Found in wheat, rye, barley
u Diagnosis: detection of antibodies to gluten & biopsy of the small intestine to confirm damage to villi
u Treatment: Avoidance of all gluten
u Celiac disease increases a person’s risk of gastrointestinal cancers, low bone
density, and other autoimmune disorders
u Gluten-free foods and diets have become a fad, leading to self diagnosis and persons not eating gluten-containing products
u Problem: diagnosis for celiac disease not possible as antibodies to gluten disappear when gluten-containing foods are not eaten
Section 2: Protein Requirements & Vegetarian Diets
Determining Protein Requirements: Nitrogen Balance
u Protein is the only macronutrient that contains nitrogen
u Excretion = losses in urine, feces, & skin
u Nitrogen (g) X 6.25 = Protein (g)
u Nitrogen balance occurs when nitrogen intake equals nitrogen excretion
Determining nitrogen balance
Nitrogen intake
Nitrogen Excretion*
Nitrogen balance
Intake -lowest
Intake -low
Intake -Moderate
Balance – best estimate of requirement
Intake –Moderately high
= intake but greater than at moderate intake
Intake –High
= intake but greater than at moderately high intake
*Feces + Urine + Skin
AMDR: 10-35% kcal from
• range to allow for different dietary patterns and preferences
• 10% will meet the RDA
• >35% protein à higher in %kcal from saturated fat
(protein from animal sources) and lower in % kcal from carbs than recommended
Canadian average intake: 2015-CCHS-Nutrition: 17% kcal protein
Figure 6.20
Determining Protein Requirements: Indicator Amino Acid Method
u For protein synthesis to take place all indispensable or essential amino acids are required at an adequate dose
u This dose = protein requirement
u Use an indicator AA with a C-13 label
u When protein intake is too low to provide all essential amino acids C-13 isotope appears in breath as 13CO2 because AA is used for energy rather than protein synthesis
u As protein intake increases 13CO2 decreases
u Protein intake at which 13CO2 levels off = protein requirement
Determining Protein Quality
u Quality is determined by the limiting essential amino acid
u Complete protein – contains all essential amino acids in proportions that support protein synthesis
u Animal-based proteins
u Incomplete protein- missing
essential AA
u Most plant-based proteins
u Scoring System:
u Digestible Indispensible Amino Acid
u Takes into account amino acid composition and ileal digestibility
u Digestibility: feed protein to human or animal (pig) and determine how much AA is unabsorbed at the end of the small intestine (ileum)
u e.g. If 10% of amino acid is detected at the end of small intestine, then 90% is absorbed and digestibility is 0.90
Reference protein:
Amino acid pattern that meet
requirements
1) Infants
2) 2) child: 6 month to 3 years
3) Older children, adolescents, adults
Protein Rating:
Canadian Food Inspection Agency
Protein Rating = Protein in a Reasonable Daily Intake X Protein Efficiency Ratio (PER)
Animal Feeding Study: Protein Efficiency Ratio:
Wt gain when fed test protein
Wt gain when fed reference protein
Protein Complementation
Foods from complementary sources should be consumed during the entire day
Vegetarian Diets
u Vegetarians: no animal products
u Lacto-ovo-vegetarians: eggs & milk included but no fish, meat, poultry u Vegans: avoid all animal products
This Photo by Unknown Author is licensed under CC BY-SA
Required Textbook Reading
Critical Thinking:
Scientific Evidence for the Benefits of a Vegetarian Diet Pg. 285 & A46
Be sure that you can answer the questions in the textbook that accompany the reading
Section 3:
Consequences of Obesity
Guidelines for a Healthy Body Weight
u BMI: body mass index = weight (kg)/height(m)2
u Most common assessment tool for assessing healthy body weight u Body weight classifications:
uBMI < 18.5 Underweight uBMI 18.5 -24.9 normal uBMI 25-29.9 overweight uBMI >30 obese
Know these numbers.
Obesity increases the risk for:
u Type-2-diabetes
u Cardiovascular disease u Cancer
Integration of carbohydrate and fat metabolism (Review from Week 6: Lipids)
Post prandial
Spares glucose for the brain
Between meals
Obesity à ↑↑FFA release and ↑↑inflammation u There is always a steady release of free fatty acids (FFA) from adipose tissue
to provide the body with a constant source of energy
u The levels of FFA are proportional to the amount of adipose tissue present u Weight gain à Expansion of size of cells
u Individuals with high levels of adiposity release more FFA than lean individuals u These higher levels of free fatty acids à changes in lipid and glucose
metabolism
u Inflammation increases with adiposity
u Large mass of adipose tissue à zones of hypoxia (low oxygen levels) à cell death à recruitment of immune cells à inflammation à secretion of inflammatory proteins to the rest of the body
Obesity increases the risk for type-2-diabetes
FFA = free fatty acids
Obesity increases the risk of cardiovascular disease
Increased VLDL secreted by liver
Increased free fatty acids (FFA)
Increased uptake by the liver
VLDL = very low density lipoproteins rich in triglycerides
Normal lipoprotein metabolism: VLDL is released by the liver and enters the blood stream to deliver fatty acids to tissue.
1) The enzyme lipoprotein lipase (LPL) hydrolyzes the triglycerides and fatty acids enter the tissue. Some cholesterol is also released at the same time and is taken up by HDL and returned to the liver.
2) As TG are depleted from the VLDL particle it is converted to an intermediate density particle (IDL)
3) The IDL particle is further depleted of TG it becomes a LDL.
4) LDL is taken up by the liver and metabolized.
Abnormal Lipid Metabolism
When VLDL levels are high there are the usual lipid transfers (steps 1-3) that occur in normal metabolism.
But there are also some atypical transfers:
Step 4: Cholesterol from HDL, instead of being taken up the liver is transferred to VLDL particles, resulting in cholesterol-depleted HDL which is rapidly cleared from the blood resulting in low HDL levels.
Step 5: TG from VLDL are transferred to LDL resulting in TG-enriched LDL. These TG enriched LDL are acted on by hepatic lipase, which removes the TG and results in the formation of a particle called a small dense LDL (sd-LDL).
This sd-LDL is atherogenic, increasing the risk of cardiovascular disease.
Lipid Triad
u High VLDL – serum triglycerides u Low HDL
u High sd-LDL
u Associated with increased risk of cardiovascular disease
F3.1:Obesity and Cancer
Which common cancer is missing?
Prostate cancer
Obesity and Cancer
Metastasis
u Disease characterized by a series of genetic mutations that result in a cell that:
u de-differentiates (no longer functions as intended)
u becomes proliferative (grows uncontrollably; does not respond to “stop”
u can not repair its damaged DNA
u becomes resistant to programmed cell death (apoptosis)
u Apoptosis = method the body uses to get rid of damaged cells it cannot repair
Obesity and Cancer:
u Cancer Development u Insulin & estrogen
u Growth factors that promote cell growth u Insulin
u Stimulates the growth of cells
u Suppresses apoptosis u Estrogen
u Stimulates the growth of breast tissue
u In postmenopausal women, stimulates the growth of breast tumours u Circulation in the blood:
u Bound to sex hormone binding globulin (SHBG) u Less bioavailable (less stimulation of cell growth)
u Free estrogen – not bound to SHBG u More bioavailable (more stimulation of cell growth)
Obesity and Cancer
Psychological and social consequences of obesity
uWeight stigmatization refers to negative attitudes, mistreatment and discrimination based on weight status, particularly negative attitudes toward people with obesity.
Weight stigmatization
u What percentage of people who attempt weight loss fail?
u “In the current environment, people who are not devoting substantial conscious effort to managing body weight are probably gaining weight.” Peters 2002
程序代写 CS代考 加微信: powcoder QQ: 1823890830 Email: powcoder@163.com