Human Nutrition Chapter 6

CHAPTER 6: PROTEINS AND AMINO ACIDS      Amino Acids (AA) o Contain nitrogen (amine group) o 20 amino acids  8 are essential, some may become conditionally essential (ex: histidine) o Are joined together by peptide bonds to form proteins  2 aa = dipeptide  3 aa = tripeptide  >3 aa = polypeptide Building Protein: o Amino acids along strand chemically attracted to or repelled from each other  Create a coil shape o Spots along the coil attracted / repelled  Globular structure or fibrous structure o Each protein unique in structure Protein synthesis o Proteins:  DNA (genetic sequence) determines the amino acid sequence in proteins  Different sequences account for:  Genetic diseases  Ex: sickle cell disease Protein digestion o stomach  Gastic acid denatures protein and pepsin (enzyme) cleaves some peptide bonds o Small intestine lumen  Pancreatic enzymes cleave polypeptides to di and tri peptides o Brush border membrane  Enzymes cleave di- and tri- peptides to single amino acids Protein absorption o Intestinal cells absorb amino acids and some di- and tri- peptides and release them into the bloodstream  Absorbing larger peptides may contribute to food allergies (immune response) Carried to liver - used or released back into the blood to be taken up by body cells Body can reconnect amino acids to make proteins Body can use aa for energy if necessary Functions of proteins o Growth and maintenance  Structure, new tissue, repair o Enzyme action  Ex: growth factors, insulin o Immune function  Antibodies o Protein transport  Ex: protein malnutrition and edema o Acid base balance o Blood clotting o Energy (secondary function)  No storage form of amino acids Protein utilization o Used to build proteins o Converted to other small nitrogen-containing compounds  Ex: vitamins (tryptophan —> niacin) o Converted to other amino acids o After removal of amino group  Gluconeogenesis  Carbon skeleton — glucose — blood  Lipogenesis: carbon skeleton — fat for fuel or storage o Amino acids are wasted when  Energy is lacking  Protein is overabundant  An aa is over supplied (supplement)  Diet has too few essential aa  Low protein quality Protein in food: o Found in all 4 food groups o Recommendations for intake:  DRI: 0.8g/kg body weight:  women: 46g/day, men: 56g/day  DRI minimum amount: 10% total energy  DRI maximum amount: 35% total energy Protein Quality and Quantity o Malnutrition, infections, state of health can increase need for protein o Two factors influence protein quality  Digestibility (improved by moist heat)  Animal protein: >90% absorbed  Plant protein: 70-90% absorbed  Amino acid composition o o o     High quality proteins contain ample amounts of all essential amino acids o Complementary proteins  2 or more proteins whose amino acid structures supply the essential amino acids missing from the other  Need complementary proteins in the same day  Legumes limiting in methionine and tryptophan  Grains limiting in isoleucine and lysine  Together they supply all 4 amino acids Measuring Protein Quality o Protein digestibility-correct amino acid score (PDCAAS)  Reflects protein digestibility  Proportion of amino acids provided o Scale of 0-100  Egg white, ground beef, chicken products, fat free milk, tuna = 100  Soybean protein = 94  Wheat protein = 25  Combining complementary proteins can increase score Nitrogen Balance o Nitrogen intake compared to nitrogen excretion  Through urine, faces, skin, sweat, bodily fluids o Depends on size and stage of growth  Equilibrium: normal healthy adult  Need 0.8 grams protein/kg body weight  Positive: growing child, pregnant woman  Negative: surgery patient, astronaut Protein energy malnutrition     Marasmus Kwashiorkor <2 yrs age 1-3 years age Total diet deficiency Protein deficiency Slow chronic Rapid onset, acute Sever weight loss Some weight Muscle and fat loss Some muscle mastin <60% weight for age 60-80% weight for age No edema Edema No fatty liver Fatty liver Anxiety, apathy Apathy, irritability Appetite varies Loss of appetite Hair and skin problems Hair and skin problems World: 33 000 children die every day, many are malnourished North America: PEM associated with chronic disease, poverty, eating disorders  Protein Excess o o o o o  Excess: >35% calories from PRO High intakes of animal protein  Associated with obesity  Increased intake of saturated sat  Kidney and liver problems in experimental animals  More bone mineral loss with high intakes of purified protein  More calcium lost in urine  Evdence mixed for effect of meat protein on Ca High intakes of protein  Worsen existing kidney disease in humans  Increase work of the kidney to excrete nitrogen wastes: amine group of amino acids is excreted as ammonia or urea  Does this lead to long term problems?  Effective treatment for kidney problems = reduce protein intake High protein diets for weight loss  Protein used for energy and making lgucose  Must remove amino acid group and excite it as urea via kidneys  Low CHO: if <130g CHO/d, then no glycogen stores, and ketotonic  Body fat — ketone bodies for energy  Blood glucose made from  Dietary amino acids (after means  Muscle protein (when post-absorptive) and this results in muscle wasting High protein, low CHO diets  Initial rapid weight loss due to more water loss from body, loss of body fat and muscle mass long term  Diet high in saturated fat?: long term cardiovascular disease risk  Diet high in cholesterol  Diet often low in some vitamins and minerals (ex: calcium) and low in fibre Controversy 6: o Comparing diets: vegetarian and omnivorous (consume meat) o Vegetarians: plant based foods, some or all animal foods eliminated o Vegan: only food from plant sources o Lactoovo-vegetarian: eats dairy and eggs, no flesh or seafood o Lacto-vegetarian: eats dairy, no eggs, flesh or seafood o Ovo-vegetarian: eats eggs; no milk products flesh or seafood o Partial vegetarian: no red meat or limited quantities o Pesco-vegetarian: no red meat or poultry o Fruitarian: eats raw/dried fruit, seeds, nuts o Macrobiotic diet: progressively eliminates foods — brown rice, herbal tea, water  Malnutrition and death Pros of Vegetarianism: Pros of Omnivorous Diet   Reduced risk of disease (obesity, heart disease, diabetes, hypertension, cancer) o Diet is high in vegetables, fruit, fibre, phystochemcials, its/mis o Lifestyle often excludes smoking and alcohol, and emphasizes physical activity Lower fat diet and leaner body composition o Maintain healthier body weight o Better control of caloric intake due to fibre-rich bulky foods    Growth is optimal o Complete, more digestible protein o Protein from meat, eggs, milk products Maybe easier to meet additional requirements for pregnancy, illness, etc. Vit B12, Vit D, calcium, iron, and zinc intakes are usually adequate Chapter 7: Vitamins    Vitamins: essential, non-caloric organic nutrients Needed in very small amounts Cofactors (helpers) in cell functions o Do not need to memorize the RDA, AI or UL amounts CLASSIFICATION  Fat soluble: vitamins A D E K o Dissolve in lipid o Require bile for absorption o Transported in lymph o Stored in tissues e.g., liver, adipose o May be toxic in excess  Caution with supplements o Vitamin A:  Chemical forms: retinol (retinal, retinoic acid), b-carotene (can be converted to vitamin a but need 6x amount)  DRI: RDA700-900 ug/day  Functions  Gene expression  Vision  Epithelial tissue  Immune defences  Growth of bone  Reproduction  Food sources  Beef liver, fish oil, milk, dark orange and green vegetables  Beta-carotene  Vitamin a precursor  Plant sources: brightly coloured  Effective antioxidant  May reduce risk of chronic disease o Eye diseases (macular degeneration) o Cancer  Deficiency is prevalent in developing countries  Symptoms: o Blindness, night blindness, xerosis o Impaired bone growth, easily decayed teeth o Immune function lowering o Keratin lumps on skin  Developed rice with added vitamin A  Toxicity symptoms o Stunted growth, muscle/bone soreness, headaches o Edema, fatigue, blurred vision o Anorexia, nausea, diarrhea o Skin disorders, rashes, itching o Liver damage, enlargement of spleen  Beta carotene toxicity: yellowing of the skin  Other sources of vitamin A:  Retinoic acid as a drug, directly applied to the skin results in rapid turnover of skin cells o Retin-A: acne; Renova: anti-wrinkle o Highly toxic: serious birth defects if taken during pregnancy o Supplementing Vit. A does not help acne o Vitamin D  Chemical name: cholecalciferol  Functions:  Regulation of blood calcium and phosphorus levels, important for bone formation and maintenance  Workings of the brain, heart, stomach, pancreas, skin and reproductive organs  Immune system (stimulates maturation of cells)  Functions as a hormone  RDA = 15 ug/d (600IU)  Food sources: fortified milk and margarine, eggs, butter, fish  Sunlight: UV radiation converts precursor molecule (cholesterol backbone) in skin  Duration specific to race: facial area for 15 min 3-7x/week  3h for dark skinned  Manitoba latitude: April to Oct; use liver stores in winter  Risk of skin cancer, not vit. D toxicity with ++  Deficiency:  Rickets and osteocalcin (bone disease in children and adults respectively)  ? Research: may increase risk of high blood pressure, some cancers, Type I diabetes, heart disease, rheumatoid arthritis, IBD, MS  Risk of deficiency increase with age  Lower intake, housebound, lower ability to activate vitamin D  Vitamin D toxicity  Vitamin with most risk of toxicity; UL: 100 ug/day (4000IU)  Symptoms:  Appetite loss, nausea/vomiting, increased thirst & urination, severe psychological depression  With long term toxicity:  Calcium deposits in heart, blood vessels, lungs & kidneys  death o Vitamin E  Chemical name: tocopherol  Alpha (gold standard), beta, delta, gamma  Function:  Acts as antioxidant in cell membranes o Integrity of cells (lung, RBC, WBC) exposed to high oxygen concentrations  DRI = 15mg/day  Upper limit = 1000mg/day  Food sources:  Widespread in foods  Vegetable oils, fruit & veg, fortified cereals and grains, meats and alternatives, milk products  Deficiency:  Rare, as it is widespread in foods, body stores, cells recycle vitamin E) o Erythrocyte hemolysis (premature infants) o Weakness, impaired reflexes (muscle and nerve function) – oxidative damage o Caused by fat absorption and storage problems  Toxicity is rare  Nausea, fatigue, GI distress, blurred vision  Increased risk of bleeding when combined with anticoagulant medications  400 IU/day: increased risk of death from all causes o Vitamin K  Functions: blood clotting and bone protein synthesis  Anticoagulant medications interfere with Vit. K and blood clotting  Recommendations: DRI: men 120 and women 90 ug/day    Sources:  Bacterial production in colon o Affected by absorption problems/illness o Antibiotics decrease production  Food sources o Green, leafy vegetables, cabbage families o Liver, eggs, milk o Beans/legumes Deficiency is rare  Newborns – need supplements at birth as they have sterile GI tracts  Taking meds that kill intestinal bacteria  Problems with fat absorption  Symptoms: easy bruising, hemorrhaging Toxic in excess is rare  Infancy, pregnancy: taking vitamin K supplement  Symptom: jaundice – RBCs break & release pigment (bilirubin) CLASSIFICATION  Water soluble: vitamin C, B vitamins