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The physiology of nutrition The aim of eating: To provide raw materials and energy sources for the body The amount of energy stored in various organs (kJ) Source of E Blood Liver Brain Muscle Fat Glucose/Glycogen 252 1,638 34 5,040 336 Triglycerides 198 1,890 0 1,890 567,000 0 1,638 0 100,800 155 Proteins that can be mobilised Energy balance: calory intake = calory output if +: increased storage if -: utilisation of stores Nutrients: Everything serving as raw material and energy, plus all other molecules required for their utilisation (trace elements, water, ions and vitamins). Bioactive substances: in the absence of these, the metabolic processes would proceed towards undesired directions, and diseases would develop (e.g. dietary fibres, flavonoids, etc.). The well-balanced diet • Isodynamic diet; applicable with certain restrictions only, because: – Loss of amino acids – Fat soluble vitamines – The digesting and absorbing capacities of the GI tract • Recommendation for a healthy adult - The total amount of energy consumed should have the following composition: – Fats: < 30% – Proteins: 10-15% – Carbohydrates: > 55% Nutrient Molecules (1) Water, Inorganic salts Carbohydrates • Direct or indirect sources of energy • When bound to proteins (glycoproteins): structural function – Surface antigens, protective molecules (mucin), most of the enzymes, globular proteins in the plasma, connective tissue • Can be converted to other, biologically important molecules • Dietary fibres: – Water soluble (e.g. pektin) – Water insoluble (e.g. cellulose, hemicellulose, lignin) • Recommendation: 55-60% of the total energy uptake should be provided by carbohydrates. The energy uptake ensured by the ”added sugar” should be less than 10%. The recommended amount of dietary fibres is 30 g/day (about 0.5-1 kg fresh vegetables and fruits; or consumption of 56-84 g oat meal). Functions of the dietary fibres (1) • They delay the absorption of glucose, which increases the sensitivity to insulin – the increase of the blood glucose level is less pronounced after meals • They reduce the blood cholesterol levels – Consumption of 5-6 g water soluble dietary fibres/day may reduce it by 5-10%; – If the plasma cholesterol level is reduced by 1% in the population, it causes a 2% reduction of the mortality of coronary diseases!!! Functions of the dietary fibres (2) • How plasma cholesterol level is reduced? – The dietary fibres adsorb the cholesterol that is secreted into the GI tract – They make lipid absorbtion more difficult from the GI tract – The short-chained fatty acids produced from the dietary fibres inhibit cholesterol production of the body • Dietary fibres have important roles in weightcontrol as well as in reducing the incidence of colon cancers Nutrient Molecules (2) Lipids concentrated energy stores a structural elements of membranes and certain other organelles Essential fatty acids: linolenic and linoleic acid they are the sources of the eicosanoids (containing 20 and 20+ carbon atoms) Recommendation • Lipids should provide less than 30% of the daily total energy intake. • At most 10% of the daily energy intake should be provided by saturated fatty acids. • The daily cholesterol uptake should be less than 600 mg with normal and less than 300 mg with elevated plasma cholesterol levels. Nutrient Molecules (3) Proteins and amino acids Essential components of the tissues and enzymes, (enzymes, transport and storage proteins, structural proteins, protective proteins, hormones, contractile proteins, proteins with not fully known functions) may serve as energy sources • N-balance • Surplus: becomes energy source, protein synthesis is regulated by hormones Essential amino acids (Threonine, Methionine, Valine, Isoleucine, Tryptophan, Phenylalanine, Lysine, Leucine, Histidine [in infants only], Tyrosine {can be synthesized from Phenylalanine}) Nitrogen balance • This is when a person’s daily intake of nitrogen from proteins equals the daily excretion of nitrogen • If +: The protein content of the body increases • If -: The protein content of the body reduces Biological value of the dietary proteins • The proportion of proteins that can be utilised for the biosynthesis of the „own” proteins after absorbtion. Eg.: – – – – – – Mother milk, whole egg: 100 Cow milk: 88-95 Beef: 88-92 Fish: 80-92 Soya beans: 74-78 Corn flour: 49 Recommended daily protein intake • Healthy, adults, on mixed diet: 0.8 g/kg – In the case of 100 kg body mass: 80 g/day • • • • Premature babies: 3.8 g/kg (mother milk must be supplemented with proteins) Infants: 2.2 g/kg 60+ : 0.9-1.1 g/kg (decreased bioavailability) Pregnant and lactating women: 0.8 g/kg – +10 g (pregnancy) – +20 g (at the beginning of the lactation) – +15 g (later phase of lactation) Nutrient Molecules (4) Vitamins: • they are required in small quantities • they are available in the food or provided by bacteria of the gut • they do not give energy but they act as cofactors or enzymes • characteristic deficiency symptoms are seen • these symptoms can be treated by the application of the appropriate vitamin Fat soluble vitamins (1) Deficiencies Vitamin A (Retinol) Formation of visual pigments maintenance of epithelial structures appropriate fetal development Hemeralopia (night blindness) Skin lesions (xerophthalmia) Birth defects Vitamin D (Calciferol) Enhancement of Ca2+ and phosphate absorption from gut Bone and tooth formation Rickets in children (defective bone formation) Osteomalacia in adults Fat soluble vitamins (2) Deficiencies Vitamin E (Tocopherol) Maintenance of RBCs, antioxidant Increased fragility of RBCs Muscular dystrophies Abortion Vitamin K (Naphtoquinone) Enables vitamin K-dependent clotting factor synthesis in liver Failure of blood coagulation Water soluble vitamins (1) Deficiency Vitamin B1 (Thiamine) It is a co-carboxylase, needed for the proper activity of the proteindecarboxylase (thus for decarboxylation - Kreb’s cycle) Beriberi Stoppage of CHO metabolism at pyruvate neuritis (kakke) heart failure (shoshin) • Casimir Funk discovered that the extract of the rice polish cures pigeons suffering from beriberi • He was convinced that he discovered a new class of amines essential for life (vital amines), and the term yielded the now accepted term: vitamine 1929: Nobel prise for the discovery of the „antineurotic vitamine” to Christiaan Eijkman In 40% of the chronic alcoholics vitamin B1 deficiency persists (polyneuropathy); 3-10% of this has the cerebral manifestation (Wernicke encephalopathy). Water soluble vitamins (2) Deficiencies Vitamin B2 (Riboflavin) Flavoproteins in oxidative phosphorylation Fissuring of the skin Glossitis, cheilosis Vitamin B6 (Pyridoxine) Coenzyme for amino acid and fatty acid metabolism Dermatitis Nervous disorders Vitamin B3 (Niacin, Nicotinic acid and nicotinic acid amid) Coenzyme in hydrogen transport (NAD and NADP) Pellagra (3D’s disease) Dermatitis Digestive disturbances Dementia Water soluble vitamins (3) Deficiencies Vitamin B12 (Cyanocobalamin) Nucleoprotein synthesis, RBC production Pernicious anemia Folic acid Nucleoprotein synthesis, RBC production Failure of RBCs to mature “Fetus protecting vitamin” Anemia Vitamin B5 (Panthotenic acid) Constituent of coenzyme A Neuromotor disorders Essential for the health of skin and hair „Burning feet syndrome” Water soluble vitamins (4) Deficiencies Biotin Protein and fatty acid synthesis Dermatitis Transamination Muscle pain Vitamin C (Ascorbic acid) Vital element for collagen synthesis (Prolyl-hydroxylase) Antioxidant Scurvy Infectious diseases of the respiratory tract Failure to form connective tissue Nutrient Molecules (5) Trace elements: (deficiency) (too much) • they are required in minute quantities • Iron (anemia) (haemochromatosis) • Cobalt (part of vitamin B12, pernicious anemia) • Iodine (thyroid hormones, hypothyreosis) • Zinc (dermal ulcers, reduced immune response) • Copper (anemia, impared bone formation, plasma cholesterol level ↑) (Wilson’s disease, brain damage) • Chromium (insulin resistance) • Fluoride (increased risk of caries) Feeding centres: Lateral portion of the hypothalamus feeding centre; if stimulated: evokes eating behavior if damaged: aphagia Ventromedial portion of the hypothalamus satiety centre; if stimulated: food intake stops if damaged: hyperphagia and obesity (glucostat) Energetics Important rules Hess’s law Van’t Hoff’s Law Daily energy request (Total energy expanditure – TEE) • Basal metabolism – 60-75% • Physical activity – 15-30% • Specific dynamic action (DIT) – 5-10% Energy sources: CHO Fat Proteins Energy yield/g in the bomb calorimeter 17 kJ 40 kJ 24 kJ 17 kJ CO2 + H2O CHO 40 kJ FAT CO2 + H2O 24 kJ Proteins CO2 + H2O + NO2 Energy sources: CHO Fat Proteins Energy yield/g in the body 17 kJ 40 kJ 17 kJ Energy yield/g in the bomb calorimeter 17 kJ 40 kJ 24 kJ 17 kJ CO2 + H2O CHO 40 kJ FAT CO2 + H2O 17 kJ Proteins 7 kJ CO2 + H2O + Urea CO2 + H2O + NO2 TEE • TEE = BMR + DIT + Energy expanditure of the muscle activity – BMR: Basal metabolic rate – DIT: Diet-induced thermogenesis • BMR = TEE – DIT – Energy expanditure of the muscle activity • BMR includes: – Energy request of the biosynthesis – Neuronal functions – Maintaining skeletal muscle tone – Circulatory and respiratory work – Secretion activity of glands – Energy request of homeostatic functions – Energy request of thermoregulation Basal Metabolic Rate (BMR) Factors influencing BMR: – sleep: -10% – Cold temperature: +2-5% – Body temperature: every 1ºC increase above 30ºC : +0,5 - 13% – Gender: it is less in women – Age: it increases up to 4-5-years, than begins to reduce (normalised to the body surface area) MENTAL ACTIVITY HAS NO REAL INFLUENCE ON THE BMR Determination: Conditions: Direct calorimetry Indirect calorimetry complete physical and mental rest… Indirect technique (Caloric equivalent of O2: ~ 20 kJ/L) In a 70 kg person about 7100 kJ/day Thyroid hormones and sympathetic activity very effectively increase BMR. Comparing BMR values Normally: 155 – 175 kJ/h/m2 The thermic effect of eating Diet-induced thermogenesis (DIT) • The energy cost of – Food absorption – Food metabolism – Storage CHO: Fat: Proteins: Mixed diet: 4-7% 2-4% 18-25% 8-15% Respiratory Quotient (RQ) RQ = CO2 produced /O2 consumed Glucose C6H12O6 + 6 O2 = 6 CO2 + 6 H2O + 38 ATP 6 CO2/6 O2 = 1 Palmitic acid C16H32O2 + 23 O2 = 16 CO2 +16 H2O +129 ATP 16 CO2/23 O2 = 0.7 RQ values RQproteins RQmixed RQbrain RQstomach = = = = 0.8 0.82 0.98 negative During exercise: RQ ( glycogen degradation) up to 2 When prolonged exercise: RQ ( fat combustion) as low as 0.5 Metabolic acidosis RQ, alkalosis RQ The „Body Mass Index” - BMI • BMI = body weight (kg) / [body height (m)]2 – BMI < 16: Starvation – 20 < BMI < 25: Physiological – 25 < BMI < 30: Overweight – 30 < BMI: Obese Thermoregulation The aim of thermoregulation: to maintain a constant core temperature by matching the amount of heat produced with the amount of heat given away Heat losing mechanisms Direct Indirect Conduction Respiration Convection Evaporation Radiation What determines direct heat loss? Direct heat loss = k × S × (Tskin – Tenv) Heat transfer coefficient Surface area Convection, conduction and radiation may work in both directions (i.e. heat may be gained from the environment). The significance of evaporation (Sweating) Evaporation can ONLY result in heat loss. Evaporation is the ONLY WAY to lose heat if Tenv > Tskin!!!!! May be as much as 2 L/hr Sweat glands have sympathetic cholinergic innervation Heat producing mechanisms (1) Shivering thermogenesis (heat production may be 4-5-times higher than at rest!) Shivering is a high frequency (10-20 Hz) skeletal muscle contraction, when no effective work is performed. Heat producing mechanisms (2) Non-shivering thermogenesis: Metabolism (Sympathetic activity, thyroid hormones, glucocorticoids, insulin, glucagon) Exercise Thermogenin in brown fat (Capable of uncoupling the electron transport chain from the process of making ATP. The result is the production of heat instead of the ATP energy. Thermogenesis occurring in the brown fat is increased by sympathetic activity via β3 receptors) Maintenance of the constant core temperature At external temperatures of approximately 23 °C - 30°C Vasomotor reactions Above 30 °C + Evaporative reactions Below 23 °C + Metabolic reactions ↑ The Big Boss is the hypothalamus (centre of regulation) SET POINT = 37 °C Input from Thermoreceptors Hypothalamus (Both core and shell) Outputs to skin circulation (vasomotor responses), skeletal muscle (shivering, voluntary movements), sweat glands, metabolic changes (via Symp. NS, thyroid glands) brown fat How does the hypothalamus work? (1) Case 1. Response the core temperature is higher than the set point Heat producing mechanisms Voluntary movements Heat losing mechanisms Vasodilatation Sweating How does the hypothalamus work? (2) Case 2. Response the core temperature is lower than the set point Heat producing mechanisms Shivering Metabolic activity Symp.activity, Thyroid hormons Voluntary movements Heat losing mechanisms Vasoconstriction Piloerection Curling up How does the fever develop? NEW SET POINT = 40 °C (!) Endogen pyrogens Hypothalamus (PGE2) Exogen pyrogens Heat producing mechanisms Heat losing mechanisms Vasoconstriction Piloerection Curling up Shivering Metabolic activity Sympathetic activity Voluntary movements How is the fever terminated? SET POINT = 37 °C (again) Aspirin Heat losing mechanisms Vasodilatation Sweating Hypothalamus The comfort zone Q* Q T T T The very essence of thermoregulation Q* Q T T