Lecture 1.1 - Nutrition, diet and body weight.pdf

Energy: ◦Energy is defined as the capacity to do work. ◦All living things use energy (fuel) constantly to: ‣ Resist entropy (decay and disorder) Constant repair ‣ Support growth ‣ Support the activity of tissues ‣ In the case of m...

Energy: ◦Energy is defined as the capacity to do work. ◦All living things use energy (fuel) constantly to: ‣ Resist entropy (decay and disorder) Constant repair ‣ Support growth ‣ Support the activity of tissues ‣ In the case of mammals to maintain constant body temperature ◦Capacity to perform work (movement) ◦Cells need energy for: ‣ Biosynthetic work - synthesis of cellular components ‣ Transport work across cell membranes - maintenance of ion gradients, uptake of nutrients ‣ Mechanical work - muscle contraction ‣ Electrochemical work - nervous conduction ‣ Osmotic work - kidneys ◦Energy exists in many inter-convertible forms (energy cannot be created or destroyed) Raw materials: ◦Body constituents must be made from basic materials ‣ Derived from diet Essential nutrients ‣ Inter-converted and combined by expenditure of energy Metabolism: ◦Metabolism - the processes which derive energy and raw materials from food stuffs and use them to support repair, growth and activity of the tissues of the body. ◦This requires energy substrates which are catabolised to transfer energy (carbohydrates, lipids, protein and alcohol) ◦This requires substrates to synthesise compounds (anabolism) like protein, but also lipids and monosaccharides, as well as some minerals e.g. calcium in bone. ◦Many processes require cofactors to support metabolic activity (vitamins and some minerals) Chemical bond energy: ◦A chemical bond is a form of potential (stored) energy. ◦All chemical reactions: ‣ Involve breaking and formation of chemical bonds ‣ Breaking bonds releases energy ‣ Making them uses energy ◦Reactions where more energy is released than used are exergonic (outside work - different to exothermic - outside heat) ‣ Needs an intermediate process ‣ The ADP/ATP cycle ◦Reactions where more energy is used than released are endergonic (e.g. anabolism - protein synthesis) Nutrition:  ◦We eat about 500kg of food a year (1-2kg per day), providing: ‣ Energy ‣ Carbohydrate - mostly supplies energy ‣ Protein - energy and amino acids (for synthesis) ‣ Fat - energy and essential fatty acids (lipid membranes, steroid hormones etc) ‣ Vitamins and minerals - essential (vitamins - organic compounds, minerals - ionic) ‣ Water - maintains hydration (cooling, solvent and transport) ‣ Fibre - necessary for normal GI function and supporting gut microbiome Food: ◦Food is made up of a mixture of large molecules containing small nutrient molecules. ‣ Carbohydrates are made up of polysaccharides, disaccharides and monosaccharides Mostly ends up as glucose ‣ Proteins made up of amino acids, and can be essential or non-essential. There are also some non-proteinaceous amino acids e.g. taurine. ‣ Fats containing fatty acids and glycerol (and cholesterol) ‣ Micronutrients - minerals and vitamins ◦Broken down to small nutrient molecules in the gut Micro-nutrients: ◦Essential for life ◦Minerals: ‣ Na+ and K+ (maintains membrane potential) ‣ Calcium (structural and membrane potential) ‣ Fe2+ (oxygen transport) ‣ Others (e.g. Mg2+ and Cu2+) support enzymatic processes ◦Vitamins: ‣ Facilitate metabolic reactions Fat soluble and water soluble vitamins Fat soluble: A, K, D, E Water soluble: C, B group + others (some vitamins like compounds e.g. inositol and choline - previously considered B vitamins) ‣ Deficiency diseases if inadequate intake Recommended daily allowances: ◦Average amount needed per day to maintain good health ◦Depend on age and gender and level of physical activity ◦Increased in pregnancy and lactation ◦Not the minimum required to prevent symptoms and signs of deficiency ◦In UK, RDA is replaced by Reference Nutrient Intake (RDA used for labelling) ‣ Amount which is enough for >97% of population Eatwell guide: ◦B12 is found in animal products ◦Calcium is found in dairy and bread. ◦B vitamins found in carbohydrates.  ◦Vitamin C is found in fruit and vegetables. ◦Iron is found in meats. Metabolism: Blood: ◦Transport nutrients to site of use or for storage. ◦Contains many chemicals ‣ Nutrient from diet on way to tissues for: Utilisation Storage Inter-conversion ‣ Nutrients released from storage on way to utilisation elsewhere ‣ Materials produced in cells for blood itself Proteins, clotting factors Waste products from tissues on way to excretion Blood concentrations: ◦Concentration of most things in blood is constant, but: ‣ Supply from nutrients is fluctuating ‣ Demand for substances very variable ◦Some cells must: ‣ Store nutrients ‣ Interconvert molecules - at variable, but controlled rate Tissues affecting nutrient concentrations: Nutrients and metabolic products in fasting blood plasma: ◦Glucose - 4.2 mmol/L (3.5-5.9 mmol/L fasting) ◦Amino acids - 2 mmol/L ◦Triacylglycerides - 2 mmol/L (0-2mmol/L fasting) - can increase the chance of pancreatitis in adults, and cardiovascular disease ◦Cholesterol - 5mmol/L (a clinical target level) ◦Free (non-esterified) fatty acids - 0.5mmol/L  ◦Lactate and pyruvate -