Learning Objectives - Define the units of nutritional energy, the foods we eat that serve as energy nutrients and their relative energy content.!- Recall the general structures and properties of carbohydrates (sugars, startches) and fats (triglycerides).!- Understand how metabolism is used to derive energy from energy nutrients and the central role of ATP in energy transfer.!- Appreciate the concept of energy balance and the consequences of energy imbalance.!- List the diff. components of energy expenditure and their impact of energy balance.!!Nutrition's Importance in Medicine - Malnutrition-->undernutrition or overnutrition!- Optimal nutrition= defining the optimal levels of various nutrients in our diet for health!- Individual nutrition!!Energy and Life - Everything we do requires energy. This energy comes directly from food that we eat in the form of chemical energy contained in 'energy nutrients.'!- By oxidizing energy nutrients we can derive and store energy.!- The human body is an energy transduction machine!!!Units of Nutritional Energy - Oxidation chemical changes= the same as when burned in air!- calorie= amout of heat to raise T of 1g of H20 by 1degree C!- 1000 calories= 1 kcal = 1 Calorie= 4.1kJ!!Major Classes of Energy Nutrients - Carbohydrates: starches, sugars, 4 kcal/g - Fats: triglycerides and fatty acids, 9kcal/g - Protein: aa's, 4 kcal/g (because we don't oxidize the amide group of proteins-->excrete it as ammonia or urea)!!Carbohydrates - Polyhydroxy (many hydroxyl groups) aldehydes and ketones (CH20)n!- In fruits, veggies, grains= major source of calories in most people's diets!- monosaccharide= basic building blocks= a simple sugar ex. glucose, fructose !!!!!!!!!!!!!!!!!!glucose = 6 Carbon sugar- Dietary carbohydrates:!- most made of monosaccharides joined together by glycosidic bonds!- Disaccharride= 2 monosacc. units !ex. sucrose (gluc + fruc), lactose (galactose + glucose), maltose (2 glucoses)!- Oligosacc= 3-9 monosaccs!- Polysaccharides > 10 monsaccs. ex. starch and glycogen!!!!!!!!!!! - Dietary Fats!- lipids = hydrophobic organic molecules that func. as barriers in membranes, energy metabolites, and signaling molecules!- predom. dietary lipid= fats= triglycerides= triacylglycerols!- backbone of glycerol + esterified to 3 fatty acid chains!- Fatty acids - basic building block of most lipids, single carboxylic head joined to hydrophobic hydrocarbon tail!- General formula= CH3-(CH2)n-COOH!- n> or = 13, long chain fatty acid!- most abundant fa in triglys= long chain fatty aicds of 16-18 C's!- saturated fatty acids= contain no double bonds in the hydrocarbon chain - unsaturated fatty acids= contain one or more double bonds in the hydrocarbon chain!!- Dietary protein!- source of energy, also gives us certain aa's essential for protein synthesis = essential amino acids which we can't synthesize!!- Where does the E in E nutrients come from?!- By oxidizing energy nutrients into H20 and COs, the potential E in the compounds is released!- Oxidation ocurs in a stepwise fashion so we can trap some as chemical energy!- As the molecule gets more and more oxidized, it contains less and less chemical E for us to get!- ATP= the principal currency of E transfer in all organisms!!- Catabolism (breakdown)= metabolic pathways providing energy !- glucose + fatty acids + amino acids --> acetyl CoA--> citric acid cycle--> ATP + H20!- ATP (adenosine triphosphate)= the critical energy intermediate. Has high energy bonds and releasing these sets forth the most E.!Lactose- the energy trapped in the high E bonds of ATP can be used in the cell to perform work!- get ATP from exergonic rxns and use it to do endergonic rxns!!- Metabolic pathways!- Metabolism= all the chemical rxns involved in maintaining the living state of a cell or organism!- is organized in pathways and cycles - can couple favorable w/unfavorable rxns (delta G's [standard free energies] are additive, if NEGATIVE= rxn is favored)!- can obtain E more efficiently in a stepwise rxn!- by regulating key rate-limiting steps in the pathway, the entire pathway can be controlled!!!!!!!!!- not all the E is trapped, the rest of it is released as heat to keep our body temps where they should be!!- Energy Storage -Principle forms: Lipid- triglyceride, carbohydrate-glycogen, protein-no specific storage form, though we'll metabolize protein (esp. muscle protein) for E under starving conditions!- Typical E in person: 15kg in lipids, 0.25 kg in carbs, 6 kg in proteins (in muscles)!= total energy storage= 160,000 kcal (about 95 days)...though this isn't really reality, more like 80 days if we have enough water!!- Energy balance - Components of energy expenditure - Basal metabolic rate= E req. to sustain basic life processes (majority)!- Proportional to lean body mass = total body mass body- fat mass!- BMR increases in response to a number of physio stresses: injury, fever, surgery, infections, and burns - Increased by: being male, caffine, tobacco, thyroid hormones, pregnancy, lactation!- To measure: individ is awake, hasn't eaten for 12 hours, lying down in thermoneutral envi (indirect calorimetry, which measures rate fo O2 consumption and CO2 production)!- Most common= resting metabolic rate (RMR), less stringent and easier to measure, usually higher than BMR!- resting energy expenditure (REE) = extrapolation of RMR over 24 hour (kcal/24hr) - Physical activity= E for physical activity - Thermic effect of food= E req. to digest, absorb, and transport and store food!-is pretty much a constant between people - Adaptive thermogenesis= heat expended to maintain body temp in response to a hot or cold envi (we pretty much ignore this in our envi, is a very small component)!!- Energy imbalance = over a period of time, energy intake doesn't = energy expenditure!intake > expenditure: weight gain/overweight/obesity!expenditure < intake: weight loss!- difficult to lose weight though: ads, food choices, appetite regulation that is evolutionarily set to favor energy
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