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Nutrition and Metabolism Calories • A Calorie is a unit of energy – Measures how much heat could be released by completely burning a given amount of material • The average adult requires around 2000 Calories a day – The exact rate at which we burn calories is called the metabolic rate Calories in Food • Carbohydrates and Proteins have 4 Calories per gram • Fats have 9 Calories per gram – This is why our body uses fat as a long-term energy storage material – This is also why fat tastes delicious: it’s a very calorie-rich food! • Fun fact: alcohol has 7 Calories per gram! Metabolism • Metabolism is a combination of two processes: anabolism (building up of materials) and catabolism (breaking down of materials) – Growing new cells and proteins is anabolism – Burning glucose for energy is catabolism • When not active, you are at your basal metabolic rate (BMR) Basal Metabolic Rate • BMR is affected by: – Age (decreases with every decade past 30s) – Muscle mass (more skeletal muscle, more calories burned) – Thyroid activity and iodine intake (thyroxine increases BMR) • Activity above basal levels contributes substantially to your overall calorie use – Exercise burns calories! Exercise and Metabolism • Exercise is very healthy to be able to do regularly – Increases muscle mass, which increases BMR – Increases use of cholesterol and saturated fats, so they don’t clog your arteries – Sweating helps balance your sodium • Blood cholesterol is measured as HDL and LDL levels, often called “good cholesterol” and “bad cholesterol” – HDL (High density lipoproteins) transports lipids like saturated fats and cholesterol to liver for processing • Exercise increases HDL levels – LDL (Low density lipoproteins) transports lipids to fat cells for storage Anabolism and Catabolism • A major example of both anabolism and catabolism is a process called gluconeogenesis – The production of blood glucose • Glycogen is made of glucose, so breaking it down to glucose is pure catabolism • Proteins and lipids can be disassembled and reassembled into glucose through anabolism – Amino acids release ammonia when this happens Excess Nutrition • An excess of nutrients above what is needed to make more cells and perform cellular respiration causes the body to store extra materials – Excess glucose stored as glycogen (glycogenesis) – Excess glucose and fat also stored as fat (lipogenesis) – Protein cannot be stored Lipid Metabolism Nutrient Storage • People have genetic differences in how they form and store fat – Some people break down fat more easily than others (lipolysis) – Fat is also stored in different places in the body • Due to its high calorie density, storing fat is vital for life – Pictured is Lizzie Velasquez, who has a genetic condition where her body literally cannot form fat – If she were to stop eating for more than a few hours she will die (once her glycogen runs out) Nutrient Deficiencies • If insufficient carbohydrates or lipids are eaten, the body digs into its reserves • The body also lowers the metabolic rate to try and slow the loss of nutrients – Prevents starvation • Insufficient protein poses serious health risks because protein cannot be made from fat or sugar, so protein is taken out of the muscles Nutrients and Dieting • Due to sociocultural forces, being “thin” is currently conflated with being “attractive” by many people – This has led to fats and “carbs” having a negative connotation since they may result in fat buildup • Can often lead to eating disorders – Please note that having a high metabolic rate is a better indicator of health than body weight or BMI (body mass index) • Ironically an increasing proportion of people in the US are also obese due to high-sugar diets Hunger Effect • Hunger is a complex effect in the body mediated by the hypothalamus, and affected by ghrelin, leptin, cortisol, glucagon and other hormones, as well as psychological factors – “7PM? Well it’s dinnertime then.” • Diabetics who inject insulin after a meal often report being very hungry again soon, because their blood sugar has crashed – Processed sugars are unhealthy often because they cause a large insulin release, a blood sugar crash, and a new feeling of hunger – The large amount of insulin also ensures that fat cells absorb a lot of the glucose Hunger and Stress • Stress (Sympathetic nervous system and cortisol) both block hunger • Ghrelin is released by the parasympathetic nervous system in response to food stimuli (even thoughts) – This allows you to eat even when you’re stressed – Also, mmm, donuts… Who’s Hungry? • Next week: last week of new material! – Monday: Kidneys – Wednesday: Reproductive Systems – Friday: Review day!