Chapter 23 Metabolism and Nutrition PDF

Chapter 23 Metabolism and Nutrition Chapter Outline Module 23.1 Overview of Metabolism and Nutrition (Figures 23.1, 23.2) A. Introduction to Metabolism and Nutrition: the energy content in the human diet is measured in terms of heat. 1. The...

Chapter 23 Metabolism and Nutrition Chapter Outline Module 23.1 Overview of Metabolism and Nutrition (Figures 23.1, 23.2) A. Introduction to Metabolism and Nutrition: the energy content in the human diet is measured in terms of heat. 1. The calorie (C) is a measure of heat where 1 calorie is the amount of heat required to raise the temperature of one gram water by one degree Celsius. 2. The kilocalorie is the actual unit of calorie used to measure the human diet where one kilocalorie is the amount of heat required to raise the temperature of one kilogram of water by one degree Celsius. 3. Define metabolism. Metabolism is the sum of the body’s chemical reactions. Summarize the four basic metabolic processes. a. Harnessing the energy in the chemical bonds of molecules obtained from the diet called nutrients that may be used to make adenosine triphosphate (ATP). b. Converting one type of molecule into another for the cell’s synthesis reactions. c. Carrying out synthesis reactions and assembling macromolecules such as proteins, polysaccharides, nucleic acids, and lipids. d. Breaking down macromolecules into their monomers or other smaller molecules. 4. Metabolism occurs through many series of enzyme-catalyzed reactions called metabolic pathways. B. Phases of Metabolism: Catabolism and Anabolism are the two phases with the following characteristics: 1. Describe catabolism. Catabolism is a series of reactions in which one substance is broken down into smaller parts. The process as a whole releases Catabolism energy that the cell can harness to drive other processes. The body uses the Fucose admits following 3 types of nutrient monomers for its catabolism to generate ATP: Fay Copyright © 2019 Pearson Education, Inc. 1  a. Glucose catabolism, the breakdown of dietary and stored carbohydrates, is carried out by every cell in the body. This monomer is the preferred fuel for many cells including those of the brain and liver. b. Fatty acids, mainly triglycerides, are broken down into free fatty acids and glycerol that can proceed into separate catabolic pathways or can be used by the cell for other purposes. c. Amino acids are liberated by catabolic pathways that breakdown proteins. Amino acids can proceed into separate catabolic pathways or can be used by the cell for other purposes. 2. Describe anabolism. Anabolism is a series of reactions in which smaller molecules are combined to make a larger molecule. Cells use smaller molecules to build larger macromolecules such as proteins, nucleic acids, lipids, and carbohydrates. C. Energy Requirements of Metabolic Reactions. Chemical reactions are usually paired such that the energy released from an exergonic reaction (usually a catabolic process) feeds liberated energy into an endergonic reaction (usually an anabolic process) (Figure 23.1). 1. Exergonic reactions release energy, leaving the products with less energy than the original reactants possessed. Most catabolic reactions are exergonic. 2. Endergonic reactions require the input of energy to proceed. The products possess more energy than the reactants. Energy must be added to the reactant side of the equation to satisfy the law of conservation of energy. What types of reactions are endergonic? Most anabolic reactions are endergonic. 3. Explain the relationship between exergonic and endergonic reactions within a cell (Figure 23.1): a. Energy is released from exergonic catabolic reactions. b. This energy is used to fuel the endergonic anabolic reaction of ATP synthesis. c. ATP is broken down in an exergonic catabolic reaction. Copyright © 2019 Pearson Education, Inc. 2  d. The energy from ATP breakdown fuels another endergonic anabolic reaction in the cell. D. Adenosine Triphosphate (ATP) and Phosphorylation: ATP is the main form of energy currency in the cell. The following are characteristics of ATP: 1. ATP is inherently an unstable molecule. Negatively charged phosphate groups repel one another strongly, which places strain on the molecule, making the bonds highly unstable and the molecule reactive. 2. ATP hydrolysis is highly exergonic, but the cell is only able to harness about 40% of the released energy to perform work. 60% of the released energy is lost as heat due to the inefficiency of this exergonic reaction. 3. Harnessed energy from ATP drives cellular processes in the following two ways: (1) Released energy can be used by the cell to directly fuel certain reactions such as muscle contraction. (2) Released energy can be used by the cell in a process called phosphorylation. 4. Define phosphorylation. Phosphorylation is the process where ATP donates a phosphate group to a reactant under the direction of an enzyme. The reactant becomes more reactive, favoring the conversion of the reactant to the desired product. E. Nutrients and ATP Generation: The capability to use the chemical energy in nutrients to drive ATP synthesis is a result of the ability to transfer electrons from one reactant to another called electron carriers. The following characteristics define this type of reaction (Figure 23.2): 1. Oxidation-Reduction Reactions: when fuel is burned its electrons are transferred to from one molecule to another; this is an exergonic reaction that releases energy and heat (Figure 23.2). a. The substance that loses electrons is oxidized, and the substance that gains electrons is reduced. The mnemonic OIL RIG is helpful: Oxidation is loss; Reduction is gain. b. During catabolism of nutrient molecules, they are oxidized and their electrons are transferred to another molecule, which is reduced. The Copyright © 2019 Pearson Education, Inc. 3  flow of electrons from one molecule to another is then used to perform cellular work, including ATP synthesis. 2. Electron carriers are molecules with high electron affinity that accept electrons that are removed from the oxidation of nutrient molecules. Module 15.2 Glucose Catabolism and ATP Synthesis (Figures 23.3–23.8) A. Introduction to Glucose Catabolism (Figure 23.3): 1. Glucose catabolism refers to the reactions that involve the breakdown of a monosaccharide and the use of the chemical energy in glucose’s bonds to drive ATP synthesis. 2. Glucose catabolism has the following two main components, both of which generate ATP: (1) Glycolysis is a series of reactions that occur in the cytosol that splits glucose. (2) The citric acid cycle is a series of reactions in the mitochondrial matrix that continues glucose’s breakdown. 3. Oxidative phosphorylation is a series of oxidation-reduction reactions that take place in the inner mitochondrial membrane that allows the cell to use the energy liberated by glucose catabolism. 4. The electron transport chain (ETC) involves the transfer of electrons during the oxidative phosphorylation process, which leads to ATP synthesis. B. Overview of Glucose Catabolism and ATP Synthesis: A great deal of potential energy is locked in the bonds between atoms of a glucose molecule. Summarize the two types of phosphorylation and the following ways in which ATP can be synthesized by the energy released by glucose catabolism: 1. Substrate-level phosphorylation: A phosphate group is transferred directly from a phosphate-containing molecule (the substrate) to ADP, which forms ATP. 2. Oxidative phosphorylation: The energy from the flow of electrons is harnessed in a process that generates ATP. 3. Glucose catabolism can be divided into the following two broad classes: a. Glycolytic or anaerobic catabolism reactions take place in the absence of oxygen and involved glycolysis or glycolytic catabolism. Copyright © 2019 Pearson Education, Inc. 4  b. Oxidative or aerobic catabolism (cellular respiration) so named because these reactions require oxygen. Both the ETC and citric acid cycle are examples. Cellular respiration refers to the cell’s consumption of oxygen and production of carbon dioxide and water. C. Glucose Catabolism Part 1: Glycolysis: Glucose is broken down is a series of 10 enzyme-orchestrated reactions that takes place in the cytosol. Glucose is split into two 3-carbon sugar molecules called pyruvate. These10 reactions can be condensed into the following two phases each of which contains 5 reactions (Figure 23.4): 1. Energy Investment Phase: consists of 5 reactions that have been condensed into the following three major steps: phosphorylation of glucose and then phosphorylation of glucose-6-phosphate, and cleavage. At the conclusion of this phase: How many ATP have been used? 2 ATP have been used. Two three-carbon compounds, both of which contain a phosphate group, have been generated and are ready to enter the payoff phase. 2. Energy Payoff Phase: consists of the remaining 5 reactions, condensed into the two major steps. The phosphate groups of each 3-carbon sugar from the investment phase are transferred to ADP to yield ATP and each compounds is then oxidized to produce NADH. 3. Overall yield of glycolysis at the end of the payoff phase: two molecules of ATP are spent, four molecules of ATP are synthesized, two molecules of NADH are synthesized, and glucose is split into two three-carbon pyruvate molecules. The net energy yield from splitting a single glucose molecule by glycolysis is two molecules of both ATP and NADH. D. Intermediate Step: The Fate of Pyruvate: The end product of glycolysis is two pyruvate molecules, what happen to these molecules depends on the amount of oxygen available (Figure 23.5): 1. Under anaerobic conditions, pyruvate is reduced to lactate. 2. Under aerobic conditions, pyruvate moves into the mitochondria, is oxidized, and then enters the second step of glucose metabolism, the citric acid cycle. Copyright © 2019 Pearson Education, Inc. 5 E. Glucose Catabolism Part 2: The Citric Acid Cycle (tricarboxylic acid cycle, Krebs cycle). Eight reactions make up the second part of glucose metabolism and represent the beginning of the cell’s oxidative glucose catabolism. These reactions do not require oxygen directly, but require adequate O2 concentrations to proceed. A small amount of ATP is produced by substrate-level phosphorylation (Figure 23.6). 1. Acetyl-CoA proceeds through the citric acid cycle (8 total reactions) through citrate synthesis, first oxidation, ATP synthesis, and second oxidation. 2. Each glucose molecule produces two acetyl-CoA molecules, which turns the cycle twice. The following overall yield per glucose from the beginning of glucose catabolism: Ten NADH molecules (2 from glycolysis, 2 from pyruvate oxidation, and 6 from the citric acid cycle), two FADH2 molecules, and four ATP molecules (2 from glycolysis and 2 from the citric acid cycle). 3. At this point, little energy has been generated but the chemical energy from the bonds in the glucose molecule has been conserved by the transfer of its electrons to NADH and FADH2; these electron carriers can move on to the ETC and ATP synthesis. F. ATP Synthesis: The Electron Transport Chain and Oxidative Phosphorylation. This is the final stage where most of glucose’s potential energy is used to make ATP, which involves oxidative phosphorylation and the following three interrelated processes: the transfer of electrons between electron carriers, the generation and maintenance of a hydrogen ion concentration gradient, and the use of this gradient to drive the release of ATP (Figure 23.7): 1. Electron Transfer and Proton Pumping (Figure 23.7a): more than 15 electron carriers make up the electron transport chain (ETC), which is contained within 4 large enzyme complexes (numbered I – IV) embedded in the inner mitochondrial membrane. Electrons are passed down the “chain” between carriers in the form of hydrogen atoms. 2. ATP Synthesis. Hydrogen ions (H+) have been pumped from the mitochondrial matrix into the intermembrane, creating a steep concentration gradient, and with it an electrical gradient where more positive charges are in Copyright © 2019 Pearson Education, Inc. 6  the intermembrane than the matrix. Chemiosmosis occurs when H+ ions flow through an ion channel across the membrane back into the mitochondrial matrix down the electrochemical gradient. This drives the work of ATP synthesis. ATP synthase is a large protein in the inner mitochondrial membrane that functions as both ion channels with a turbine rotor and an enzyme that catalyzes ATP production. Module 23.3 Fatty Acid and Amino Acid Catabolism (Figures 23.9–23.11) A. Cells are capable of breaking down fatty acids and amino acids in addition to glucose where many of the same metabolic pathways and products are utilized. B. Fatty Acid Catabolism (Figure 23.9) 1. Review of fats in the body: Most fats exists as triglycerides which contain three long hydrocarbon chains or fatty acids linked to a modified sugar, glycerol. Lipolysis is an enzyme-catalyzed process that liberates fatty acids and glycerol. Glycerol is converted to glyceraldehydes-3-phosphate and enters glycolysis. Fatty acids are catabolized to acetyl-CoA by β-oxidation and by products called ketone bodies by ketogenesis. 2. β-oxidation: In cells that can oxidize fatty acids, such as skeletal muscle fibers and cardiac myocytes, fatty acids enter the mitochondrial matrix (Figure 23.9). Each fatty acid is bound to coenzyme A, which initiates a series of reactions called β-oxidations. Fatty acids can be converted into greater amounts of ATP when compared to glucose catabolism. 3. Describe ketogenesis. Ketogenesis is a process that occurs primarily in liver cells that can utilize β-oxidation, where two acetyl-CoA molecules are linked together, under certain conditions, to form one four-carbon molecule called a ketone body. During extreme caloric restriction, carbohydrate restriction, or full starvation, the liver begins to rapidly oxidize fatty acids for energy, which leads to the production of large quantities of ketone bodies. What promotes ketosis and ketoacidosis? The accumulation of ketone bodies in the blood is called ketosis, which can lead to a dangerous lowering of blood pH called ketoacidosis. Copyright © 2019 Pearson Education, Inc. 7  C. Amino Acid Catabolism: Proteins used for catabolism are derived either from the diet or those found already in the cytosol. The following summarizes the fate of protein destined for catabolism (Figure 23.10): 1. Dietary proteins are broken down into amino acid subunits in the digestive tract, which then are absorbed into the bloodstream and delivered to liver cells (hepatocytes). 2. The events of protein catabolism occur in the following sequence of events (Figure 23.10): a. In transamination, the amino group is removed and transferred to - ketoglutarate generating two products: (1) a carbon skeleton and (2) the amino acid glutamate. b. The carbon skeleton can be converted into a variety of compounds, which can then be oxidized. c. In the mitochondria of the hepatocyte, glutamate undergoes oxidative deamination. Some of the amino groups removed as ammonia are used in the synthesis of new amino acids. The remaining ammonia molecules are removed by the urea cycle, which forms urea that is then eliminated by the kidneys in urine. Urea is formed when two ammonia molecules are combined with carbon dioxide. Module 23.4 Anabolic Pathways (Figures 23.12–23.14) A. Introduction to the Anabolic Pathways: Anabolism or biosynthesis serves many vital purposes. The following are introductory features of anabolism: 1. Anabolism serves the following vital purposes: (1) nutrient storage, (2) nutrient synthesis, (3) structural element synthesis, (4) synthesis of special molecules such as FAD and NAD+. 2. The body stores nutrients when nutrient intake from the diet exceeds the amount of energy immediately required, or when the body needs a ready supply of nutrients to oxidize for maintaining metabolic homeostasis between meals. Copyright © 2019 Pearson Education, Inc. 8  3. The two main nutrient energy storage forms are glycogen, which consists of glucose units, and adipose, which is made up of mostly triglycerides. B. Glucose Anabolism: Glycogenesis and gluconeogenesis are the two anabolic processes involving glucose (Figures 23.12, 23.13): 1. Glycogenesis, the storage of excess glucose obtained from the diet, has the following structural and functional features (Figure 23.12): a. Glycogen is a molecule composed of thousands of glucose units. b. Summarize glycogenesis. Glycogenesis is the synthesis of glycogen. It involves a series of enzyme-catalyzed reactions, found mostly in hepatocytes and skeletal muscle fibers, which add glucose units to the growing storage molecule. c. Summarize glycogenolysis. Glycogenolysis is the catabolic process that cleaves glucose units off of the storage molecule to maintain blood glucose homeostasis. 2. Gluconeogenesis is a mechanism by which glucose molecules can be synthesized from noncarbohydrate molecules once glycogen supplies have been exhausted. Hepatocytes and specific kidney cells convert three and four carbon compounds into glucose. The following are potential sources of this process (Figure 23.13): (1) Glycerol from triglyceride catabolism, (2) Pyruvate and lactate can be converted, (3) Intermediate compounds from the citric acid cycle can be converted, and (4) Specific glucogenic amino acids can be converted. 3. Fatty acids cannot be converted into new glucose molecules. C. Fatty Anabolism: Synthesis of fatty acids resembles β -oxidation in reverse although it involves a completely different pathway, enzymes, and manufacturing location. 1. Summarize lipogenesis. Lipogenesis is the process used to synthesize fatty acids. This process takes place in the cytosol under the direction of the enzyme fatty acid synthase, which catalyzes the reaction that progressively lengthens fatty acids chains, two carbon units at a time. Copyright © 2019 Pearson Education, Inc. 9  2. Glycerol and fatty acids are derived from amino acids and glucose, not just from dietary sources. 3. Excess amino acids are also converted into triglycerides by a similar mechanism. D. Amino Acid Anabolism: Amino acids are not stored to any significant extent in the body’s proteins. 1. The body is capable of synthesizing 11 of 20 amino acids, 9 amino acids must be obtained from dietary sources. 2. Synthesis involves reactions that add an amino group to a carbon skeleton molecule such as α-ketoglutarate, pyruvate, or oxaloacetate. 3. Cells synthesize a limited number of proteins and excess amino acids are converted to other molecules for storage. Module 23.5 Metabolic States and Regulation of Feeding (Figures 23.15) A. Metabolic States: The following two basic metabolic states ensure that the cells are provided with energy at all times. These states differ in terms of their proximity to feeding and the metabolic reactions that predominate (Figure 23.15): 1. Discuss the absorptive state. The absorptive state occurs right after feeding, from the time ingested nutrients enter the bloodstream and can last up to 4 hours. As nutrients are absorbed from the small intestine, the following processes occur: oxidation of nutrients, glyconeogenesis, lipogenesis, and synthesis of amino acids into proteins. 2. Discuss the postabsorptive state. The postabsorptive state begins once nutrient absorption is complete usually after the 4-hour absorptive window has ended. Although variable, the body is usually in this state in late morning, late afternoon, and most of the night. Anabolic processes slow or stop and processes such as ketogenesis, gluconeogenesis, glycogenolysis, lipolysis, glucose sparing dominate. B. Regulation of feeding is controlled by a variety of hormonal and neural signals that stimulates and/or inhibits feeding-related nuclei found in the hypothalamus: Copyright © 2019 Pearson Education, Inc. 10  1. The hypothalamus houses the satiety center and hunger center that control homeostatic variables associated with feeding. 2. Long-term regulation of feeding is primarily hormonal and regulated by the hormones leptin and ghrelin. 3. Short-term signals can also inhibit or stimulate feeding. Insulin decreases food intake. Feeding stretches the stomach walls and initiates the release of gastrointestinal hormones such as cholecystokinin. Both stimulate the vagus nerve to indirectly suppress the hunger center and decrease the release of hunger-related neurotransmitters. Concentration levels of certain molecules in the blood can stimulate or inhibit these hypothalamus centers. Module 23.6 The Metabolic Rate and Thermoregulation (Figs 23.16–23.18) A. Metabolic rate is the total amount of energy expended by the body to power all of its processes. Heat is generated as a byproduct of these collective reactions, which is a vital source of body heat and the maintenance of temperature regulation or thermoregulation (Figure 23.16). 1. The metabolic rate is measured in units of heat or calories. Heat is eventually lost from the body to the surrounding environment. 2. Thermogenesis is the process by which energy is converted to heat, which makes heat production a method for the measurement of energy expenditure. 3. Define the basal metabolic rate (BMR). BMR is defined as the minimal rate of metabolism for an awake individual or the “energy cost of living.” The body continues to use energy even when at rest. 4. Many factors affect the body’s energy expenditure so it varies from BMR regularly (Figure 23.16). B. Heat Exchange between the Body and the Environment: Heat moves when gradients are present. Heat produced by the body’s metabolic reactions is exchanged with the environment by the following 4 mechanisms (Figure 23.17). Describe each mechanism. 1. Radiation is the process that transfers heat from one object to another through electromagnetic waves. Copyright © 2019 Pearson Education, Inc. 11  2. Conduction is the process where heat is transferred from one object to another through direct contact. 3. Convection is the process in which heat is transferred through a liquid or gaseous medium. 4. Evaporation is the process by which water changes from a liquid to a gas. C. Thermoregulation: Body Temperature Regulation. Thermoregulation or regulation of body temperature is a key homeostatic variable that must be maintained within a narrow range to ensure all systems function properly (Figure 23.18). 1. Body temperature is maintained within a relatively constant range: 35.8 to 38.2 oC (96–101oF) with an average of 37.5 oC (99.5 oF), which reflects core body temperature. 2. Regulation of body temperature is regulated by a negative feedback loop that responds to an increase in body temperature with the following sequence of events (Figure 23.18a). Complete each part of this loop: a. Stimulus: Body temperature increases above normal range. b. Receptor: Thermoreceptors in the skin and the hypothalamus detect increased body temperature. c. Control center: The heat-loss center of the hypothalamus is activated. d. Effectors/response: Blood vessels in the skin dilate, and sweat glands release sweat. e. Homeostatic range and negative feedback: As body temperature returns to the homeostatic range, the hypothalamus stops stimulating the effectors, which decreases the responses. 3. Regulation of body temperature also responds to a decrease in body temperature, which triggers the following negative feedback loop events (Figure 23.18b). Complete each part of this loop. a. Stimulus: Body temperature decreases below normal range. b. Receptor: Thermoreceptors in the skin and hypothalamus detect decreased body temperature. Copyright © 2019 Pearson Education, Inc. 12  c. Control center: The heat-promoting center of the hypothalamus is activated, which sends signals to the effectors. d. Effectors/response: Blood vessels in the skin constrict, shivering in skeletal muscles is triggered, and the metabolic rate increases. e. Homeostatic Range and negative feedback: As body temperature returns to the homeostatic range, the hypothalamus stops stimulating the effectors, which decreases the responses. 4. Impaired Temperature Regulation: When the core temperature moves outside the homeostatic temperature range, significant disruptions in all body systems can result, such as hypothermia, hyperthermia, heat stroke, or fever. Module 23.7 Nutrition and Body Mass (Figures 23.19, 23.20; Tables 23.1– 23.4) A. Overview of Nutrients: A nutrient is a molecule obtained from food that the body requires for its metabolic processes. The 5 main categories of nutrients include the fuel molecules (1) carbohydrates, (2) proteins, and (3) lipids as well as molecules called (4) vitamins and (5) minerals, and structural molecules obtained from the diet, such as cholesterol. 1. Macronutrients include carbohydrates, proteins, and lipids because they are required in relatively large amounts thus make up the bulk of the diet. 2. Micronutrients include vitamins and minerals because they have much lower requirements in the diet. 3. Essential nutrients are molecules that the body is incapable of producing and must obtain from dietary sources. B. Macronutrients include carbohydrates, lipids, and proteins. The following tables explores their dietary sources, recommended dietary allowances (RDA) and their functions in the body (Tables 23.1, 23.2): 1. Carbohydrates in the diet consist of monosaccharides, disaccharides, and polysaccharides. a. Fiber is a group of polysaccharides that are not fully digestible by humans. Insoluble fiber, found in whole grains, fruit skins, and bran, Copyright © 2019 Pearson Education, Inc. 13  passes through the digestive tract virtually unaltered. Soluble fiber is partially digested by bacteria in the colon into compounds that can be absorbed into the blood stream. b. A well-rounded diet should consist of 45–65% carbohydrates, most of which should be polysaccharides. 2. Lipids ingested from the diet include triglycerides, cholesterol, and certain vitamins. a. Saturated fatty acids are hydrocarbon chains without any double bonds that include mostly animal-derived products. Unsaturated fatty acids contain one double bond (monounsaturated) or more double bonds (polyunsaturated) that are found commonly in plant-derived products. b. Essential fatty acids are those fats that the body is unable to synthesize and must be obtained from the diet. c. Fats, mostly unsaturated fats, should constitute about 30% of the daily caloric intake. 3. Proteins and the 20 amino acids used in their construction are important molecular fuels, structural molecules, and enzymes. It is currently recommended that 10–35% of daily caloric intake comes from protein-rich foods (Table 23.2). Non-essential amino acids include 11 amino acids that can be synthesized from carbon skeletons while essential amino acids include the 9 amino acids, which cannot be synthesized and must be obtained from dietary sources. C. Micronutrients include vitamins and minerals that are not used as fuel but play critical roles in nearly all of the body’s physiological processes (Tables 23.3, 23.4): 1. Vitamins (vital amines), 13 organic compounds to date, that are required for the body’s functions (Table 23.3). Vitamins A, D, E, and K are fat-soluble while vitamin C and the B vitamins are water-soluble vitamins. Copyright © 2019 Pearson Education, Inc. 14  2. Minerals: a mineral is any element other than carbon, hydrogen, oxygen, nitrogen that is required by living organisms. These are not used as fuels but are important components in many physiological processes (Table 23.4). D. Structural Lipid: Cholesterol is not oxidized for fuel. It is important to many anabolic processes in the body. Cholesterol is modified to produce vitamin D, steroid hormones, and bile salts. It is also an important structural molecule in the plasma membrane. A discussion of how cholesterol is processed by the body follows (Figure 23.19). 1. Cholesterol Processing by the Liver: Cholesterol is found in animal-based foods including meats and dairy products. The liver is capable of synthesizing 85% of required cholesterol with the diet contributing only 15%. 2. Lipoproteins are carrier proteins that provide transportation for cholesterol in the bloodstream. Several types of lipoproteins include very low-density lipoproteins (VLDLs), lipoprotein lipase, low-density lipoproteins (LDLs), and high-density lipoproteins (HDLs) (Figure 23.19). 3. Disorders of Cholesterol Processing: Hypercholesterolemia is an elevation of the total cholesterol in the blood, which occurs when dietary intake exceeds the 15% of total requirement for cholesterol. E. Diet and Body Mass: Body mass refers to the amount of matter in the body; body weight is more commonly used, and refers to the force exerted on body mass by gravity (Figure 23.20). 1. Body Mass Index (BMI) is an equation that accounts for height and provides a reference range that helps to determine relative body mass. 2. Energy balance or nitrogen balance is the difference between energy intake and energy expenditure, which determines the rate an individual gains or loses body mass. 3. Healthy Diet: A healthy diet meets an individual’s needs in terms of micronutrients, macronutrients, essential amino acids, and other molecules such as cholesterol. MyPlate is a resource provided by the USDA in 2011 that depicts the proportions of the types of foods that should make up a nutritious meal (23.20). Copyright © 2019 Pearson Education, Inc. 15 4. Obesity: Individuals who have a body mass index of greater than 30.0 are considered obese. Obesity increases the risk for many diseases, such as type 2 diabetes, coronary artery disease, cancer, hypertension, and osteoarthritis. Copyright © 2019 Pearson Education, Inc. 16