ENERGY What Is Metabolism? - PowerPoint Presentation

ENERGY

What Is Metabolism? Metabolism is the sum of all chemical reactions taking place within the cells in the body. The chemical reactions follow a metabolic pathway in which the product of one reaction is the starting substance for the next reaction Each chemical reaction produces a change in energy, as a new bond is formed or old bonds are broken. For example, the forming of new bonds when glucose is stored as glycogen requires energy, whereas the breaking down of glycogen to provide glucose releases energy. Energy can be produced without oxygen ( anaerobically ) or with oxygen ( aerobically ) depending upon the available fuel and amount of oxygen present in the cell.

What Is Metabolism? Metabolism never stops, but continues to adapt and shift as needed. Glucose is the main energy nutrient that keeps metabolism going, but the other macronutrients, fatty acids and amino acids, also contribute to metabolism Metabolism takes place within cells. The mitochondrion is the key site of aerobic metabolism; aside from red blood cells, almost all body cells contain mitochondria. The fluid portion of the cell ( cytosol ) is where anaerobic metabolism takes place in red blood cells. Other organelles contribute in different ways to metabolism.

What Is Metabolism? The liver plays a central role in metabolism After nutrients have been absorbed, the liver determines the metabolic fate of these nutrients. Metabolic processes in the liver convert amino acids, monosaccharides, glycerol, and fatty acids to usable or storable forms of energy. Metabolism is a series of chemical reactions. Anabolic reactions require energy; catabolic reactions produce energy. Anabolic reactions use energy to combine simpler molecules into more complex molecules (for example, single amino acids combine to form larger proteins). Catabolic reactions generate energy to fuel anabolic reactions, breaking down large molecules into simple structures that can be used by the body for energy, recycled for individual parts, or excreted (for example, glycogen molecules hydrolyzed to yield smaller glucose molecules).

What Is Metabolism? Enzymes and hormones regulate metabolism. Enzymes and coenzymes allow metabolic chemical reactions to occur fast enough to maintain normal body function. Most metabolic reactions each require a different enzyme. Hormones can regulate anabolic and catabolic reactions. Hormones released when blood glucose rises influence whether enzymes are activated or deactivated to control metabolic pathways. (For example, insulin controls the metabolism of glucose within cells.) Glucagon, epinephrine, and cortisol can influence metabolism.

How Does ATP Fuel Metabolism? The body uses food for fuel after macronutrients have been disassembled and built into new compounds, then transformed into a molecule called adenosine triphosphate (ATP) Adenosine triphosphate is the cell’s energy source. Creating ATP requires the body to use up some ATP in the process ATP is made up of adenine, ribose, and three phosphate groups; the energy is stored in the bonds connecting the phosphate groups to each other. When energy is needed, one of the bonds connecting the phosphate groups is hydrolyzed, releasing a phosphate and a large amount of energy. The resulting molecule is called adenosine diphosphate (ADP) The body must continually produce ATP to provide for energy needs.

How Does ATP Fuel Metabolism? ATP can be regenerated from ADP and creatine phosphate. Creatine phosphate ( PCr ) , formed in muscle cells when creatine is combined with phosphate, is a high-energy source that can be used for ATP. The phosphate can be released from PCr and added to ADP to form ATP. Energy is released when the phosphate bond is broken, providing the fuel needed to restore ATP. Creatine supplements can increase performance of short-duration, high-intensity athletic activities ATP must be produced through anaerobic and aerobic metabolic processes once the available ATP and creatine phosphate in the muscle cell is exhausted. Anaerobic metabolism produces more ATP than aerobic processes but is limited in use (high-intensity activities of short duration). Aerobic metabolism produces less ATP per minute but can continue indefinitely (low-intensity activities of long duration). When demand for ATP is greater than what the metabolism can supply, the activity slows down or comes to a halt.

How Do the Macronutrients Provide ATP? Carbohydrates, proteins, and fats fuel the production of ATP by entering the metabolic pathway at some point in the stages of metabolism. Carbohydrate metabolism can generate ATP anaerobically and aerobically. Glucose is transformed into energy after entering a cell through glycolysis , the reaction of pyruvate to acetyl CoA , the tricarboxylic acid (TCA) cycle , and the electron transport chain. In the first step, glycolysis transforms glucose to pyruvate. Glycolysis is a ten-step anaerobic, catabolic pathway taking place in the cytosol of the cell. One six-carbon glucose molecule results in two, three-carbon molecules of pyruvate and two molecules of ATP. The initial step in glycolysis requires ATP. Phosphate is transferred from ATP as glucose enters the cell, forming glucose 6-phosphate and ADP; the glucose 6-phosphate continues through nine additional reactions until pyruvate is formed at the completion of the pathway.

Glycolysis

How Do the Macronutrients Provide ATP? Pyruvate to lactate : The metabolic conversion of pyruvate to lactate happens in any human cell. As an example, during strenuous exercise pyruvate is reduced to lactate to prevent buildup of hydrogen ions. In some situations, lactate is not produced fast enough; the buildup of hydrogen ions reduces pH in the muscle cell, leading to the “burning” sensation in muscles after exercise. When lactate leaves the muscle cells it is sent into the blood, eventually arriving in the liver where enzymes convert it back to pyruvate. Pyruvate is then transformed into glucose through the Cori cycle The glucose is then available for release back into the blood where it is picked up by the muscle to be used again.

Anaerobic catabolism: Pyruvate Lactate Aerobic catabolism: Pyruvate Citric Acid Cycle Pyruvate has 2 Possible Fates:

How Do the Macronutrients Provide ATP? Glucogenic amino acids to pyruvate: Eighteen of the 20 amino acids are glucogenic . They can be transformed into pyruvate and other TCA cycle intermediates that can enter gluconeogenesis and produce glucose. If amino acids are to be used for energy, they are transformed into either acetyl CoA or TCA molecules. Ketogenic amino acids are converted to acetyl CoA. Glucogenic amino acids are degraded to pyruvate, converted to acetyl CoA, and then enter the TCA cycle. Glucogenic amino acids can be a major source of blood glucose when the diet is lacking in carbohydrates. Amino acids will come from either the diet or from sacrificed muscle cells.

How Do the Macronutrients Provide ATP? Glycerol to pyruvate: Dietary fat (triglycerides) is a more concentrated source of kilocalories and yields about six times more energy than either carbohydrates or proteins. Both glycerol and fatty acids are used for energy, but in different ways. Only glycerol is glucogenic and can contribute to blood glucose levels. Glycerol produces very little energy compared with glucose, amino acids, or fatty acids. Glycerol can enter the main pathway at two distinct points: Glycerol can enter glycolysis and become pyruvate + ATP. Glycerol can be taken up by the liver cells and converted to glucose through gluconeogenesis. The body’s need for glucose is the determining factor.

How Do the Macronutrients Provide ATP? Pyruvate is then transformed into acetyl CoA . The molecules of pyruvate formed during glycolysis enter the mitochondria, where a carbon is lost and a molecule of coenzyme A is attached. Coenzyme A attaches to the remaining two carbons from pyruvate, forming a two-carbon acetyl CoA. The remaining carbon combines with oxygen, forming carbon dioxide that is then expelled through the lungs as waste. Once acetyl CoA is formed, it can either enter the TCA cycle or be transformed into a fatty acid and stored as fat.

How Do the Macronutrients Provide ATP? Fatty acids to acetyl CoA : Before they can be used for energy, fatty acids are hydrolyzed from triglycerides by lipolysis ( lipo = fat, lysis = break apart). An enzyme called hormone-sensitive lipase in the adipose tissue catalyzes the reaction. Beta-oxidation reactions disassemble fatty acids inside the mitochondrion. Beginning at the carboxyl end of the molecule, fatty acid is taken apart two carbon fragments at a time; the carbon pairs are joined by another CoA and converted to acetyl CoA. New acetyl CoA and a shorter fatty acid chain are formed until all carbons have been oxidized. Hydrogen and electrons are released as each pair of carbons is removed from the fatty acid chain; the hydrogen atoms join two coenzyme hydrogen carriers, which then unload the hydrogen atoms in the electronic transport chain.. The important components are the fatty acid chain, coenzyme A, ATP, and the carrier molecule (carnitine). Fatty acids are considered ketogenic (keto = ketone, genic = forming), not glucogenic, which means fatty acids can be used to produce ketone bodies, which are used as backup fuel for the brain and nerve functions when glucose is limited.

How Do the Macronutrients Provide ATP? Amino acids to acetyl CoA: Six of the twenty known amino acids are either only ketogenic or both ketogenic and glucogenic . Leucine and Lysine first undergo transamination with the TCA acid alpha-ketoglutarate , accepting the amino group that is transferred Ketogenic amino acids generate acetyl CoA and, depending on body requirements, can be changed into fatty acids or ketone bodies.

How Do the Macronutrients Provide ATP? The function of the TCA (tricarboxylic acid) cycle is to gather electrons from carbons in the energy nutrients. During the TCA cycle, energy stored in acetyl CoA bonds is transferred to two coenzyme hydrogen ion carriers to be released in the electron transport chain. One molecule of acetyl CoA enters the cycle, at which time the CoA is removed and the two remaining carbons are combined with oxaloacetate (a four-carbon molecule), forming citrate. Seven further reactions culminate with the formation of oxaloacetate as the last molecule, at which point the cycle begins with the next molecule of acetyl CoA. Two carbons, along with eight hydrogen atoms and their electrons, are removed during the TCA cycle; in total, four molecules of coenzymes, carbon dioxide, and water are released during each turn of the TCA cycle.

How Do the Macronutrients Provide ATP? In the fourth stage, the electron transport chain and oxidative phosphorylation produce the majority of ATP. The primary purpose is to assemble the majority of the ATP cells need to fuel bodily actions through a process called oxidative phosphorylation. A series of protein complexes located in the inner mitochondrial membrane make up the electronic transport chain. These protein complexes ( flavoproteins and cytochromes ) act as carrier molecules to transport electrons generated during glycolysis, the TCA cycle, and fatty acid oxidation along the chain. An electron passes from one protein complex to the next until reaching oxygen; oxygen accepts the electron and it binds with two molecules of hydrogen (forming water). Protons separate from the hydrogen atoms in the coenzymes as the electrons pass along the chain, gathering into the intermembrane space of the mitochondria; they are forced back across the mitochondrial membrane as protons accumulate. One ATP, ready to be used for energy, is formed for every pair of hydrogen ions crossing the cell membrane.

How Does Metabolism Change during the Absorptive and Postabsorptive States? Available to be used by the body. The absorptive state is the period within four hours following a meal in which anabolic processes exceed catabolic processes and the body uses glucose as the primary source of energy. The postabsorptive state is the period usually more than four hours after eating in which the body uses glucose stored as glycogen and fatty acids and glycerol stored in triglycerides for fuel. Both states are regulated by hormones.

How Does Metabolism Change during the Absorptive and Postabsorptive States? During the absorptive state, metabolism favors energy storage. Metabolism adjusts to either provide energy for immediate use or store it for later. Carbohydrates are stored as glycogen. The liver and muscles can convert excess glucose to glycogen, but red blood cells and the central nervous system cannot. Only the liver can break down the glycogen and release it into the blood for red blood cells and the central nervous system to use when blood glucose levels are low. If glucose levels are high in the liver, glucose can be converted to glycogen through glycogenesis , or it can circulate to the other tissues. Enzymes in muscle can also convert excess glucose to glycogen. The body has a limited ability to store glycogen. Liver glycogen helps maintain glucose homeostasis. Glycogen in the liver can be converted to blood glucose through glycogenolysis in response to low blood glucose levels. Liver glycogen levels are nearly depleted 12 to 18 hours after eating. Muscle lacks the ability to release stored glucose into the blood; the stored glucose can be used for energy or stored as glycogen but cannot be used to maintain blood glucose levels.

How Does Metabolism Change during the Absorptive and Postabsorptive States? Excess carbohydrates and amino acids are stored as triglycerides. After glycogen stores are full and energy needs are met, carbohydrates will be converted to triglycerides. After protein has been used for all of its needed functions in the body, the excess is converted to body fatty acids. Fatty acids are stored as triglycerides. Lipogenesis , an anabolic pathway that synthesizes fatty acids to be stored, is the process through which any excess kilocalories will be stored as triglycerides. Lipogenesis is a separate and distinct path from fat breakdown; one pathway is not the mere reversal of the other. Lipogenesis occurs in the cytosol, not the mitochondria, and different endocrine hormones influence each pathway. The acetyl CoA molecule eventually becomes a long-chain fatty acid that attaches to a glycerol backbone and is stored as a triglyceride in fat cells.

How Does Metabolism Change during the Absorptive and Postabsorptive States? During the postabsorptive state, metabolism favors energy production. Glycogen stores supply energy during short periods of fasting, but after more than 18 hours without carbohydrates, the body adapts differently. At first, blood glucose levels are maintained through use of liver glycogen ( glycogenolysis ). Lipolysis provides fatty acids for energy, reducing the use of glucose by the cell. After liver glycogen has been depleted, gluconeogenesis is initiated using amino acids, glycerol, pyruvate, and lactate. Ketone bodies , derived from fatty acids, are used if fasting continues.

How Does Metabolism Change during the Absorptive and Postabsorptive States? Stores are depleted during fasting. If an individual has fasted or had limited carbohydrate intake for three days, ketogenesis (the formation of ketone bodies) reaches peak levels. Acetyl CoA is in great supply because it is not being metabolized in the TCA cycle due to a shortage of oxaloacetate. The brain uses ketone bodies for fuel when stores are low to reduce the consumption of blood glucose. Ketogenesis generates energy during prolonged fasting. If ketogenesis progresses to ketoacidosis , or if it occurs among diabetics, the consequences can be harsh (impaired heart action, coma, and death).

How Does the Body Metabolize Alcohol? Alcohol contains kcals without the presence of nutrients, but it can be a significant source of energy. Alcohol is also distinct from the other macronutrients because it doesn’t have to be digested before it is absorbed. After alcohol is absorbed, it is gradually metabolized by the enzymes in the liver. A small amount of alcohol can be quickly metabolized, but excess amounts will circulate in the body until the liver enzymes can break the alcohol down. Alcohol is metabolized through three distinct pathways: oxidation of ethanol by the enzyme alcohol dehydrogenase (ADH), the microsomal ethanol oxidizing system (MEOS) , and the metabolism of alcohol to form acetaldehyde hydrogenase within the human brain. Excess alcohol is stored as fat. If this continues for an extended period of time, a fatty, diseased liver can develop and lead to cirrhosis

What Are Genetic Disorders of Metabolism? Of the 1,000 genes that have been identified as causing disease in humans, more than 95 percent of them are from a single, dysfunctional gene referred to as monogenic. The lack of an appropriate enzyme prevents one substrate from being converted to another, causing a buildup of by-products that can be toxic. Phenylketonuria (PKU) is a rare monogenic disorder that results from the inability to metabolize the essential amino acid phenylalanine. Under these conditions, phenylalanine accumulates in the blood, a condition called hyperphenylalanemia . People with PKU must avoid high-protein foods and eliminate any products containing aspartame. Maple syrup urine disease (MSUD) results from mutations of four genes that provide instructions for making proteins from the amino acids leucine, isoleucine, and valine. Treatment includes avoiding foods such as beef, chicken, fish, eggs, nuts, and legumes; such a restrictive diet leaves room for little else save for medically produced formulas.

What Are Genetic Disorders of Metabolism? Homocystinuria is an inherited monogenic disorder in which the body cannot convert homocysteine to cystathionine. Treatment includes a diet low in the amino acid methionine, along with supplemental amounts of B vitamins. Galactosemia is a disorder that results in the inability to convert galactose to glucose; the result is a buildup of galactose in the blood. The treatment focuses on restricting dietary lactose and galactose, which means avoiding milk and all dairy products, and products that contain milk chocolate, whey protein or whey solids, casein, and dry milk solids. Glycogen storage disease is a genetic disorder that disrupts glycogenolysis in the liver. If glycogen is trapped in the liver, the body is unable to maintain normal blood glucose levels between meals. Treatment includes restriction of foods that contain sucrose, lactose, galactose, and fructose because these carbohydrates are often stored as glycogen in the liver.

What Is Energy Balance and Why Is It Important? Body weight and body composition are influenced by energy balance . Energy balance: energy in = energy out. Energy imbalance results in weight gained or lost. Positive energy balance (gaining weight) results in an increase in muscle mass, fat mass, or both. Positive energy balance is essential during certain times, such as pregnancy or adolescence, strength training, and when the body is recovering from injury. When a healthy adult exists in positive energy balance, weight gain will occur, most likely existing as fat in adipose tissue. There are 3,500 excess kcals in one pound of stored body weight; this is a basic kcal number and useful to explain the concept of excess food energy.

What Is Energy Balance and Why Is It Important? A ne gative energy balance (losing weight) occurs if food intake is reduced, exercise is increased, or both. Weight loss comes from a loss of body fat, muscle mass, glycogen reserves, or water weight. As less energy is consumed, more of the energy needs of the body are met by metabolizing energy reserves, such as stored fat. Negative energy balance usually results in weight loss predominantly from adipose tissue. Food and beverages provide energy in. One way to calculate kcal content is in the lab using a bomb calorimeter . This instrument measures heat and chemicals released by combustion, thus tracking the energy released by kcals present in food. Because some differences exist in how a body processes food and how a bomb calorimeter measures energy (the body is not as efficient and doesn’t completely metabolize or ingest food consumed), some adaptation of results is necessary. Physiological fuel values , corrected values to reflect kcals actually transformed to energy in the body, are the caloric values presented in food composition tables.

What Is Energy Balance and Why Is It Important? Those without a lab containing a bomb calorimeter can estimate kcals by multiplying the grams of carbohydrates, protein, fat, and alcohol in the food by the kilocalories contained in each gram. This is often done with the aid of analysis software or food composition tables. Body processes and physical activity result in energy out. Energy expenditure is different for every individual. It depends on basal metabolism, the thermic effect of food, the thermic effect of exercise, and adaptive thermogenesis.

How Is Total Daily Energy Expenditure Calculated? Staying at a stable weight, or trying to gain or lose weight, can be made easier through knowledge of total daily energy expenditure (TDEE) , which varies by individual. Basal and resting metabolic rate contribute to TDEE. Basal metabolism, or the energy needed to fuel the body’s vital functions while at rest (but not asleep), is expressed as a basal metabolic rate (BMR) . Approximately 60 percent of our daily energy needs are determined by our BMR. Multiple factors influence BMR , including lean body mass , or LBM (about 70 percent of BMR), age, gender, body size, genes, ethnicity, stress, thyroid hormone, nutritional state, environmental temperature, and caffeine and nicotine intake.

How Is Total Daily Energy Expenditure Calculated? BMR should be measured when cellular activity is at the lowest, such as in the morning in a comfortable environment after a 12-hour fast. Because it can be difficult to properly obtain BMR, resting metabolic rate (RMR) is often used. RMR is measured when a person is lying still in a comfortable environment after a three- or four-hour fast. RMR is likely to be about 6 percent higher than BMR. Heat produced by muscle contraction, tracked as the thermic effect of exercise (TEE) , can significantly contribute to daily energy expenditure. Factors influencing TEE include the type of activity performed, the time the activity is performed, and body weight. A heavier person will burn more kcals during equivalent physical activity. The amount of energy expended by sedentary people is less than half of their BMR. Physically active people with greater muscle mass can have a TEE twice their BMR. The more physical activity we perform each day, the more kcals we require to meet our energy needs. Furthermore, exercise enhances muscle mass and increases the need for kcals for a short period of time after the exercise has stopped.

How Is Total Daily Energy Expenditure Calculated? There is also a small amount of energy expended as non-exercise activity thermogenesis (NEAT). This form of energy expenditure is due to the activities of daily living, such as playing, fidgeting, various body motions, and the energy to maintain body posture. Energy used for digestion and absorption is called the thermic effect of food (TEF). About 10 percent of the kcals from food is used for digesting, absorbing, transporting, metabolizing, and storing energy-yielding nutrients. Protein has the greatest thermic effect, carbohydrate is in the middle range, and fat has the lowest or least thermic effect. The kcals used for TEF represent a small amount compared to the amount of energy expended by BMR and physical activity Energy is used for adaptive thermogenesis. Adaptive thermogenesis is the body’s regulation of heat production. It is influenced by changes in temperature, diet, and stress, which result in a changes in metabolism. The direct connection between adaptive thermogenesis and total daily energy expenditure is uncertain.

How Do We Measure Energy Expenditure? Several methods are available to measure energy expenditure. Some of the methods are expensive and require a trained person; other methods are very straightforward. Direct and indirect calorimetry measure energy expenditure. Direct calorimetry measures the amount of heat the body generates and can be determined using a metabolic chamber. This is a sophisticated, precise method for determining the energy expended by the body, but can be expensive and impractical for most people. Indirect calorimetry estimates the amount of energy expended by the body by measuring the amount of oxygen consumed versus the amount of carbon dioxide produced during exercise.

How Do We Measure Energy Expenditure? Some basic calculations exist that estimate energy expenditure based on a person’s gender, age, height, weight, and physical activity. (These equations are illustrated in the Calculation Corner in this section.) The estimated energy requirement (EER) is the average estimated kcal intake needed to maintain energy balance; it can be precisely tracked by assessing every single physical activity done during the day. The Harris-Benedict equation is a well-known formula that uses resting metabolic rate and can be an acceptable alternative to the EER. Those who are very muscular or very fat will not likely find an accurate measurement, as the formula does not account for lean body mass.

What Is Body Composition and How Is It Assessed? Body composition is the ratio of fat tissue to lean body mass. It is measured or stated as a percent of body fat. Primarily, measuring the health risks of too much body fat is the concern. Most body fat is stored in adipose tissue. Total body fat is made up of essential fat (in the bone marrow, heart, lungs, liver, spleen, kidneys, intestines, muscles, and central nervous system) and stored fat (found in adipose tissue or fat cells). Essential fat is needed for the body to function. Women have more essential fat then men—about four times more—due to fat related to pregnancy and lactation. Every cell contains some fat, but most body fat is found in adipose tissue as storage fat, either under the skin as subcutaneous fat or around the internal organs as visceral fat Both subcutaneous and visceral fat protect and cushion internal organs and insulate the body from cold temperatures. Women are more likely to accumulate subcutaneous fat in the breasts, neck, upper arms, hips, and thighs, as opposed to men who are more likely to store it in the belly, hips, and thighs.

What Is Body Composition and How Is It Assessed? Adipose tissue expands and shrinks based on the kcal input and kcal output of the human body. Most adipose tissue is referred to as white fat because of its white color, but brown adipose tissue (BAT) also exists BAT is made up of specialized cells that contains more mitochondria and a richer blood supply compared to white fat. The purpose of white fat is to store kcals and the purpose of brown fat is to generate body heat. Infants have the largest supply of brown fat; some adults retain brown fat, but most adults have minimal to no brown fat reserves. Energy is wasted by brown fat, as kcals are converted into heat rather than being stored by the body.

What Is Body Composition and How Is It Assessed? Body fat distribution affects health. Central or android obesity is excess fat stored in the abdomen or center of the body. Gynoid obesity is fat that is stored lower on the body. Visceral fat is believed to create a greater fatty acid release from the liver. It may lead to insulin resistance, high levels of blood fat, low levels of HDL cholesterol, and elevated LDL cholesterol. Men, postmenopausal women, and obese people tend to struggle with excess visceral fat

What Is Body Composition and How Is It Assessed? Body composition is assessed indirectly. The various methods of assessing body composition yield reliable results and are used depending on convenience and need of particular results. Hydrostatic weighing and air displacement plethysmography rely on body volume to measure body fat percentage. Hydrostatic weighing compares the body weight in air compared to body weight under water. The BodPod uses the same principle in relation to air displacement rather than water displacement. The Calculation Corner shows the equations used to determine body composition from either of these body volume methods.

What Is Body Composition and How Is It Assessed? Dual energy X-ray absorptiometry (DEXA) is considered the most accurate method of determining body composition. Two X-ray beams are used to evaluate tissues and lean body mass; a computer calculates the difference to determine body fat percentage. Bioelectrical impedance analysis (BIA) measures the resistance to a low-energy current that travels through muscle and body fat. Since the rate of the resistance is different between fat and muscle, the information (current flow) can be used to determine body fat percentage. This method is not as reliable as others and can be affected by age, hydration status, and consumption of food and alcohol prior to the test. Anthropometric techniques are the simplest to use and only involve a skinfold caliper to measure fat at various body locations. A trained technician pinches the fat fold and takes the measurement in millimeters; these values are then used to calculate body fat percentage. A simple measurement of waist circumference can reveal the risk for increased visceral fat.A woman with a waist measurement that is less than 35 inches and a man with a number less than 40 inches are at lower risk than those with larger measurements. A person with a healthy BMI can be at higher health risk if excess fat is around the middle.

How Do We Estimate a Healthy Body Weight? Body weight and body composition are not synonymous, but the terms are often used interchangeably. Body weight is the total mass of a person expressed as either pounds or kilograms. Body composition is the percentage of body weight that is composed of fat and lean body mass. Height and weight tables can provide a healthy weight range. There are disadvantages to relying on these measurements for medical decisions. The information on these charts is generally based on men’s and women’s measurements between the ages of 25 and 59 years of age, so older and younger individuals are underrepresented. The original data was not standardized by researchers—much of the data was self-reported, and no instructions regarding wearing clothing and shoes during measurements were consistently given. The tables were constructed under the assumption that weight is associated with body fat. Due to some unreliability in standards for medical decisions, these tables are primarily used by insurance companies for mortality rates.

How Do We Estimate a Healthy Body Weight? Body mass index (BMI) is a useful indicator of healthy weight for most people. One of two formulas can be used to calculate BMI. As BMI rate increases above 25, the risk of dying from disease increases. A BMI of 18.5 to 24.9 is considered a healthy weight . A BMI between 25 and 29.9 is overweight . A BMI above 30 is considered obese . Obese individuals are 50 to 100 percent more likely to die prematurely than those at a healthy weight.

How Do We Estimate a Healthy Body Weight? There are health risks associated with body weight and body composition. Because of its relation to body composition, body weight can be a predictor of health. Heavier people who typically have a higher percentage of body fat tend to face greater health risks. Being underweight increases health risks. Some people are naturally slender, but underweight (a BMI of less than 18.5) can be a result of malnutrition, substance abuse, or disease. Those who are underweight can be at higher risk of anemia, osteoporosis, bone fractures, heart irregularities, amenorrhea, depression, anxiety, inability to fight off infection, trouble with body temperature regulation, decreased muscle strength, and even premature death. Certain diseases (cancer, inflammatory bowel disease, celiac disease) may cause underweight as a result of chronic malabsorption. Other causes of underweight include side effects from various medicines that decrease the appetite, smoking, and substance abuse. Being overweight increases health risks. The main diseases and conditions associated with being too heavy are heart disease, hypertension, stroke risk, high blood lipids, diabetes, metabolic syndrome, and several cancers. A BMI greater than 40 or more than 100 pounds over ideal body weight is considered severe obesity .

What Is Disordered Eating? The term disordered eating is used to describe a variety of eating patterns considered abnormal and potentially harmful. Eating disorders , in contrast, are diagnosed when a person meets specific criteria that include disordered eating patterns as well as other conditions. One can exhibit disordered eating behavior without having an actual eating disorder. Approximately 20 million women and 10 million men in the U.S. struggle with various eating disorders; anyone can develop an eating disorder, regardless of gender, age, race, ethnicity, or social status. Anorexia nervosa results from severe kilocalorie restriction. Sufferers have an intense fear of gaining weight or being “fat.” A distorted body image causes them to see obesity even though they are usually underweight. Health consequences of anorexia include electrolyte imbalances, irregular heart rhythm, and low blood potassium (the most fatal effect). Sufferers feel cold despite the temperature due to lack of body fat, and actually grow down-like body hairs ( lanugo ) especially on the face and arms.

What Is Disordered Eating? Bulimia nervosa involves cycles of binge eating and purging. The binge-eating part of the cycle usually lasts a short time; the purging can take on several forms: vomiting, vigorous exercise, diet pills, laxatives, diuretics, or extreme fasting. Binge eating disorder involves compulsive overeating; there is no purge cycle to this disorder. Other disordered eating behaviors can be harmful. Orthorexia is a disorder in which the person fixates on what he or she believes to the “right” foods to consume. Gradually, the sufferer finds reasons to remove more groups of nutrition from the consumption list and can easily slip into anorexia nervosa. Night eating syndrome involves consumption of a majority of daily calories between 8:00 p.m. and 6:00 a.m. The sufferer will often wake up in the middle of the night to eat. These individuals claim to have little appetite during normal eating times. Pica refers to a strong compulsion to eat, lick, or chew nonnutritive substances such as clay, dirt, or chalk for a period of at least 1 month.

What Is Disordered Eating? Different eating disorders have some traits and signs in common. People with eating disorders are commonly perfectionists; they may be attempting to gain some control in their lives, and they are prone to depression and low self-esteem. Eating disordered can be treated. The most effective treatment is a multidisciplinary approach that includes psychological, medical, and nutrition professionals.

Critical Thinking What are the financial consequences of obesity and health insurance costs (premiums, expenses related to obesity)? Should thin, healthy people pay reduced health insurance premiums? Should heavy, ill people pay increased health insurance premiums?

Critical Thinking What it would be like to shop for clothes at this weight, try to sit comfortably in an airplane or a movie theatre, go to the doctor and be weighed, mingle socially at a class reunion, and attend a mixer for a professional group. Do you think you would face job discrimination? Pity? Teasing? Discuss what happens to people in our society who exceed 400 pounds.