25.1 Digestive System

• One of the basic characteristics of life is the ability to acquire nutrients for energy to conduct activities of living.

• In animals, the digestive system consists of organs involved in four processes:

  • Ingesting food

  • Breaking down food into smaller molecules that can be transported

  • Absorbing nutrient molecules

  • Eliminating indigestible materials

• The digestive system maintains homeostasis by providing the body's cells with the nutrients they need to continue functioning.

• The digestive system interacts with other organ systems of the body to maintain homeostasis.

Complete and Incomplete Digestive Systems

• Hydras and planarians have an incomplete digestive system with a single opening serving as both entrance and exit.

• Most animals, like earthworms, have a complete digestive tract with a tube-within-a-tube configuration.

• The inner tube, or the digestive tract, has both an entrance (the mouth) and an exit (the anus).

• The inner tube is separated from the outer tube (the body wall) by the coelom.

• Specialized organs that assist with digestion are located within the coelom.

• Digestion of food is an extracellular process in all animals, including earthworms and humans.

• Digestive enzymes are produced by glands in the wall of the digestive tract or by accessory glands that lie nearby and are released into the tract.

• Food is never found within these accessory glands, only within the digestive tract itself.

The Digestive Tract

• The digestive tract of humans, and most other vertebrates, consists of the mouth, esophagus, stomach, small intestine, and large intestine.

Mouth

• The digestive system in humans begins with the mouth, where food is chewed into pieces, starting the process of mechanical digestion.

• Many vertebrates have teeth, but birds lack teeth and use small pebbles in their gizzard to break up food.

• Mammals' teeth reflect their diet, with carnivores having easily digestible meat and herbivores needing to break down cellulose walls in plant material.

• Humans are omnivores with sharp incisors for biting, pointed canines for tearing, and premolars and molars for grinding and crushing food.

• Digestive enzymes break down large molecules in food to smaller molecules.

• Salivary glands in the mouth produce saliva, including salivary amylase which breaks down starch to maltose.

• The tongue manipulates food and mixes it with saliva to form a bolus, which is then swallowed.

Swallowing

• The human digestive and respiratory passages meet in the pharynx and then separate.

• When food is swallowed, the soft palate moves up to close off the nasal cavities.

• The epiglottis covers the glottis to prevent food from entering the larynx.

• The bolus must move through the pharynx and into the esophagus because the air passages are blocked.

• Food can sometimes go the wrong way, either into the nasal cavities or into the trachea.

• The esophagus is a muscular tube that takes food to the stomach.

• Peristalsis, a series of rhythmic contractions of smooth muscles, moves the contents along in tubular organs, including the esophagus.

Stomach

• The human stomach:

  • Thick-walled, J-shaped organ on the left side of the abdominal cavity below the liver.

  • Continuous with the esophagus above and the duodenum of the small intestine below.

  • The cardiac sphincter separates the esophagus from the stomach.

  • About 25 cm (10 in.) long, regardless of the amount of food it holds.

  • The diameter varies depending on how full it is.

  • Receives food from the esophagus, stores food, starts the digestion of proteins, and moves food into the small intestine.

  • Wall has deep folds which disappear as the stomach fills to an approximate capacity of 1 liter.

  • Contains three muscle layers: longitudinal, circular, and obliquely arranged.

  • Mechanically digests food by contracting vigorously to mix it with digestive juices.

  • The epithelial lining of the stomach called a mucosa, has millions of gastric glands.

  • Gastric glands produce gastric juice containing hydrochloric acid and pepsin.

  • Strong acidity kills microbes and promotes the activity of pepsin.

  • Low pH sometimes causes heartburn or gastric reflux disease.

  • A thick layer of mucus protects the wall of the stomach from enzymatic action.

  • Ulcers are open sores in the wall caused by the gradual destruction of tissues.

  • Alcohol and other liquids are absorbed in the stomach, but other nutrients are not.

  • Peristalsis pushes food along in the stomach.

  • The pyloric sphincter is a narrow opening at the base of the stomach.

  • Chyme is a thick, soupy liquid that leaves the stomach and squirts through the pyloric sphincter into the small intestine.

• Ruminants:

  • A type of mammal that includes cattle, sheep, goats, deer, and buffalo.

  • Named for a part of their stomach, the rumen.

  • Rumen contains symbiotic bacteria and protozoans that produce enzymes that can digest cellulose.

  • Herbivores feed on grass, which goes to the rumen and is broken down by the microbes, becoming small balls of cud.

  • Cud returns to the mouth, where the animal "chews the cud."

  • Cud may return to the rumen for a second go-round before passing through the other chambers of the stomach.

  • Rumen is an adaptation to a diet rich in fiber that may have been promoted by competition among the many types of animals that feed on grass.

Small Intestine

• Food is chewed in the mouth and mixed with salivary amylase, which digests starch to maltose.

• In the stomach, pepsin digests proteins to peptides, and the contents of the digestive tract become chyme.

• Chyme passes to the small intestine, where it is digested and absorbed.

• The duodenum, the first part of the small intestine, receives secretions from the pancreas and liver.

• The liver produces bile, which breaks up fat droplets by emulsification.

• The pancreas produces pancreatic juice, which contains sodium bicarbonate and digestive enzymes.

• The small intestine contains villi, which produce intestinal enzymes that complete the digestion of peptides and sugars.

• Nutrient molecules are absorbed into cells throughout the body from the bloodstream.

• Absorption by Villi:

  • The small intestine wall has an extensive surface area for absorbing nutrient molecules.

  • Circular folds on the mucous membrane layer of the small intestine give it a corrugated appearance.

  • Villi are present on the surface of these circular folds.

  • Cells on the surface of the villi have microvilli.

  • Villi absorb small nutrient molecules into the body.

  • Each villus contains a network of blood capillaries and a lymphatic capillary called a lacteal.

  • Sugars and amino acids enter the blood capillaries of a villus and are carried to the liver by the hepatic portal system.

  • Glycerol and fatty acids enter the epithelial cells of the villi and are packaged as lipoprotein droplets, which enter a lacteal.

  • Absorption occurs by diffusion and active transport.

  • Lymphatic vessels transport lymph to cardiovascular veins.

  • The bloodstream carries the nutrients absorbed by the digestive system to all the cells of the body.

Large Intestine

• The word bowel refers to the digestive tract between the stomach and the anus, but it is sometimes used to refer only to the large intestine.

• The large intestine (colon) absorbs water, salts, and some vitamins, and stores indigestible material until it is eliminated at the anus.

• The large intestine has a blind pouch called the cecum, with a small projection containing lymphatic tissue called the appendix.

• The appendix may play a role in fighting infections by acting as a reservoir of beneficial bacteria, but if it becomes infected and bursts, it can cause peritonitis.

• The large intestine has a large population of bacteria, including Escherichia coli, which break down indigestible material and produce vitamin K.

• Feces are about 75% water and 25% solid matter, with almost one-third of the solid matter made up of intestinal bacteria.

• A diet that includes fiber adds bulk to the feces, improves elimination regularity, and prevents constipation.

• About 1.5 liters of water enter the digestive tract daily from eating and drinking, and an additional 8.5 liters enter carrying various substances secreted by digestive glands.

• 95% of this water is absorbed by the small intestine, and much of the remaining portion is absorbed by the large intestine.

• The large intestine is more subject to the development of polyps, which can be removed surgically.

• Figure 25.11 reviews the process of digestion and the roles of the digestive organs.

Accessory Organs

• The pancreas and liver are the main accessory organs of digestion, along with the salivary glands and gallbladder. Here are some bullet points to clarify and summarize their functions:

• Pancreas:

  • Functions as both an endocrine and exocrine gland

  • Produces and secretes insulin and glucagon into the bloodstream as an endocrine gland

  • Produces and secretes pancreatic juice into the duodenum of the small intestine through the common bile duct as an exocrine gland

• Liver:

  • Detoxifies the blood by removing and metabolizing poisonous substances

  • Produces plasma proteins, destroys old red blood cells, and converts hemoglobin to the breakdown products in bile

  • Produces bile, which emulsifies fats in the small intestine

  • Stores glucose as glycogen and breaks down glycogen to glucose between meals to maintain a constant glucose concentration in the blood

  • Produces urea from amino acids and ammonia

  • Helps maintain the glucose concentration in blood at about 0.1% by removing excess glucose from the hepatic portal vein and storing it as glycogen

  • Converts amino acids to glucose molecules by removing amino groups from the amino acids through deamination

  • Can develop disorders such as jaundice, hemolytic jaundice, obstructive jaundice, hepatitis, and cirrhosis

Digestive Enzymes

• Smelling food and thinking about food can cause the nervous system to order the secretion of digestive juices.

• Digestive juices are influenced by several peptide hormones.

• Eating a protein-rich meal causes the stomach wall to produce a peptide hormone that enters the bloodstream and causes the stomach to produce more gastric juices.

• The presence of protein and fat in the small intestine stimulates the secretion of bile and pancreatic juices through another peptide hormone made in the intestinal wall.

• Digestive enzymes present in the digestive juices help break down carbohydrates, proteins, nucleic acids, and fats.

• Starch digestion begins in the mouth with saliva from the salivary glands containing salivary amylase, the first enzyme to act on starch.

• Maltose is a disaccharide that cannot be absorbed by the intestine.

• Additional digestive action in the small intestine converts maltose to glucose.

• Glucose can be absorbed by the intestine.

• Protein digestion begins in the stomach.

• Gastric juice secreted by gastric glands has a very low pH of about 2.

• Gastric juice contains hydrochloric acid (HCl).

• Pepsin is present in gastric juice.

• Pepsin acts on a protein molecule to produce peptides.

• Peptides are usually too large to be absorbed by the intestinal lining.

• Peptides are broken down to amino acids in the small intestine.

• Starch, proteins, fats, and nucleic acids are enzymatically broken down in the small intestine.

• Pancreatic juice enters the duodenum and has a basic pH due to the presence of sodium bicarbonate (NaHCO3).

• Pancreatic amylase is a pancreatic enzyme that digests starch.

• Maltose, a disaccharide, cannot be absorbed by the intestine.

• Additional digestive action in the small intestine converts maltose to glucose, which can be absorbed.

• Protein digestion begins in the stomach.

• Gastric juice secreted by gastric glands has a very low pH—about 2—because it contains hydrochloric acid (HCl).

• Pepsin, which is also present in gastric juice, acts on a protein molecule to produce peptides.

• Maltase and peptidases are enzymes produced by the small intestine.

• Maltase completes the digestion of maltose to glucose.

• Peptidases complete the digestion of proteins into amino acids.

• Glucose and amino acids are small molecules that are absorbed into the cells of the villi and enter the blood.

• Other disaccharides have specific enzymes for digestion in the small intestine.

• The lack of any of these enzymes can lead to illness.

• Peptides, formed during the initial stage of protein digestion, are broken down into amino acids by peptidases.

• Lipase, a third pancreatic enzyme, digests fat molecules in fat droplets that have been emulsified by bile salts.

• The end products of lipase digestion are monoglycerides and fatty acids.

• Monoglycerides consist of glycerol and one fatty acid.

• Monoglycerides and fatty acids enter the cells of the villi.

• In the cells of the villi, monoglycerides and fatty acids are rejoined and packaged as lipoprotein droplets.

• Lipoprotein droplets are called chylomicrons.

• Chylomicrons enter the lacteals.

25.2 Nutrition

• Proper nutrition is essential for the functioning of the body's immune system, muscles, bones, and blood circulation.

• Nutrients are substances in food that perform physiological functions in the body, provide energy, promote growth and development, and regulate cellular metabolism.

• Nutrients help maintain fluid balance, proper pH of blood, and are involved in homeostasis.

• A nutrient deficiency can lead to signs and symptoms of a deficiency disorder.

• Vitamin C is needed to synthesize and maintain collagen, and its deficiency can cause gums to bleed and skin to bruise easily.

• Learning about nutrition can improve diet and increase the likelihood of a longer, more active, and productive life.

• Poor diet and lack of physical activity are responsible for seven of the leading ten causes of death in the United States annually.

• Learning what constitutes a poor diet versus a healthy diet can help choose foods that supply all the nutrients in proper balance.

Introducing the Nutrients

• A person's diet refers to their typical food choices.

• Cultural and ethnic backgrounds, financial situations, environmental conditions, and psychological states influence what we eat.

• A balanced diet provides all the necessary nutrients in proper proportions for a healthy body.

• There are six classes of nutrients: carbohydrates, lipids, proteins, minerals, vitamins, and water.

• Essential nutrients must be supplied by the diet because the body cannot produce them in sufficient quantity.

• Macronutrients (carbohydrates, lipids, and proteins) are needed in large quantities, while micronutrients (vitamins and minerals) are needed in small quantities.

• Macronutrients, not micronutrients, supply our energy needs.

• Foods with high water content are usually lower in energy content than foods with less water and more macronutrient content.

• No single naturally occurring food contains enough essential nutrients to meet all of our nutrient needs.

• "Bad" or "junk" foods have nutritional value but are more appropriately called empty-calorie foods because they have high amounts of fat and/or sugar in relation to their vitamin and mineral content.

• Diets that contain too many empty-calorie foods will lack enough vitamins and minerals.

25.3 The Classes of Nutrients

• The human diet must contain macronutrients and micronutrients in the correct proportions.

• Macronutrients are energy nutrients.

• Each type of nutrient has more than one function in the body.

• Nutrients can be supplied by several different food sources (refer to Table 25.1.)

Carbohydrates

• Carbohydrates are present in food as sugars, starch, and fiber.

• Fruits, vegetables, milk, and honey are natural sources of sugars.

• Glucose and fructose are monosaccharide sugars, while lactose (milk sugar) and sucrose (table sugar) are disaccharides.

• All sugars are converted to glucose for transport in the blood after absorption into the body.

• Glucose is the preferred direct energy source in cells.

• Plants store glucose as starch, and animals store glucose as glycogen.

• High-starch foods are beans, peas, cereal grains, and potatoes.

• Starch is digested to glucose in the digestive tract, and any excess glucose is stored as glycogen.

• Animal sources of food, except for honey and milk, do not contain carbohydrates.

Fiber

• Fiber is a type of nondigestible carbohydrate derived from plants.

• Foods rich in fiber include beans, peas, nuts, fruits, and vegetables.

• Whole-grain products are a good source of fiber and are more nutritious than food products made from refined grains.

• During the refinement of grains, fiber, vitamins, and minerals are removed, leaving primarily starch.

• Fiber cannot be digested to small molecules that enter the bloodstream, so it is not a nutrient for humans.

• Insoluble fiber adds bulk to fecal material, preventing constipation.

• Soluble fiber combines with bile acids and cholesterol in the small intestine and prevents them from being absorbed, protecting against heart disease.

• The recommended daily intake of fiber is 25 g for women and 38 g for men.

• To increase fiber intake, eat whole-grain foods, fresh fruits, and raw vegetables, and include nuts and beans in your diet.

Can Carbohydrates Be Harmful?

• Following Atkins or Paleo diet may lead to the belief that carbs are unhealthy and should be avoided.

• Nutritionists suggest that carbohydrates should supply a large portion of energy needs.

• Americans are not eating the right kind of carbohydrates.

• Traditional diets in some countries consist of 60-70% high-fiber carbohydrates and have a low incidence of diseases.

• Obesity is associated with type 2 diabetes and cardiovascular disease.

• High intake of refined carbohydrates and fructose sweeteners may be responsible for obesity in the US

• Table 25.2 provides ways to reduce dietary sugars in the diet.

• Consuming too much energy from any source contributes to body fat and increases the risk of obesity and associated illnesses.

• It is difficult to determine which dietary component is responsible for the current epidemic of obesity among Americans.

• There is no scientific basis for the belief that children become hyperactive after eating sugar.

• Sucrose is broken down into glucose and fructose in the small intestine and absorbed into the bloodstream.

• Excess glucose and fructose enters the liver, and fructose is converted to glucose.

• The liver stores glucose as glycogen and breaks it down to maintain proper glucose levels.

Lipids

• Triglycerides supply energy for cells like carbohydrates, but fat is stored for the long term in the body.

• Subcutaneous fat deposits under the skin insulate the body from cold temperatures.

• Deeper fat deposits in the trunk protect organs against injury.

• Nutritionists recommend unsaturated fats over saturated fats in the diet.

• Alpha-linolenic and linoleic acids are essential dietary fatty acids that can be found in fatty fish and plant oils.

• Delayed growth and skin problems can develop when the diet lacks essential fatty acids.

• Animal foods contain saturated fats, while plant oils contain unsaturated fats.

• Cholesterol is synthesized by the body and is used to make various compounds, including bile, steroid hormones, and vitamin D.

• Cholesterol is an important component of the plasma membrane.

• Only animal foods are rich in cholesterol, while plant foods do not contain cholesterol.

Can Lipids Be Harmful?

• Elevated blood cholesterol levels increase the risk of cardiovascular disease, which is the leading cause of death in the US.

• A diet high in cholesterol and saturated fats also increases the risk of cardiovascular disease.

• Trans fats are even more harmful than saturated fats, and are formed when unsaturated oils are hydrogenated to produce solid fats.

• Trans fatty acids can reduce the function of plasma membrane receptors that clear cholesterol from the bloodstream.

• Trans fats are commonly found in processed foods, commercially fried foods, packaged snacks, vegetable shortening, and some margarine.

• Table 25.3 provides information on how to reduce harmful lipids in the diet.

Proteins

• Dietary proteins are broken down into amino acids.

• Cells use amino acids to synthesize hundreds of cellular proteins.

• 9 out of the 20 different amino acids are essential and must be present in the diet.

• Lack of essential amino acids in children's diets can result in stunted growth.

• Animal-derived foods such as eggs, milk products, meat, and poultry contain all 9 essential amino acids and are considered "complete" or "high-quality" protein sources.

• Plant-derived foods generally have less protein per serving and lack one or more essential amino acids, making them "incomplete" or "low-quality" protein sources.

• Vegetarians can meet their protein needs by consuming grains, beans, nuts, tofu, soymilk, and other foods made from processed soybeans in various combinations.

• A balanced vegetarian diet is possible with proper planning.

Can Proteins Be Harmful?

• Proteins should not supply the bulk of dietary calories, according to nutritionists.

• The average American eats twice as much protein as needed.

• Some diets encourage protein intake instead of carbohydrates as an energy source.

• Athletes may include amino acid or protein supplements in their diet to increase muscle mass.

• Excess amino acids are not always converted into muscle tissue and can be used as an energy source.

• The liver removes the nitrogen portion of amino acids and uses it to form urea, which is excreted in urine.

• High protein diets can cause dehydration due to the water needed for the excretion of urea.

• High protein diets can increase calcium loss in urine and encourage the formation of kidney stones.

• Many high-protein foods contain a high amount of fat.

Minerals

• The body needs 20 minerals for various physiological functions.

• Major minerals are needed in higher levels than trace minerals.

• More than 100mg/day of each major mineral is required in the diet.

• Less than 100mg/day of each trace mineral is required in the diet.

• Table 25.4 lists major and trace minerals, their functions, food sources, and health effects of too little or too much intake.

• Some individuals, especially women, may not get enough iron, calcium, magnesium, or zinc in their diets.

• Anemia results from a lack of iron in the diet.

• Calcium supplements are taken to counteract osteoporosis.

• Sodium intake should be limited to 2,300mg/day (1,500mg/day for those with high blood pressure.)

• The average American takes in over 4,000mg of sodium per day.

• The American Heart Association recommends limiting sodium intake to less than 1,500mg/day.

• Table 25.5 provides recommendations for reducing sodium in the diet.

Vitamins

• Vitamins are organic compounds that regulate metabolic activities.

• Vitamins are classified as water-soluble or fat-soluble.

• Water-soluble vitamins are readily removed in urine and must be replenished daily.

• Fat-soluble vitamins are stored in adipose tissue and persist longer in the body.

• Vitamins C, E, and A are antioxidants and defend the body against free radicals.

• It is suggested to eat about 4½ cups of fruits and vegetables per day to obtain these vitamins.

• Vitamin deficiencies can lead to disorders and even death.

• Some individuals are at risk for vitamin deficiencies due to poor food choices.

• Vitamin D deficiency leads to rickets, which causes bowing of the legs.

• Vitamin C deficiency can lead to scurvy.

• Alcohol consumption can interfere with vitamin absorption and increase excretion.

Water

• Water constitutes about 60% of an adult's body.

• Water participates in many chemical reactions.

• Watery fluids lubricate joints, transport other nutrients, and help maintain body temperature.

• Beverages, soups, fruits, and vegetables are sources of water.

• Most solid foods contain some water.

• The amount of total water (water from beverages and foods) that you need to consume depends on your physical activity level, your diet, and your environmental conditions.

• On average, men should consume about 125 ounces (oz), and women should consume about 90 oz of total water each day.

• Thirst is a healthy person's best guide for meeting water needs and avoiding dehydration.

• Too much water can also be a problem.

• In water toxication (hyponatremia), individuals who consume excessive amounts of water upset the balance of electrolytes, usually sodium and potassium, in their blood.

• This can lead to irregular heartbeat and, in some cases, death.

25.4 Understanding Nutrition Guidelines

• Planning nutritious meals and snacks involves making daily food choices based on a wide variety of information about recommended amounts of nutrients.

• A day’s food intake should provide the proper balance of nutrients—neither too much nor too little of each nutrient.

• Food guides can be helpful in planning your diet.

• Reading the “Nutrition Facts” panel on packaged foods can help you choose healthier sources of nutrients.

Updating Dietary Guidelines

• Dietary guidelines are revised every 5 years by the U.S. government.

• The latest guidelines were released in 2015 by the Departments of Agriculture and Health and Human Services.

• Overall purposes of guidelines are to promote health, prevent chronic long-term disease, and assist people in reaching and maintaining a healthy weight.

• New guidelines focus on establishing healthy eating patterns rather than prescribing quantitative levels for nutrients.

• Healthy eating pattern includes vegetables, fruits, grains, fat-free or low-fat dairy products, proteins, and oils.

• Specific recommendations were made to limit certain nutrients that raise health concerns, outlined in Table 25.8.

Visualizing Dietary Guidelines

• The USDA has developed a guideline called MyPlate.

• MyPlate is a graphical representation that replaced the older pyramids.

• MyPlate helps in deciding how daily calorie intake should be distributed among food choices.

• MyPlate emphasizes the proportions of each food group that should be consumed daily.

• The USDA provides recommendations on the ChooseMyPlate.gov website for the minimum quantity of foods in each group that should be eaten daily.

• The website also contains an interactive component, Super-Tracker, that allows tracking of personal diet and setting weight and activity goals.

• The USDA provides examples of daily food plans and information on how to follow a healthy diet on a budget to support these decisions.

Making Sense of Nutrition Labels

• A "Nutrition Facts" panel provides dietary information about the product and general information about the nutrients it contains.

• The serving size is based on the typical serving size for the product.

• The total number of Calories is based on the serving size.

• The % daily value is calculated by comparing the specific information about this product with the information given at the bottom of the panel.

• The % daily values are not applicable for people who require more or less than 2,000 Calories per day.

• A % daily value for protein is generally not given because determining such a value would require expensive testing of the protein quality of the product by the manufacturer.

• There is a % daily value for carbohydrates but not sugars, because there is no recommended daily value for sugar.

• "Nutrition Facts" panels can be used to compare two products of the same type if the serving sizes are the same.

Dietary Supplements

• Dietary supplements are nutrients and plant products used to enhance health.

• The U.S. government does not require dietary supplements to undergo safety and effectiveness testing like prescription drugs.

• Many herbal products have not been scientifically tested for benefits and can be poisonous.

• Dietary supplements containing nutrients can also cause harm, especially fat-soluble vitamins A and D.

• Excesses of water-soluble vitamins B6, thiamine, and C have been reported to cause toxicity.

• Minerals can be harmful or deadly when ingested in excess.

• Healthy people can take daily supplements with recommended amounts of vitamins and minerals.

• Some individuals with metabolic diseases or physical conditions may need to add certain nutrient supplements to their diet.

• High doses of dietary supplements should not be taken without consulting a physician.

The Bottom Line

• A healthy diet:

  • Has moderate total fat intake.

  • Is low in saturated fats, trans fats, and cholesterol.

  • Is rich in whole-grain products, vegetables, and legumes as sources of complex carbohydrates and fiber.

  • Is low in refined carbohydrates, such as starches and sugars.

  • Is low in salt and sodium content.

  • Contains adequate amounts of protein, largely from poultry, fish, and plants.

  • Includes only moderate amounts of alcohol.

  • Contains adequate amounts of minerals and vitamins.

  • Avoids questionable food additives and supplements.

25.5 Nutrition and Health

• Many serious disorders in Americans are linked to a diet that results in excess body fat.

• In the United States, the number of people who are overweight or obese has reached epidemic proportions.

• Nearly two-thirds of adult Americans have too much body fat.

• Excess body fat increases the risk of type 2 diabetes, cardiovascular disease, and certain cancers.

• These conditions are among the leading causes of disability and death in the United States.

• Therefore, it is important for us all to stay within the recommended weight for our height.

Body Mass Index

• Medical researchers use BMI to determine if a person is overweight or obese.

• Height is determined genetically, while weight is influenced by other factors such as diet and lifestyle.

• BMI reflects the relationship between a person's weight and height.

• To calculate BMI, use the following formula:

Energy Intake Versus Energy Output

• Genetics and physiological factors contribute to being overweight.

• A person becomes fat by taking in more food energy (calories) than are expended.

• Energy value of food is reported in kilocalories (kcal).

• A kilocalorie is the amount of heat that raises the temperature of a liter of water by 1°C.

• Food's caloric value can be estimated by knowing the grams of carbohydrate, fat, protein, and alcohol it contains.

• Each gram of carbohydrate or protein supplies 4 kcal, each gram of fat supplies 9 kcal, and each gram of alcohol supplies 7 kcal.

• A serving of food containing 30 g of carbohydrate, 9 g of fat, and 5 g of protein supplies 221 kcal.

• The body expends energy for:

  • Metabolic functions.

  • Physical activity.

  • Digestion, absorption, and processing of nutrients from food.

• Scientists can measure a person's energy expenditure for a specific physical activity by:

  • Measuring oxygen intake.

  • Measuring carbon dioxide output during the activity.

• Here are the steps to estimate your daily energy needs:

  • Kcal needed daily for metabolic functions:

    • Multiply your weight in kilograms (weight in pounds divided by 2.2) times 1.0 if you are a man, and times 0.9 if you are a woman. Then multiply that number by 24.

    • Example: Meghan, a woman who weighs 130 pounds (about 59 kg), would calculate her daily caloric need for metabolic functions as follows: 0.9 kcal × 59 kg × 24 hours = approximately 1,274 kcal/day.

  • Kcal needed daily for physical activity:

    • Choose a multiplication factor from one of the follow categories:

      • Sedentary (little or no physical activity) = 0.20 to 0.40

      • Light (walk daily) = 0.55 to 0.65

      • Moderate (daily vigorous exercise) = 0.70 to 0.75

      • Heavy (physical labor/endurance training) = 0.80 to 1.20

    • Multiply this factor times the kcal value you obtained in step 1.

    • Example: Meghan performs light physical activity daily. She multiplies 0.55 × 1,274 kcal to determine her daily caloric need for physical activity, which is 701 kcal.

  • Kcal needed for digestion, absorption, and processing of nutrients:

    • Multiply the total kcal from steps 1 and 2 by 0.1, and add that value to the total kcal from steps 1 and 2 to get your total daily energy needs.

    • Example: Meghan adds 1,274 and 701 and then multiplies 1,975 kcal by 0.1 and adds that value (197.5) to 1,975 to obtain her total daily energy needs of 2,172 kcal.

  • Therefore, to maintain her weight of 130 pounds, Meghan needs to consume about 2,170 kcal a day and perform light physical activities.

Maintaining a Healthy Weight

• To maintain weight at an appropriate level, daily kcal intake should not exceed daily kcal output.

• Many Americans take in more calories than they need, leading to excess energy being converted to fat and causing overweight.

• To lose weight, an overweight person needs to lower kcal intake and increase kcal output through physical activity.

• Fad diets may lead to rapid weight loss, but are often nutritionally unbalanced and difficult to maintain long-term.

• Permanent lifestyle changes, such as increasing physical activity and reducing portion sizes, are necessary for weight loss and maintenance.

• Behavior modification can lead to safe weight loss at a reasonable rate of ½ to 2 pounds per week

• Sensible eating is necessary for weight maintenance.

Disorders Associated with Obesity

Type 2 Diabetes:

• Type 2 diabetes is caused by impaired insulin production and insulin resistance.

• Insulin resistance causes the body's cells to fail to take up glucose, leading to high blood glucose levels and glucose in the urine.

• Type 2 diabetes is often seen in people who are obese, and dietary factors are believed to contribute to its development.

• A healthy diet, increased physical activity, and weight loss can improve insulin's ability to function properly in type 2 diabetics.

• Simple sugars in foods, such as candy and ice cream, and sugars from the digestion of starch in white bread and potatoes can contribute to the occurrence of type 2 diabetes.

• Chronically high insulin levels lead to insulin resistance, increased fat deposition, and a high level of fatty acids in the blood, which can lead to an increased risk for cardiovascular disease.

Cardiovascular Disease:

• Cardiovascular disease is among the leading causes of death in the United States.

• Cardiovascular disease is often due to the blockage of arteries by plaque, which contains saturated fats and cholesterol.

• LDL is considered "bad" because it carries cholesterol from the liver to the cells, while HDL is considered "good" because it carries cholesterol from the cells to the liver.

• Saturated fats, including trans fats, tend to raise LDL cholesterol levels, while unsaturated fats lower LDL cholesterol levels.

• Beef, dairy foods, and coconut oil are rich sources of saturated fat, while foods containing partially hydrogenated oils are sources of trans fats.

• Unsaturated fatty acids in olive and canola oils, most nuts, and coldwater fish tend to lower LDL cholesterol levels.

• Coldwater fish contain polyunsaturated fatty acids, especially omega-3 unsaturated fatty acids, which can reduce the risk for cardiovascular disease.

• Taking fish oil supplements to obtain omega-3 fatty acids is not recommended without a physician's approval.

• Dietary saturated fats and trans fats raise LDL cholesterol levels more than dietary cholesterol.

• Modifying the fat content of the diet, losing excess body fat, and exercising regularly can reduce blood lipid levels.

• If lifestyle changes do not lower blood lipid levels enough to reduce the risk for cardiovascular disease, a physician may prescribe medication.

Eating Disorders

• Many serious disorders in Americans are linked to a diet that results in excess body fat.

• In the United States, the number of people who are overweight or obese has reached epidemic proportions.

• Nearly two-thirds of adult Americans have too much body fat.

• Excess body fat increases the risk of type 2 diabetes, cardiovascular disease, and certain cancers.

• These conditions are among the leading causes of disability and death in the United States.

• It is important for us all to stay within the recommended weight for our height.

• People with eating disorders are dissatisfied with their body image.

• Social, cultural, emotional, and biological factors all contribute to the development of an eating disorder.

• These serious conditions can lead to malnutrition, disability, and death.

• Early recognition and treatment are crucial for all eating disorders.

• Treatment usually includes psychological counseling and antidepressant medications.

• Anorexia nervosa is a severe psychological disorder characterized by an irrational fear of getting fat.

• A self-imposed starvation diet is often accompanied by occasional binge eating, followed by purging and extreme physical activity to avoid weight gain.

• Binges usually include large amounts of high-calorie foods, and purging episodes involve self-induced vomiting and laxative abuse.

• About 90% of people suffering from anorexia nervosa are young women; an estimated 1 in 200 teenage girls is affected.

• A person with bulimia nervosa binge eats, then purges to avoid gaining weight.

• The binge-purge cyclic behavior can occur several times a day.

• People with bulimia nervosa can be difficult to identify because their body weight is often normal, and they tend to conceal their bingeing and purging practices.

• Women are more likely than men to develop bulimia; an estimated 4% of young women suffer from this condition.

• Other abnormal eating practices include binge-eating disorder and muscle dysmorphia.

• Many obese people suffer from binge-eating disorder, a condition characterized by episodes of overeating that are not followed by purging.

• Stress, anxiety, anger, and depression can trigger food binges.

• A person suffering from muscle dysmorphia thinks his or her body is underdeveloped.

• Body-building activities and a preoccupation with diet and body form accompany this condition.

• Unlike anorexia nervosa and bulimia, muscle dysmorphia affects more men than women.