Chapter 14 Nutrition: You Are What You Eat Copyright © 2013 by John Wiley & Sons, Inc. All rights...

Chapter 14

Nutrition: You Are What You Eat

Copyright © 2013 by John Wiley & Sons, Inc. All rights reserved.

Nutrients

© 2013 by John Wiley & Sons, Inc. All rights reserved.

• Nutrients are life-sustaining• The cells of our body require nutrients in usable form to maintain

homeostasis and create ATP• We cannot manufacture our own organic compounds, so we must

obtain them from the environment

Nutrients


• Two main types of nutrients– Macronutrients

• Carbohydrates, lipids, and proteins– Micronutrients

• Vitamins and minerals

• We require micronutrients – For the proper functioning of essential compounds– Such as the enzymes of cellular respiration

Macronutrients


• Three classes of macronutrients– Carbohydrates, fats, proteins

• We ingest carbohydrates, lipids, and proteins– To provide the necessary energy and material for the body to create its own

carbohydrates, lipids, and proteins• From these macronutrients, the body synthesizes cellular components like

– The cell membrane– Enzymes– Organelles– And even entirely new cells during cell division (mitosis and meiosis)

Carbohydrates are the Most Efficient Source of Energy


• Composed of – Carbon– Hydrogen– Oxygen– In a 1:2:1 ratio

• Glucose– Most common

carbohydrate– C6H12O6

• Our bodies are excellent at breaking down glucose – Produce ATP, amino

acids, glycogen, triglycerides

Lipids


• Lipids (fats) – Long chains of carbon and hydrogen molecules (hydrocarbon chains)– They have many more carbon atoms and far fewer oxygen atoms than do

carbohydrates

• Saturated Fats– Every space in the carbon chain is occupied with hydrogen atoms

• Unsaturated Fats– Fewer hydrogen atoms due to one or more double bonds in the carbon chain– Monounsaturated fat – has one double bond – Polyunsaturated fat – has more than one double bond

Lipids


• Double carbon-to-carbon bonds make kinks (bends) in the long hydrocarbon chains– Unsaturated fats cannot pack together tightly

• Are liquid at room temperature – i.e., vegetable oils – Saturated fats are straight and they pack tightly together

• Are solid at room temperature – i.e., animal fats, like butter and lard

• High-fat diets are high in calories, leading to obesity, which is associated with increased cancer risk– Saturated fats may increase cancer risk,– Other fats, such as omega-3 fats from fish oils, may reduce the risk of cancer

Lipids – Fatty Acids


Lipoproteins


• Fats are not soluble in water– Cannot be readily transported

through our watery blood

• They combine with proteins to form a lipoprotein– These lipoproteins can be

transported through watery blood– Main method for transporting

cholesterol through blood

Proteins


• Proteins are an essential part of our diet because the amino acids they contain are not stored in the body– Instead of completely breaking down the amino acids of ingested proteins for

energy, the body usually recycles them into proteins of its own

• Of the 20 amino acids that make up living organisms, we can manufacture only 11– The remaining essential amino acids must come from our diet

• Complete proteins, such as those found in red meat and fish, contain all 20 amino acids– No single vegetable or fruit contains all the essential amino acids– Must combine to get full complement

Food Groups


• Food groups are not nutrient classes– They are the major categories of foods– Meats, dairy products, breads and pastas, vegetables, and oils or fat

• Each group is important to overall health, and the recommended daily caloric intake for each group differs

• The food guide pyramid offers guidelines for the number of servings of each type of food that should be eaten each day

Food Groups


Micronutrients


• A healthy diet must include vitamins and minerals• Micronutrients are not broken down

– Used intact– Required for enzyme functioning or the synthesis of specific proteins

• Vitamins are organic substances– Such as thiamine, riboflavin, and vitamin A – Taking too large a quantity of fat-soluble vitamins can cause them to build up

in the liver, hampering its functioning• Minerals are inorganic substances

– Such as calcium, zinc, and iodine

Vitamins


Minerals


Metabolism

• The term metabolism refers to the chemical reactions in cells that break down and build up nutrients

• There are two basic kinds of metabolic reactions– Anabolic reactions

• Combine molecules into more complex compounds• Consuming more energy than it produces

– Catabolic reactions • Break molecules down• Producing more energy than it consumes

• Carbohydrates, lipids, and proteins undergo both anabolic and catabolic reactions


Cellular Respiration

• Carbohydrate catabolism (cellular respiration) – Is a controlled burning of the glucose molecule through a series of enzymatic

reactions that take place in our cells– We release the energy in foods through a process that involves sequentially

breaking chemical bonds– Carbohydrate metabolism releases energy gradually

• The first reaction is glycolysis– Occurs in the cell cytoplasm– Converts one glucose molecule into two pyruvate molecules

• Releasing a small amount of energy

• Second, – Assuming that oxygen is present, the pyruvates are then passed into a

mitochondrion (where oxidation continues)


• Third,— The mitochondrion completes the enzymatic burning of glucose by passing

the compounds through the Krebs cycle• In which energy rich compounds are created, and then passing these

compounds through the electron transport chain• These steps produce the carbon dioxide that we exhale

• Fourth,— Chemiosmosis within the inner membrane of the mitochondrion produces

most of the ATP used by cells— Also known as the electron transport chain



Glucose


• Most of the glucose in our bodies is catabolized (broken down) to make ATP

• Many glucose molecules combine to form glycogen– The only carbohydrate that is stored in our bodies– In the liver and skeletal muscles

• The hormone insulin– Joins glucose molecules together to form glycogen– A process called glycogenesis

Glucose


• Like carbohydrates, lipids, can be oxidized to produce ATP• If the body lacks carbohydrates, it mobilizes fat stores and converts fat

into small molecules called ketones• As ketones are oxidized to produce ATP

– Their concentration in the blood can rise above normal levels• The body may enter a metabolic state called ketosis• Extreme ketosis can lead to acidosis, in which the pH of blood becomes

very low (acidic)• Acidosis is serious—it can lead to a coma or even death

Lipid Storage

• Just as we can catabolize lipids for energy, we can also synthesize and store them

• When we consume more calories than are needed to meet our ATP needs– The body converts excess glucose into lipids called triglycerides– These are commonly stored in our fat cells (adipose cells or adipocytes)– Forming fat deposits


Energy

• The amount of energy coming into our bodies is directly related to the food we eat– Energy input should match energy output

• When the amount of energy provided by all the nutrients taken in by the body matches the amount of energy it expends– The body weight remains constant – This is known as energy homeostasis

• When the two amounts don’t match– We either gain or lose weight


Energy


Nutritional Disorders

• Weight loss– Anorexia nervosa – Bulimia nervosa

• Weight gain– Obesity– Usually defined in terms of body mass index (BMI)– To calculate BMI

• Divide weight in kilograms by the square of your height in meters


Body Mass Index - BMI


• BMI gives an indication of how much weight is due to fat stored in adipose tissue – If you are muscular or have denser or lighter bones than average, your BMI

may not be an accurate indication of obesity

• BMI is a rough estimate of the amount of body fat present – BMI between 18.5 and 24.9 is considered “normal and healthy” – BMI below 18.5 is labeled as underweight – BMI above 30 is labeled as obese

Body Mass Index - BMI


Food-Borne Disease

• More than 250 food-borne diseases are known– Ranging from bacteria and viruses to parasites and toxins contained in the

foods themselves

• The many types of food poisoning share a common thread– The causative pathogens are usually found growing in or on the foods we eat

• Symptoms vary– Nausea– Vomiting– Abdominal cramps– Diarrhea


Bacteria

• There are three common types of bacteria that can cause food poisoning – Campylobacter– Salmonella– Escherichia coli (E. coli)

• Campylobacter is a normal resident of the intestinal tract of chickens and other fowl– Commonly ingested in undercooked poultry– Primary cause of bacterial diarrhea

• Salmonella, found in the intestines of birds, reptiles, and mammals– Causes usual food poisoning symptoms but can become much more serious if

untreated– Salmonella can escape from the intestinal tract and enter the bloodstream

• Leading to septicemia - a life-threatening condition in which the blood carries a poison throughout the body


Bacteria

• E. coli is normally present in the colon of cattle, pigs, and humans– Inside the gastrointestinal tract, almost all E. coli are helpful or harmless

• E. coli infections can cause serious illness or outbreaks that sweep entire small towns– Many human infections come from meat that has been contaminated by the

contents of cattle intestines at the slaughterhouse– Water supplies near dairy industries also may become tainted– Ground beef is a common carrier because the bacteria can reside deep inside

the meat, where it cannot be washed off or easily heat-sterilized by cooking– Tainted spinach is a result of watering with reclaimed water that has not been

properly sterilized before being sprayed onto the crops


Viruses

• The most common viral food contaminant is calicivirus, or Norwalk-like virus– Causes vomiting that lasts for approximately two days, with little diarrhea or

fever – Norwalk-like virus has spread through the general population

• From fishers who have become infected through their oyster catch

• Stomach flu has similar symptoms– It is actually not influenza but, rather, a viral infection that attacks and irritates

the stomach and small intestine– Transmitted through kissing, touching, sharing food, drinks, or utensils– Food preparation workers who carry the virus can spread it through the food

they handle


Food Shortages

• Severe food shortages exist in many parts of the world– They occur primarily in developing countries as environmental, economic, and

social hardships often force people to abandon their homes and their livelihoods

– It is often difficult to import food for these migrating masses because of obstacles created by warfare, drought, or other natural disasters

• The resulting mass starvation and malnutrition puts serious strains on already impoverished countries


Malnutrition

• Malnutrition literally means “bad nutrients” – Caused by an inadequate diet – Lacking in calories or low in specific vitamins and minerals

• Malnutrition can also be due to– Infections that cause vomiting or diarrhea

• Which result in the loss of previously ingested nutrients

• In developing countries– Malnutrition accounts for many deaths - especially of infants and the elderly– Can produce substantially lower intelligence in those who survive


Kwashiorkor

• A distended belly is indicative of kwashiorkor, a series of complications resulting from protein deficiency in children– Children are taking in enough calories but are lacking in essential amino acids– Protein energy malnutrition (PEM) and micronutrient malnutrition are

common causes of kwashiorkor– Often simply restoring a healthy diet can alleviate the symptoms of

malnutrition– If a child has passed certain developmental stages, however, permanent

damage may result


Chapter 14 Nutrition: You Are What You Eat Copyright © 2013 by John Wiley & Sons, Inc. All rights...

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