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Chapter 25

Lecture Outline

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Living Things as Chemical Factories: Matter and Energy Manipulators

All organisms need energy and building blocks to live and grow.

Nutrients– All of the molecules required to support life– Includes inorganic elements and organic

molecules

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Diet and Nutrition Defined

Nutrition– The branch of science that studies food, its

nutrients, and how nutrients are used in the body– Also refers to the process by which we take in

food and utilize it

Diet– All of the food and drink consumed by an

organism

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The Process of Nutrition

Ingestion– Taking food into the body through eating

Digestion– The breakdown of complex food molecules to smaller

molecules

Absorption– The movement of smaller molecules from the digestive

system to the circulatory system

Assimilation– The modification and incorporation of absorbed

molecules into the structure of the organism

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Kinds of Nutrients and Their Function

Nutrients are divided into six major categories:– Carbohydrates– Lipids– Vitamins– Minerals– Water

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Energy Content of Food

calorie is a unit of energy—the energy needed to raise the temperature of a gram of water one degree Celsius

Kilocalorie=1000 calories The food calorie is a kilocalorie but is often

shown as Calorie (with a upper case C)

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Kinds of Nutrients and Their Function—Carbohydrates

Nutritionally important kinds of carbohydrates– Sugars

Simple sugars are the building blocks of complex carbohydrates

Mono- and disaccharides Glucose is a monosaccharide, sucrose is a

disaccharide

– Starch is a large polysaccharide made of many glucose molecules attached to one another.

– Fiber—complex indigestible carbohydrates

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Carbohydrates—Functions

Sugars and starch provide energy.– Disaccharides and starch are broken down to

simple sugars.– 4 Calories (kilocalories) in a gram of sugar

Sugars taste sweet and stimulate appetite. Simple sugars are building blocks of other

important molecules—DNA.

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Carbohydrates—Functions

Dietary fiber– Cellulose and other complex carbohydrates that

are Indigestible Slows absorption Stimulates peristalsis Reduces absorption of cholesterol Retains moisture in intestine—reduces incidence of

constipation

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Carbohydrate Quality

Foods made from refined flours and sugars provide Calories but little else (“empty Calories”)

Whole grain flours contain parts of seeds other than just starch and sugar– Dietary fiber– Other nutrients

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How the Body Manages Carbohydrates

Body stores the energy from carbohydrates in two ways

– Glycogen Glycogen is stored in liver and muscles. Glycogen consists of glucose molecules hooked together. Glycogen can be broken down to glucose as needed. Only small amounts of glycogen are stored.

– Fat Carbohydrates converted to fat for longer term storage.

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Kinds of Nutrients and Their Function—Lipids

Three kinds of lipids– Phospholipids are important parts of cell

membranes.– Steroids

Many steroids are hormones. Cholesterol is a steroid.

– True fats (triglycerides)

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Function of Fats

Long term storage of energy Excellent source of energy—release 9 Calories per

gram Vitamins A, D, E, and K dissolve in fats and will not be

absorbed unless fat is present. Fat under the skin serves as insulation. Fat under skin and around organs is a shock absorber. Fats provide a pleasant “mouth feel” to food and

provide a feeling of fullness in the stomach.

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Kinds of Fats Important in Nutrition

Saturated fats– No double bonds in fatty acid portion of molecule– Typically found in foods of animal origin– Solids at room temperature

Unsaturated– Double bonds in fatty acid portion of molecule– Typically found in foods of plant origin– Liquids at room temperature (oils)

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Kinds of Fats Important in Nutrition

Polyunsaturated fats– Have several double bonds in the fatty acid

portion of the molecule Trans fats

– Not normally found in natural foods– Created when unsaturated fats are converted to

saturated fats industrially Essential fatty acids (linoleic acid and linolenic acid)

must be obtain in the diet.

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How the Body Manages Fat

Fat is produced and stored when food consumption exceeds energy needs.

Energy from stored fat can be released when needed.

Originally this was a valuable mechanism to provide energy in a time of food scarcity.

Today most people rarely experience food scarcity and tend to permanently store fat (obesity).

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Kinds of Nutrients and Their Function—Proteins

Composed of amino acids hooked end to end Functions

– Enzymes– Structure—connective tissue, muscles, skin– Component of cell membranes– Some are hormones– Antibodies– Sending and receiving signals– Emergency source of energy if the body runs out of

carbohydrate and fat

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Kinds of Proteins

Complete proteins– Contain all of the amino acids necessary for good

health– Most proteins from animal sources are complete

proteins Incomplete proteins

– Lack certain amino acids needed by the body– Typical of proteins from plant sources

Essential amino acids– Cannot be made by the human body– Must be obtained from the diet

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Sources of Essential Amino Acids

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How the Body Manages Protein

Proteins cannot be stored and used later. Only small amounts of protein are lost each

day.– Therefore, we only need a small amount of

protein in our diet every day.– Typically 50 grams is adequate.– Protein consumed in excess of needs are

metabolized to provide energy.

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How the Body Manages Protein

Protein-sparing mechanism– During fasting or starvation our bodies oxidize

sugar and fats for energy before proteins.– Certain tissues cannot use fats for energy—red

blood cells, nerve cells. Amino acids must be converted to glucose for their

use.

– Long-term fasting or starvation is fatal because proteins essential for other uses are metabolized to provide glucose.

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Starvation and Stored Foods

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Kinds of Nutrients and Their Function—Vitamins

Organic molecules needed in small amounts to help enzymes work properly—cannot be made by humans

Participate in various metabolic reactions often as coenzymes

Many are antioxidants that destroy free radicals.

Most are acquired from food– Vitamin D is made in our bodies when UV light

hits cholesterol.

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Kinds of Vitamins

Water soluble vitamins– Vitamin C and various B vitamins

Fat soluble vitamins– Vitamins A, D, E, K, D

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How Vitamins Are Managed in the Body

Water soluble vitamins are not stored.– Must be obtain daily in the diet

Fat soluble vitamins can be stored in liver.– Released as needed

Vitamin supplements – Usually not needed if one eats a well-balanced diet

Megadoses of vitamins are not shown to be helpful.– Excess vitamins are excreted.– Some vitamins become toxic in high doses.

Vitamin-deficiency diseases are most common in poor countries with poverty and starvation.

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Sources and Functions of Vitamins

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Kinds of Nutrients and Their Function—Minerals

Inorganic elementsCannot be synthesized by the bodyNot altered by cookingPresent in various foods and drinking

water

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Kinds of Nutrients and Their Function—Minerals

Functions– Enzyme regulators and cofactors

Magnesium– Involved in neurotransmission

Sodium, potassium– Oxygen transport

Iron Anemia-iron deficiency

– Bone structure Calcium Osteoporosis-calcium deficiency

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Management of Minerals in the Body

Minerals are constantly lost from the body and must be replaced on a daily basis.

Most minerals are easily replaced with a reasonable diet.

Iron and calcium supplements are often needed, particularly in women.

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Sources and Functions of Minerals

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Kinds of Nutrients and Their Function—Water

The human body is 65% water. Primary component of blood, lymph, and

tissue fluid Dissolves

– Inorganic ions (Na+, K+, Cl-) Called electrolytes because they conduct electricity

when dissolved Organic molecules

– Many wastes are soluble in water, allowing for easy elimination.

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Kinds of Nutrients and Their Function—Water

Most chemical reactions in organisms occur in water.

Water is involved as a reactant in many important metabolic reactions. – Hydrolysis of carbohydrates, fats, proteins

Evaporation of water from skin provides cooling.

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Managing Water in the Body

Water is constantly lost.– Perspiration– Evaporation from skin and lungs– Urine and feces

Must be replaced continuously by ingesting water and foods containing water

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Dietary Reference Intakes

Published by the USDA Guidelines for maintaining good health

– Specific guidelines for men, women, children, pregnant, and nursing women, etc.

– Provide guidelines about maximum amounts of certain nutrients

Used in preparing food labels– Labels list ingredients from greatest to least in

quantity.

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Dietary Reference Intakes for Some Common Nutrients

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The Food Guide Pyramid

A simple diet guide using food groups

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The Food Guide Pyramid—Grains

Includes vitamin-enriched or whole-grain cereal

– Breads, bagels, cereals, crackers, pasta, etc.

Recommended amounts– Women - 6 oz.– Men - 8 oz.– 1 slice of bread = 1 oz.

● Should provide most of Calories in the diet● Whole grains are the best.

– Provide fiber that facilitates digestion– Satisfy appetite

●Grains also provide certain vitamins and minerals

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The Food Guide Pyramid—Fruits

Fruit is a botanical term for an enlarged or modified ovary of a plant

Nutritionally, a fruit is classified as any plant product that is sweet and not eaten during the main meal.– Melons, berries, apples, oranges,

and bananas 1–2 cups per day are recommended. Nutritional value

– Fiber– Water– Carbohydrate– Certain vitamins and minerals

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The Food Guide Pyramid–Vegetables

Nutritionally defined as plant material that is not sweet and is eaten with the main meal.

4.5 cups a day are recommended. Include

– Broccoli, carrots, cabbage, corn, green beans, lettuce, tomatoes, potatoes, etc

– Raw leafy greens important Significant value

– Cancer protection– Vitamins and minerals– Provide fiber– Carbohydrate

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The Food Guide Pyramid—Milk

Includes milk, cheese, yogurt, ice cream

2–3 cups/day recommended.– 1.5 oz. cheese = to one cup.

Many milk products are high in cholesterol and fat—use low fat products

Significant nutrient value– Protein, carbohydrate, fat– Calcium, potassium– Vitamin D, some B vitamins– Vitamin A added to some

milk

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The Food Guide Pyramid—Meatand Beans

Usually our main source of protein Includes beef, chicken, fish, nuts, beans, peas,

tofu, eggs 5.5–6.5 oz. per day are recommended. Daily intake is needed since protein cannot be stored. Animal proteins are complete proteins. Plant proteins are incomplete proteins. Significant nutrient information

– Prepare meats to eliminate fats– Mix different plant proteins sources

to get complete protein– Essential fatty acids from plants and fish– Certain minerals and vitamins

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The Food Guide Pyramid—Oils

6–7 teaspoons per day needed to obtain essential fatty acids

Have high caloric content– Must be eaten in moderation– Fats should comprise 20–35%

of total calories eaten in a day. Unsaturated is better than saturated

– Fish, nuts, vegetable oils are unsaturated.– Saturated fats, trans fats, and cholesterol

should be as low as possible.– Use lean meats and cook to eliminate fat.– Fats are a source of vitamin E.

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The Food Guide Pyramid—Exercise

2/3 of American adults are overweight and 1/3 are obese.

Exercise affects the number of food calories that can be consumed without gaining weight.

30 minutes of moderate exercise a day is recommended.

Moderate exercise will elevate heart rate significantly.

Longer and more vigorous exercise has additional benefits.

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Typical Energy Requirement for Common Activities

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Basal Metabolic Rate, Diet, and Weight Control

Basal metabolic rate is the energy need to maintain breathing, heart rate, digestion, and body temperature while at rest.

– Highly variable– Most people have a basal metabolic rate in the range of

1,200–2,200 Calories per day. Specific dynamic action is the energy needed to

process the food we eat. Voluntary muscle activity is the energy needed to

perform all voluntary activities. To maintain body weight the energy intake should be

equal to basal metabolism + specific dynamic action + voluntary muscle activity

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Additional Kilocalories Needed by Occupation

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Body Mass Index (BMI)

The USDA has published guidelines that will help people evaluate their weight.

– Educates people about the dangers of obesity Body mass index

– Evaluates weight based on height– Calculated by dividing weight in kilograms divided by height

in meters squared Obesity

– A BMI of over 30kg/m2 is considered obese. Drawback: BMI doesn’t measure fitness

– A measure of how efficiently a person can function physically and mentally

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Eating Disorders

Three most common problems associated with diet and food consumption are– Obesity– Bulimia– Anorexia nervosa

All these conditions involve issues related to metabolic rate, culture, and psychology.

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Obesity

Obesity is a condition of being overweight to the point that a person’s health, quality of life, or life span is adversely affected.

About 30% of U.S. population is obese. Obesity is defined as having a body mass index of

30 kg/m2 or greater. Body mass index (BMI) is determined by dividing a

person’s weight in kilograms (without clothes) by their height in meters squared.

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Body Mass Index

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Contributing Causes to Obesity

Psychological factors– Eating is a pleasurable activity.– Overeating is often associated with depression.

Genetic and metabolic differences– “Obesity genes” have been identified in mice.– People differ in metabolic rates.– Some people have a faulty mechanism that

normally causes people to “turn off” their appetite when they are full.

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Obesity

The condition of being overweight to the point where a person’s health and lifespan are adversely threatened

– Occurs when people eat more calories than they use Individuals who have a BMI of 30 or more are obese. Incidence is increasing because our activity level is

decreasing.– Sedentary death syndrome– Due to cultural and social factors– Genetic studies also indicate there may be a genetic

component to obesity.– May involve a chemical imbalance in the brain

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Bulimia

A disease involving a cycle of eating binges followed by purging the body of food– Purging may involve vomiting or the use of

laxatives or diuretics. Caused by psychological factors

– Can involve depression The binge-purge cycle has several negative

health effects.– Dehydration, diminished blood volume, mineral

deficiencies, kidney malfunction, lethargy, etc.

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Anorexia Nervosa

A nutritional deficiency disease characterized by severe, prolonged weight loss

– Involves voluntary, severe restriction of caloric intake

Caused by an extreme fear of becoming overweight– Anorexics have a distorted perception of their body.

Severe caloric deficiency (starvation) results in– Hair loss, constipation, amenorrhea, decreased heart rate,

osteoporosis, etc.

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Nutrition During Infancy

A person’s total energy needs per kg are greatest during the first year of life.

50% of an infant’s caloric intake is used to maintain its basal metabolic rate.

Infants triple their weight and increase 50% in height over the first year of life.– Therefore, they need nutritionally rich food with

high caloric value.

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Human Breast Milk vs. Cow’s Milk

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Osteoporosis

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Nutrition for Fitness and Sports

Cellular respiration mobilizes the energy needed for exercise.

– Makes the ATP needed for muscle contraction– Uses glucose, fatty acids, or amino acids

Glucose from stored glycogen is used first. Fatty acids from stored triglycerides is used next. Amino acids are rarely utilized during exercise.

Conditioning– Improves strength of muscles and heart – Improves coordination of muscle movements– Increases metabolic rate

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Anaerobic Exercise

Bouts of exercise that are so intense that the muscles cannot get oxygen as fast as they need it

Glycolysis provides the ATP (since oxygen is not present).

Only glucose and glycogen can be used.

Lactic acid buildup in muscles

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Aerobic Exercise

When the level of exertion allows the heart and lungs to keep up with the oxygen demand of the muscles

Aerobic cellular respiration provides the ATP needed.

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Metabolic Changes during Aerobic Exercise

Warm-up period increases metabolic rate, heart rate, and temperature which provides better blood flow to muscles

At the beginning of exercise anaerobic respiration provides ATP as glucose and glycogen is used.

Shift to aerobic exercise after initial anaerobic period (second wind)

– Begin to metabolize triglycerides to provide ATP– Continue to use glycogen– When glycogen stores are depleted, athletes “hit the

wall”. A cool-down period allows metabolic shifts back normal.

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Diet and Training

Water intake is very important during exercise.– Needed to cool the body– Loss results in more viscous (thicker) blood

Long-term exercise requires the consumption of high calorie foods.

Carbohydrate loading can help prevent “hitting the wall”.

– Eat high carbohydrate foods in days before event.– Used in conjunction with training exercise

High protein diets not necessary during training

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Diet and Training

Protein supplementation– Eating additional proteins will not result in an

increase in muscle mass unless one is exercising and placing demands on the muscles.

Water intake– Water loss can decrease muscular activity.– Drinking water before and during exercise is

necessary to prevent dehydration.