chapter 18 nutrition

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Hole’s Human Anatomyand Physiology

Twelfth Edition

Shier Butler Lewis

Chapter 18

Nutrition and Metabolism

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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18.1: Introduction

• The human body requires fuel as well as materials to develop, grow and heal• Nutrients are chemical substances supplied by the environment required for survival

• Macronutrients• Carbohydrates• Proteins• Fats

• Micronutrients• Vitamins• Minerals

• Essential nutrients• Nutrients human cells cannot synthesize such as certain amino acids

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Fat cells

Bloodstream

Bloodstream

excessive

insufficient

Appetite

Appetite suppressed

Appetite enhanced

Fasting

+

+

++

+–

–

Stimulation

Inhibition

Adipocytes synthesizefat and secrete leptininto bloodstream

Leptin increasesmetabolic rate.

Food intake in excessof caloric needs

Leptin inhibits neuropeptideY release from thehypothalamus

Cells in stomachsecrete ghrelin

Ghrelin stimulates releaseof neuropeptide Y fromthe hypothalamus

Release intobloodstream

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18.2: Carbohydrates

• Carbohydrates are organic compounds and include the sugars and starches• The energy in their chemical bonds are used to power cellular processes• Excesses lead to:

• Obesity• Dental caries• Nutritional deficits

• Deficiencies lead to:• Metabolic acidosis• Weight loss

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Carbohydrate Sources

• Carbohydrates are ingested in a variety of forms:• Complex carbohydrates are polysaccharides that include:

• Starch from plant foods• Gylcogen from meats

• Simple carbohydrates are:• Dissaccharides from milk sugar, cane sugar, beet sugar and molasses• Monosaccharides from honey and fruits

• Digestion breaks complex carbohydrates into monosaccharides that are small enough to be absorbed• Cellulose is a complex carbohydrate abundant in our food

• It is not digested, but provides bulk (fiber or roughage)

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Carbohydrate Use

• Monosaccharides that are absorbed include fructose, galactose, and glucose


Glycogen Fat

Starch Sucrose Maltose Lactose

Carbohydrates

Digestion

Glucose Glucose

Monosaccharides

(Respiration) (Glycogenesis) (Lipogenesis)

Glucoseand

Fructose

Glucoseand

Galactose

CO2 + H2O + Energy

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Carbohydrate Requirements

• The minimal requirements for carbohydrates in the human diet is unknown• Intake of at least 125 – 175 grams is necessary• An average diet includes 200-300 grams

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18.3: Lipids

• Lipids are organic compounds that include fats, oils, and fat-like substances such as phospholipids and cholesterol• They supply energy for cellular processes and help to build structures like cell membranes• The most common dietary lipids are fats called triglycerides• Excesses lead to:

• Obesity• Increased serum cholesterol• Increased risk of heart diseases

• Deficiencies lead to: • Weight loss• Skin lesions• Hormonal imbalances

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Lipid Sources

• Triglycerides are found in plant-based and animal-based foods and include:

• From plants:• Seeds, nuts and plant oils (olive, peanut and canola are the healthiest)

• From animals:• Meat, eggs, milk and lard

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Lipid Use

• Lipids in foods are phospholipids, cholesterol and most commonly, fats (triglycerides)• They are oxidized for energy• They are stored in adipose tissue• Glycerol may be used to synthesize glucose

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Heat

CO2+

+

+Energy

Fats from foods

Fatty acids

Ketone bodies

Beta oxidation

GlycerolGlucose Fat

Hydrolysis

Citricacidcycle

H2O

ATP

Acetyl coenzyme A

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Cholesterol Phospholipids

Fatty acids + Glycerol

Digestion

Triglycerides

Triglycerides Lipoproteins Fatty acids(except essential

fatty acids)

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Lipid Requirements

• The lipid content of human diets varies widely• The American Heart Association advises that the diet not exceed 30% of total daily calories from fat

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18.4: Proteins• Proteins are polymers of amino acids• They have a wide variety of functions, including building more protein (structural protein, enzymes, hormones, and plasma proteins) and supplying energy• The waste product of protein metabolism is urea• Excesses lead to obesity• Deficiencies lead to:

• Extreme weight loss• Muscle wasting• Anemia• Growth retardation

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HormonesEnzymes

Proteins

Protein

Amino acids

Digestion

FatGlucose

Structuralproteins

Plasmaproteins

Energy + CO2 + H2O

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Heat

CO2+ +Energy

Proteins from foods

Amino acids

+

GlucoseFat

Urea

Hydrolysis

Deamination

–NH2 groupsDeaminated portions(by various pathways)

Acetylcoenzyme A

Citricacidcycle

H2O

ATP

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Protein Sources

• Foods rich in proteins include:• Meats• Fish• Poultry• Cheeses• Nuts• Milk• Eggs• Cereals• To some degree legumes (beans and peas)• The body needs 20 types of amino acids; those that can be synthesized by the body are non-essential amino acids (8) and those that cannot are essential amino acids (12)

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Nitrogen Balance

• In healthy adults, protein is continuously built up and broken down• Proteins contain a high percentage of nitrogen• The amount of nitrogen taken in is equal to amount excreted

• Negative nitrogen balance develops from starvation• Positive nitrogen balance develops in growing children, pregnant women, or an athlete in training

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Protein Requirements

• In addition to supplying essential amino acids, proteins provide nitrogen and other elements for the synthesis of non-essential amino acids and certain non-protein nitrogenous substances• The dietary amount varies according to body size, metabolic rate, and nitrogen balance condition• Typically protein intake is 10% of a person’s diet• Most people should consume 60-150 grams a day

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18.5: Energy Expenditures

• Carbohydrates, fats and proteins supply energy for all metabolic processes• Deficiencies can lead to death• Excesses can lead to obesity

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Energy Values of Food• A calorie indicates the amount of potential energy a food contains• Calories can be measured from the content of foods• The rate that the body expends energy can be measured and is known as basal metabolic rate (BMR)• This varies for:

• Carbohydrates• 4.1 calories per gram

• Lipids• 9.5 calories per gram

• Proteins• 4.1 calories per gram

Thermometer

Food sample

Insulation

Platinum dish

Stirrer

Oxygen

Electric wiresfor ignitionof sample

Water


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Energy Requirements

• Basal metabolic rate (BMR):• The rate at which body expends energy at rest • This primarily reflects energy needed to support the activities of the organs• This varies with gender, body size, body temperature, and endocrine function

• Energy is needed:• To maintain BMR• To support muscular activity• To maintain body temperature• For growth in children and pregnant women

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Energy Balance

• Energy balance occurs when caloric intake in the form of food equals caloric output from BMR and muscular activities• The body weight remains constant• If, however, caloric intake exceed output, tissues store excess nutrients• This is a positive energy balance that leads to weight gain

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Desirable Weight

• Most common nutritional disorders involve caloric imbalances

• Desirable weight is difficult to determine

• Body Mass Index (BMI) is used today to assess weight considering height

• A person is classified with BMI as either underweight, normal weight, overweight, or obese

• Overweight is defined as exceeding desirable weight by 10% - 20%, or a BMI of 25 and 30• Obesity occurs when a person is more than 20% above desired weight, or with a BMI over 30

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18.6: Vitamins

• Vitamins are organic compounds, other than carbohydrates, lipids and proteins, that are essential for normal metabolic processes

• Vitamins cannot be synthesized by body cells in adequate amounts

• Vitamins are classified on the basis of solubility as either fat- soluble (vitamins A, D, E, and K) or water-soluble (the B vitamins and vitamin C)

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Fat-Soluble Vitamins

• The fat-soluble vitamins dissolve in fats and are influenced by lipids

• Bile salts promote fat-soluble vitamin absorption

• They are fairly resistant to heat (not destroyed by cooking and/or food processing)

• Includes vitamins A, D, E, and K

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Water-Soluble Vitamins

• The water-soluble vitamins include the B vitamins and vitamin C

• Cooking and food processing destroy them

• B vitamins (six of them) are several compounds essential for normal cellular metabolism and known as the vitamin B complex

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18.7: Minerals

• Dietary minerals are inorganic elements that are essential in human metabolism

• These are usually extracted from the soil by plants

• They are obtained by humans from plant foods or animals that have eaten plants

• They are responsible for roughly 4% of body weight

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Characteristics of Minerals

• Minerals are most concentrated in the bones and teeth• They are typically incorporated into organic molecules (phospholipids, hemoglobin and iodine in thyroxine)• They compose parts of the structural materials of all cells• Homeostatic mechanisms regulate the concentration of minerals in body fluids• Mineral toxicity can result from too much of a mineral or from overexposure to industrial pollutants, household chemicals, or certain drugs

Major Minerals

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Trace Elements

• Trace elements (microminerals) are essential minerals found in minute amounts, each makes up less than 0.005% of body weight• They include:

• Iron• Manganese• Copper• Iodine• Cobalt• Zinc• Fluorine• Selenium• Chromium

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18.8: Healthy Eating• An adequate diet provides sufficient energy (calories), essential fatty acids, essential amino acids, vitamins, and minerals to support optimal growth and to maintain and repair body tissues• Requirements vary with age, sex, growth rate, level of physical activity and stress, and genetic and environmental factors• Dietary requirements such as recommended daily allowances (RDA) are best to follow• The U.S. Department of Agriculture’s Food Pyramid is another tool to follow• Nutritional information as well as ingredients are listed on most grocery items for retail sale

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Malnutrition

• Malnutrition is poor nutrition that results from a lack of essential nutrients or failure to use them

• Undernutrition – deficiency of essential nutrients• Overnutrition – excess of nutrient intake

• Malnutrition can be a result of:• Primary malnutrition – malnutrition from diet alone• Secondary malnutrition – adequate diet but individual characteristics make the diet insufficient

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Starvation

• A healthy human can survive 50-70 days without food• Symptoms include low blood pressure, slow pulse, chills, dry skin, hair loss, and poor immunity• Common nutritional disorders include:

• Marasmus – lack of all nutrients• Kwashiorkor – protein starvation• Anorexia nervosa – eating disorder; self-starvation• Bulimia – eating disorder; binge and purge cycle

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18.9: Lifespan Changes• Dietary requirements remain generally the same throughout life• BMR rises in early childhood and peaks in adolescence • BMR declines in adulthood• Change in nutrition often reflects the effects of medical conditions and the social and economic circumstances

Education

chapter 18 nutrition