Chapter 6
The Proteins and Amino Acids
Nutrition: Concepts & Controversies, 12e
Sizer/Whitney
Learning Objectives
 Describe why some amino acids are
essential, nonessential, or conditionally
essential to the human body, and state the
outcome should any one of them be lacking
in the diet.
 Compare the digestion of protein and
transport of amino acids with digestion and
transport of lipids in the body.
 Discuss the roles that various proteins and
amino acids can play in the body.
Learning Objectives
 Describe the fate of amino acids consumed
with a balanced diet versus a carbohydratepoor diet.
 Discuss the concept of nitrogen balance
and compute the amount of protein needed
for a healthy college student.
Learning Objectives
 Identify the major forms of protein
malnutrition, and discuss reasons why
consuming too much protein is not
recommended.
 Summarize the health advantages and
nutritional risks of a vegan diet.
 Develop a lacto-ovo vegetarian diet plan
that meets all nutrient requirements for a
given individual.
The Structure of Proteins
 Difference from carbohydrates and fats
 Amino acids
 Carbon atom with amine group and acid
group
 Side chain
 Essential amino acids
 Conditionally essential
 Recycling
 Priority system
How Do Amino Acids Build
Proteins?
 Peptide bonds
 Link amino acids
 Strands of amino acids do not remain
straight
 Coils
 Folds
 Side chain electrical charge
 Activation
The Coiling and Folding of a
Protein Molecule
The Structure of Hemoglobin
The Variety of Proteins
 Protein shapes enable performance of
different tasks
 Examples
 Protein strands – alone or in association
 Inherited amino acid sequences
 Alterations to sequence
 Sickle-cell disease
 Nutrients and gene expression
Normal Red Blood Cells and
Sickle Cells
Protein Synthesis
Denaturation of Proteins
 Denaturing agents
 Digestion
 Stomach acid
 Dangers of
denaturation
Protein Digestion
 Stomach
 Denatures protein in food
 Uncoil protein’s strands
 Enzymes attack peptide bonds
 Small intestine
 Polypeptides
 Further break down
 Common misconceptions
A Dipeptide and Tripeptide
How Protein in Food Becomes
Amino Acids in the Body
Amino Acid Absorption
 Absorbed by cells of small intestine
 Larger molecules
 Hormones or allergens
 Separate sites for absorption
 Released into the bloodstream
 Carried to the liver
The Importance of Protein
 Amino acids must
be continually
available
 Building of new
proteins
 Amino acids are
needed each day
 Protein turnover
Roles of Body Proteins
 Regulation of gene expression
 Providing structure and movement
 Muscle tissue
 Other structural proteins
 Building enzymes, hormones, & other
compounds
 Building antibodies
Enzyme Action
Amino Acid Sequence of Human
Insulin
Roles of Body Proteins
 Transporting substances
 Hemoglobin and lipoproteins
 Maintaining fluid and electrolyte balance
 Edema
 Maintaining acid-base balance
 Blood clotting
 Providing energy and glucose
Proteins Transport Substances
Into and Out of Cells
Amino Acids to Glucose
 Protein can help maintain blood glucose
levels
 No storage compound for protein
 Dismantle tissue proteins
 Oversupply of amino acids
 Remove amine group
 Use of residues
Three Different Energy Sources
Amino Acids to Glucose
 Fate of an amino acid
 Cellular use
 Build protein
 Make a needed compound
 Dismantle amino acid for component parts
 Wasting of amino acids
 Preventing waste
Protein and Amino Acid
Supplements
 Protein supplements
 Do not improve performance
 Not effective for weight loss
 Amino acid supplements
 Body designed to work with whole proteins
 No safe level of amino acid supplementation
People Most Likely to Be Harmed
by Amino Acid Supplements
How Much Protein Do People
Really Need?
 DRI
 Depends on body size
 Infants and growing children
 Recommended intake
 Vegetarians
 Minimum amount
 Upper limit
 Body’s health
 Quality
Nitrogen Balance
 Nitrogen excreted as compared to nitrogen
eaten
 Levels in healthy adults
 Variation in nitrogen balance
 Positive balance
 Examples
 Negative balance
 Examples
Nitrogen Balance
Which Foods Provide High Quality
Protein?
 High-quality proteins
 Enough of all essential amino acids
 Limiting amino acids
 Complementary proteins
 Mutual supplementation
 Protein digestibility
 Animal proteins
 Legumes
Complementary Protein
Combinations
Protein Deficiency and Excess
 World’s leading form of malnutrition
 Combined with energy deficiencies
 Protein-energy malnutrition (PEM)
 Locations of prevalence
 Effects of PEM
 Children and adults
 Two forms
Protein Deficiency and Excess
 Marasmus
 Common in
children
 Muscle wasting
 Impairments
 Disease conditions
 Preventing death
 Heart failure
Protein Deficiency and Excess
 Kwashiorkor
 Weaning of babies
 Fluid balance is
diminished
 Changes in body
 Risk of infection
 PEM at home
Protein Deficiency and Excess
 Overconsumption of protein-rich foods
 Possible health risks
 U.S. protein intakes
 Heart disease
 Homocysteine
 Kidney disease
 Adult bone loss
 Cancer
Getting Enough but Not Too Much
Protein
 Protein-rich foods
 Protein is critical to nutrition
 Displacement of other necessary foods
 Advantages of legumes
 Protein
 Vitamin and mineral source
 Soybeans
Top Contributors of Protein to the
U.S. Diet
A Legume
Vegetarian and Meat-Containing
Diets: What Are the Benefits and
Pitfalls?
Controversy 6
Vegetarian Diets
 Reasons to choose a vegetarian lifestyle
 Categorization of vegetarians
 By foods they choose to eat
 Reasons why meat eaters choose to eat
meat
Terms Used to Describe
Vegetarians and Their Diets
Positive Health Aspects of
Vegetarian Diets
 Other health behaviors associated with
being vegetarian
 Obesity
 Heart disease
 Blood lipids
 Hypertension
 Cancer
 Other health benefits
Positive Health Aspects of the
Meat Eater’s Diet
 Critical times in life
 Examples




Pregnancy and infancy
Childhood
Adolescence
Aging
Planning a Vegetarian Diet
 Vegetarian food guides
 Ensure adequate intakes
 Protein
 Iron
 Zinc
 Calcium
 Vitamin B12
 Vitamin D
 Omega-3 fatty acids
My Vegetarian Food Pyramid
Nutrients in Nonfat Milk and Light
Soy Milk