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Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

The Proteins and Amino Acids

Chapter 6

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Learning Objectives

• Describe why some amino acids are essential, non-essential, or conditionally essential to the human body, and state the outcome should any one of them be lacking from the diet.
• Describe the digestion of protein and the absorption and transport of amino acids in the body.
• List the roles that various proteins and amino acids can play in the body, and describe the influence of carbohydrate on amino acid metabolism.
• Discuss the concept of nitrogen balance, and compute the amount of protein needed for a healthy college student.

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Learning Objectives

• Discuss potential physical problems from an eating plan that is too low or too high in protein.
• Identify protein-rich foods, and list some extra advantages associated with legumes.
• Summarize the health advantages and nutrition red flags of vegetarian diets, and develop a lacto-ovo vegetarian eating pattern that meets all nutrient requirements for a given individual.

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Protein

• Of prime importance
• Working proteins
• Enzymes, antibodies, transport vehicles, hormones
• Structural proteins
• Muscle tendons (muscle to bone), ligaments (bone to bone), hair, material of nails

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

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

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Essential Amino Acids

• The body cannot make these amino acids
• Without them, the body cannot make the proteins it needs to do this work
• We must eat these foods that provide the essential amino acids
• Non-essential amino acids
• Can be synthesized by the body

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Amino Acids

ESSENTIAL AA

• Histidine
• Isoleucine
• Leucine
• Lysine
• Methionine
• Phenylalanine
• Threonine
• Tryptophan
• Valine

NON-ESSENTIAL AA

• Alanine
• Arginine
• Asparagine
• Aspartic acid
• Cysteine
• Glutamic acid
• Glutamine
• Glycine
• Proline
• Serine
• Tyrosine

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Conditionally Essential Amino Acid

• An amino acids that is normally non-essential
• Under special circumstances, when the need for it exceeds that body’s ability to produce it, it must be supplied by the diet
• Example: phenylalanine  tyrosine
• The body normally makes tyrosine from phenylalanine
• If the diet fails to supply enough phenylalanine, or if the body cannot make the conversion (as in the case of phenylketonuria, PKU), then tyrosine becomes a conditionally essential amino acid

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Recycling Amino Acids

• The body can break down proteins and reuse those amino acids
• Body can now build the protein molecules it needs
• Cells can use amino acids for energy
• Discarding the nitrogen atoms as waste
• Provides access to an emergency fund of amino acids in times of fuel, glucose, or protein deprivation
• The body employs a priority system in selecting the tissue proteins to dismantle
• Used first are the small proteins of the blood and muscle
• Then the body may be forced to use as structural protein of the heart and other organs

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Amino Acids Important in Nutrition

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

How Do Amino Acids Build Proteins?

• Peptide bonds
• Link amino acids
• Amine group of one amino acid to the carboxyl group of the other amino acid
• Strands of amino acids do not remain straight
• Coils
• Folds
• Side chain electrical charge – attracts water
• No charge (neutral) – repels water
• May need a vitamin or mineral to activate it
• Iron - hemoglobin

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Different Amino Acids Join Together

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

A Variety of Proteins

• Globular proteins are water soluble
• Proteins of blood
• Some proteins form hollow balls
• Can carry and store materials in their interior
• Some proteins are more than 10x as long as they are wide
• Proteins of tendons
• Insoluble in water and very strong
• Some proteins are composed of more than a single amino acid chain
• Nutrients and gene expression

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Examples

• Collagen
• A protein from which connective tissues are made
• Scars, tendons, ligaments, and the foundations of bones and teeth
• Acts somewhat like glue between cells
• Insulin
• Helps regulate blood sugar
• Enzymes- a protein catalysts
• A catalyst is a substance that facilitates a chemical reaction without itself being altered
• Hemoglobin
• Composed of 4 protein strands
• Large, globular protein; packed into red blood cells, carries oxygen
• Each strand holds an iron atom

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

The Coiling and Folding of a Protein Molecule

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Nutrients Influence Genetic Expression

• Cells monitor nutrient concentrations in the fluids surrounding them
• Pancreas
• When blood glucose is overabundant, synthesizes insulin
• Results in a lowering of blood glucose concentration
• Hemoglobin
• Low iron => immature red blood cells respond by reducing hemoglobin synthesis
• Abundant iron => stimulates hemoglobin synthesis by immature red blood cells

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

The Structure of Hemoglobin

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Normal Red Blood Cells and Sickle Cells

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Protein Synthesis

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Denaturation of Proteins

• Change in shape of the protein
• First step in its destruction
• Denaturing agents
• Heat, acids, bases, alcohol
• Stomach – hydrochloric acid
• Cooking - heat
• Peptide bonds can now be broken

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Salts of Heavy Metals

• Many well-known poisons are salts of heavy metals such as mercury and silver
• These denature proteins whenever they touch them
• Common first-aid antidote for swallowing a heavy-metal poison
• Drink milk

The poison acts on the protein in the milk rather than on body protein

Vomiting can latter expel the milk-poison combination

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Protein Digestion

• Stomach
• Acid helps to denatures (uncoils) the protein’s tangled strands so that molecules of the stomach’s protein-digesting enzyme (pepsin) can attack the peptide bonds
• Small Intestine
• Receives a few are single amino acids
• Most are polypeptides
• 10+ amino acids bonded together

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Digestion

• Small Intestine
• Bicarbonate from the pancreas neutralizes the acid from stomach
• Protein-digesting enzymes
• Pancreas
• trypsin, chymotrypsin and carboxypolypeptidase
• Small intestine –peptidase –
• continues breaking down protein until nearly all that is left are dipeptides, tripeptides, or single amino acids

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

A Dipeptide and Tripeptide

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

How Protein in Food Becomes Amino Acids in the Body

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Amino Acid Absorption

• Single amino acids are absorbed
• Enzymes (peptidase) on their surfaces that split most tri- and dipeptides into single amino acids
• Cells of the small intestine
• Posses separate sites for absorbing different types of amino acids
• Amino acids may compete for the same absorption sites
• Thus, when a large dose of any single amino acid is ingested the absorption of other amino acids of the same general type may be limited

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

© 2006 Thomson-Wadsworth

Misleading and False Claims

• Don’t be mislead by advertisers urging, for example
• “Take enzyme A to help digest your food.”
• “Don’t eat food containing enzyme C, which will digest cells in your body.”
• Even the stomach’s digestive enzymes are denatured and absorbed when their jobs are through
• Another false claim
• Predigested proteins (amino acid supplements) are “easy to digest” and can therefore protect the digestive system from “overworking”
• The healthy digestive system handles whole proteins better than predigested ones

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

The Importance of Protein

• Amino acids must be continually available
• Building of new proteins
• Amino acids are needed each day
• Protein turnover

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Roles of Body Proteins

Regulation of gene expression

Providing structure and movement

Muscle tissue

Other structural proteins

Building enzymes, hormones, & other compounds

Tyrosine => thyroxine (thyroid hormone)

Tryptophan => seratonin (neurotransmitter) and niacin (vitamin)

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Enzyme Action

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Amino Acid Sequence of Human Insulin

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Roles of Body Proteins

Building antibodies - immunity

Transporting substances

• Hemoglobin and lipoproteins

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

The Roles of Body Proteins

Maintaining fluid and electrolyte balance

Albumin

Edema

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Roles of Body Proteins

Maintaining acid-base balance

Acidosis and alkalosis

Buffers keep a solutions acidity or alkalinity constant

Blood clotting

Providing energy and glucose

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Protein Energy

• Will be used for energy if it has to
• 4 kcal/gram
• When used for energy loses is amino group (NH2)
• Amino either used elsewhere or turned into urea by the liver
• Urea sent to kidney for excretion (urine)
• Fragments remain, C, H, O2 – can be used to build CHO and fats

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Amino Acids to Glucose

• Amino acids can be converted to glucose
• Can maintain blood glucose levels
• Can serve the glucose needs of the brain
• Amino acids can be converted to fat
• No storage compound for protein

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Fate of an Amino Acid

• Used to build protein
• Converted to other small nitrogen containing compounds such as niacin (a B vitamin)
• Converted to other amino acids
• Stripped of nitrogen, amino acids can be
• Converted to glucose
• Burned as fuel
• Stored as fat

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

The Macronutrients

For energy

• CHO offers energy
• Fats offer concentrated energy
• Proteins offer energy plus nitrogen

In storage

• Glucose stored as glycogen
• Fat stored as triglycerides
• Protein not stored – available only as active working molecular and structural components of tissue

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Three Different Energy Sources

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Activity: Practice Calculations

• 1. A food Item contains 5 grams of carbohydrate, 2 grams of fat and 3 grams of protein. How many calories does this product yield? ___________

• 2. A food contains 30 grams of CHO and 9 grams of fat, 20 grams of protein. How many calories does this product yield? __________

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Answer 1

• 5 grams of CHO x 4 kcal/gram = 20 kcal
• 2 grams of fat x 9 kcal/gram = 18 kcal
• 3 grams of protein x 4 kcal/gram = 12 kcal
• Total = 50 kcal

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Answer 2

• 30 grams of CHO x 4 kcal/gram = 120 kcal
• 9 grams of fat x 9 kcal/gram = 81 kcal
• 20 grams of protein x 4 kcal/gram = 80 kcal

• Total = 281 kcal

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

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
• How do you gain muscle?
• Think Fitness!

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

People Most Likely to Be Harmed by Amino Acid Supplements

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

How Much Protein Do People Really Need?

• DRI
• Adults: 0.8 grams per kg of body weight
• More athletic: 1.0-1.2 grams/kg body weight
• Adult women: 46 grams/day
• Adult males: 56 grams/day
• AMDR: 10-35% of kcal from protein
• USDA Food Guide MyPlate: HW due by Oct. 2, see Assignments tab)

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

How Much Protein?

• Body’s health
• Malnutrition
• Infection
• Other nutrients and energy
• Full array of macronutrients and micronutrients
• Quality
• Varied diet

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Nitrogen Balance

• Nitrogen excreted as compared to nitrogen eaten
• Levels in healthy adults
• Variation in nitrogen balance
• Positive balance
• Examples
• Negative balance
• Examples

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Nitrogen Balance

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Protein Quality

• High-quality proteins
• Enough of all essential amino acids
• Limiting amino acids
• Complementary proteins
• Mutual supplementation
• Protein digestibility
• Protein quality
• Animal proteins
• Legumes

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Complementary Protein Combinations

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Protein Digestibility

• Some proteins are more digestible than others
• Eggs vs. oats
• Perspective on quality proteins
• Meeting protein needs is not a problem for most people in the US, even if we were to eat no animal products at all
• Need to pay attention to mutual supplementation
• Varied, adequate in kcal, nutrient dense
• Malnutrition, limited protein => need to asses

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Too little protein?

• World’s leading form of malnutrition
• Protein combined with energy deficiencies
• Protein-energy malnutrition (PEM)
• Most widespread form of malnutrition in the world
• Two forms

Marasmus

Kwashiorkor

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Protein Deficiency

Marasmus

• Common in children 6-18 mo.
• Children fed weak cereal, low quality protein
• Wizened old person
• Muscle wasting
• Little body fat for insulation
• Hemoglobin, antibodies
• Dysentery – diarrhea
• Might progress to pt of no return

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Protein Deficiency

• Kwashiorkor – Ghanian – the evil spirit that infects the first child after the second child is born
• Weaning of babies from high-quality breastmilk
• Fluid balance is diminished
• Edema and fatty liver
• Risk of infection – liver cannot filter toxins
• PEM at home

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Protein Excess

• Overconsumption of protein-rich foods
• No health benefits, possible health risks
• U.S. protein intakes, sufficient
• Diets suggesting 65% protein unwarranted
• Heart disease
• Saturated fat
• Protein may raise levels of homocysteine
• Kidney disease
• Adult bone loss - osteoporosis
• Cancer of colon and rectum from well-cooked red meat and highly processed meats
• Low-gluten diet

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

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
• Tofu

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Top Contributors of Protein to the U.S. Diet

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

A Legume

• Protein rich foods
• The advantages of legumes
• Kidney bean, soybean, green peas, lentil, black-eyed peas, lima beans
• One cup of cooked legumes contain about 30% of the DV for both protein and iron
• Textured proteins fall short
• Tofu – calcium set

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Orecchiette with
broccoli rabe and tomatoes

Olive oil

Breadcrumbs

Coarse salt

Anchovy fillets

Garlic cloves

Capers

Cherry tomatoes

Red-pepper flakes

Broccoli rabe

Orecchiete pasta

WHERE DO THESE FOODS FIT ON MyPlate?

SEE NEXT SLIDE

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Vegetarian and Meat-Containing Diets: What Are the Benefits and Pitfalls?

Controversy 6

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Introduction

• Affluent countries
• Disease risk
• Benefits of vegetarian diets
• Vegetarian lifestyle
• Categorizes by foods they choose to eat

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Terms Used to Describe Vegetarian Diets

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Positive Health Aspects of Vegetarian Diets

• Other health behaviors associated with being vegetarian
• Obesity
• Heart disease
• Blood lipids
• Hypertension
• Cancer
• Other health benefits
• Diabetes, osteoporosis, diverticular disease

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Positive Health Aspects of the Meat Eater’s Diet

• Critical times in life
• Energy, B12, vitamin D, calcium, iron, omega 3, protein
• Pregnancy and infancy
• Childhood
• Adolescence
• Aging

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Choosing to be Vegetarian

Reasons include:

• A belief that we should not kill animals to eat their meat
• Many people don’t want to endorse the inhumane treatment of livestock
• Some believe we should eat less meat for health reasons
• Some believe we should eat less meat for environmental reasons
• Production of meat protein requires a much greater input of resources than does an equal amount of vegetable protein
• Some fear contracting diseases
• Such as food poisoning

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Planning a Vegetarian Diet

• Choosing within the food groups
• Protein foods group
• Oils group
• Milk products
• Convenience foods

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Filling the Vegetarian MyPlate

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

Planning a Vegetarian Diet

• Vegetarian food patterns
• Ensure adequate intakes
• Protein
• Iron
• Zinc
• Calcium
• Vitamin B12
• Vitamin D
• Omega-3 fatty acids

Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney

My Vegetarian Food Pyramid