HSC 4572: SELECTED

PORTIONS CHAPTER 6- PROTEINS

Valerie Schulz, MMSc, RD, LD/N, CDE

OBJECTIVES Compare essential to non-essential

amino acids State the outcome if essential amino

acids are missing Discuss various roles of protein in

humans Describe fate of amino acids/protein

consumed with sufficient carbohydrate vs a carb-poor diet

Identify major forms of protein malnutrition

Discuss why consuming too much protein is not recommended

Summarize advantages/risks of vegan diet

PROTEIN BASICS Amino acids (aa): links in the chains of

proteins General structure of amino acids:

(side

group) - varies

H–H-N – C – C–O-O-H

(amino H (acid group)

group)

The nitrogen (N) makes protein different from carbohydrates or fats

The side group makes each aa different, and more complex than carbs or fats

PROTEIN BASICS (review of what was learned in HUN 2002) Unlike CHO and fat, protein contains

___________ Each building block of protein, the

________ __________, bind with ___________ bonds.

Human bodies (can / cannot) make essential amino acids.

What makes one amino acid different from another? The ______ group

How many amino acids are there? ______

STRUCTURE OF PROTEINS(Pg 191; heading is ‘How do Amino Acids Build

Proteins?’) Primary sequence is determined by the

_____ blueprint.

Secondary structure caused by attractions of ___________ groups.

Tertiary structure caused by folding of the protein as electrically charged side groups are attracted to __________ and orient to the outside of protein. The side groups that have a neutral charge are repelled by water and attracted to each other; they tuck themselves _________ the protein structure.

DIGESTION, ABSORPTION OF PROTEINS

(Review of Chapter 3 – you tell me) Mouth: (does any protein digestion happen here?) Stomach: (2 things happen here)

Denatured/unfolded by ________ e_______________ break proteins into smaller chunks

Small intestine: many e_________, secreted into the small intestine by the pancreas or made in the small intestine, break up the chunks(don’t need to know specific names) Absorbed as ________ __________, into the blood

Large intestine: (does any protein absorption happen here?)

STRUCTURE OF PROTEINS Each human protein has a distinctive

sequence, leading to a specific 3-D shape and function.

The variety of possible sequences for amino acid strands is tremendous (compare 26 letters of alphabet, and how many words are in unabridged dictionary)

A single human cell may contain as many as 10,000 different proteins, each one present in thousands of copies.

PROTEIN STRUCTURE & FUNCTION

The following slide shows the hemoglobin molecule, exemplifying: 3-D structure of proteinsFunction is related to shape:

notice how the protein chains, shown in color, bend so that the heme molecule is held in place.

Iron atom is held by heme. Function of hemoglobin is to carry iron, & oxygen

Peer into the blue, green, purple and orange chains to see the primary sequence of the amino acids that determines the final shape of the protein, so it is perfect to carry heme

ABSORPTION OF PROTEINS Protein carriers transport amino acids into

the intestinal cells. The aa might be used in the intestinal cell for

its own purposes (intestinal cells are remade ~every 3 days)

If not needed in the intestinal cell, aa move on into the blood on the way to the liver.

Important point: EVERY protein we eat is broken down to amino acids before it is remade into human proteins. So we cannot eat an enzyme to help our digestion, because it would be denatured in the stomach.

NUTRIENTS AND GENE EXPRESSION

(Pg 194; the Variety of Proteins, Nutrients and Gene Expression)

Every cell nucleus contains the DNA for making __________ human protein, but cells do not make them all.Some genes are “expressed” and others are not

depending on the cell type. For example, only cells of the pancreas express the

gene for the protein hormone insulin.

Nutrients do not change DNA structure, but they greatly influence genetic expression

(will not be tested on protein synthesis, Figure 6.6, pg 195)

GENE EXPRESSION Those who suffered through HUN 2002

with me will remember the following cartoon slide

It likens the long strand of DNA to a “sentence”, and then considers the smaller gene piece as a “word” in that sentence

The blue part is the actual codes that stand for each amino acid

The green parts are the all important control areas, where what we eat will have an impact on how often (or not) this protein is expressed. (Like omega-3 fats causing more anti-inflammatory proteins to be made.)

PROTEIN SYNTHESIS: GENESGenes can be thought of as 'words' along the DNA 'sentences'.

ONE WAY TO CREATE DEFICIENCY

Amino acids with similar structures use the same transport systems to enter intestinal cells

As a result, amino acids may compete with one another for absorption, ie, excess of one may slow absorption of the other that uses the same system

When single amino acid supplements are consumed, the supplemented aa may overwhelm the transport system

This reduces the absorption of the other amino acids using the same system.

EXAMPLE OF CREATING DEFICIENCY

Joe takes an excess of amino acid “A”, which uses the same transport or carrier proteins as amino acids “B” and “C”

All the carrier proteins get filled up with “A”, because there is so much of it

There is not enough space on the carrier proteins to transport “B” or “C”, so less of those two are absorbed

Especially if “B” or “C” are essential amino acids, Joe will be creating a deficiency by taking an excess of “A”

ROLES OF PROTEINS IN BODY1. Building materials: for

growth/maintenance [muscle, collagen]2. Hormones: messengers; some are

proteins3. Regulators of fluid balance: proteins hold

water in the cells or in the plasma (blood). In protein malnutrition, blood levels fall too low, water ‘leaks out’ in between the cells, causing edema

4. Enzymes:1. Digestion (break down)2. Build (ex: bones)3. Transform (ex: amino acid into glucose)4. Enzyme action: figure 6-7 (changed from 6.9)

ROLES OF PROTEINS IN BODY1. Acid-Base regulators: proteins have

negatively charged surfaces, can attract loose H+ ions “buffers”

2. Transporters: 1. hemoglobin carries oxygen from lungs to all cells; 2. lipoproteins carry lipids in the watery blood; 3. special transport proteins carry vitamins & minerals

3. Antibodies: designed to destroy specific antigen (ex: virus)

4. Source of energy (glucose): gluconeogenesis – making glucose from protein

TRANSPORT PROTEIN: NA+, K+

PROVIDING ENERGY AND GLUCOSE

When insufficient carbohydrate and fat are consumed to meet the body’s energy need, food protein and body protein are sacrificed to supply energy.

The ____________ part is removed from each amino acid, and the resulting fragment is oxidized for energy.

No storage form of amino acids exists in the body.

PROVIDING ENERGY AND GLUCOSE

THE FATE OF AN AMINO ACID

When an amino acid arrives in a cell, it can be:Used as is to build proteinAltered somewhat to make another needed

compound, such as the vitamin niacinDismantled to use its amine group to build a

nonessential amino acid The remaining carbon, hydrogen and oxygen atoms

can be converted to glucose or fat

THE FATE OF AN AMINO ACID

In a cell starved for energy with no glucose or fatty acids:The cell strips the amino acid of its amine

group (nitrogen part) and uses the remainder of its structure for energy

The amine group is excreted from the cell and then from the body in the urine

THE FATE OF AN AMINO ACID

In a cell that has a surplus of energy and amino acids, the cell takes the amino acid apartexcretes the amine groupconverts the rest to glucose or fat for

storage

Amino acids are “wasted” (won’t be used as protein) when:

Energy is lacking from other sources (either not enough kcal and/or not enough carb).

Protein is overabundant (can’t store it)An amino acid is oversupplied in supplement

form.The quality of the diet’s protein is too low (too

few essential amino acids).

THE FATE OF AN AMINO ACID

© 2012 John Wiley & Sons, Inc. All rights reserved.

AMINO ACID POOL

FOOD PROTEIN: USE, QUALITY, AND NEED

To be used efficiently as protein, protein must be accompanied by: ample carbohydrate and fat (kcal) (“Protein-sparing” effect of carbohydrate) vitamins and minerals.

Protein quality is influenced by a protein’s digestibility and its amino acid composition.

Amino acids from animal proteins are most easily digested and absorbed (over 90%)

Amino acids from legumes are next (80 to 90%) Amino acids from plant foods vary (70 to 90%)

AMINO ACID COMPOSITION

High-quality proteins – provide enough of all of the essential amino acids needed to make new proteins

Low-quality proteins – do not provide all the essential amino acids If a nonessential amino acid is unavailable

from food, the cell synthesizes it If the diet fails to provide an essential amino

acid, the cells begin to conserve the amino acid and reduce their use of amino acids for fuel.

HOW DEFICIENCIES HAPPEN If a person does not consume all

essential amino acids needed, the body’s pools of essential amino acids will dwindle: First, blood and muscle proteins are

dismantled to provide the needed essential amino acids

Finally, body organs are compromised.

COMPLEMENTARY PROTEINS If food “A” lacks essential amino acids (if it

is a low-quality protein), then the amino acids in food “A” can be used only if essential amino acids are present from another source.

If food “A” is paired w/another low-quality protein food that fills in the gap, then the two together provide all essential amino acids, giving the same benefit as a high quality protein.

See following slide (you will not be tested on the names of the amino acids that are complementary, just know the concept)

COMPLEMENTARY PROTEINS

HOW MUCH PROTEIN DO PEOPLE REALLY NEED?

The DRI recommendation for protein intake depends on size and stage of growth

DRI recommended intake is 0.8 gram per kilogram of body weight per day

Minimum is 10 percent of total calories 2000 kcal x 10% = 200 kcal 200 kcal / 4 kcal per g protein = 50 g protein 50 g protein spread over 3 meals is ~15-20g/meal

Athletes may need slightly more (1g per kg)

NITROGEN BALANCE I just wanted you to be exposed to the

concept on the following slide It is used more in intensive care and

research situations than it would be in day-to-day nutrition care or education

NITROGEN BALANCE

CLINICAL OUTCOMES RELATED TO PROTEIN Now that we have covered all the basics

of protein, will consider the effects of lack of protein or too much protein on disease.

PROTEIN ENERGY MALNUTRITION PEM occurs in two main forms:

K___________________ (acute protein deficiency) M_____________ chronic food (protein & energy)

deficiency

PEM AT HOME

PEM is not unknown in the United States, where millions live on the edge of hunger. Inner cities Rural areas Some elderly people, especially those living alone Hungry and homeless children People suffering from anorexia nervosa People with wasting illnesses such as AIDS, cancer, or drug

and alcohol addictions GI issues that have slowed or stopped the intake of food:

esophageal strictures, intestinal blockages

MARASMUS VS KWASHIORKOR

Variable Marasmus Kwashiorkor

Onset Earlier, usually in first year

Later, after breast-feeding has stopped

Growth Failure significant Not much

Edema No yes

Blood protein concentration

Not much change Very low

Skin changes Not usually Red patches & boils

Fatty liver no yes

BODY FUNCTION CHANGES PEM

Marasmus - without adequate nutrition:Muscles, including heart, weaken Brain development in children stunted, learning

impaired Metabolism slows, body temperature is subnormal Person is apathetic, does as little activity as possible Growth ceases; child is no larger at 4 than was at 2 Digestive enzymes in short supply, intestinal cells

cannot replenish, absorption fails Blood proteins, incl hemoglobin, not produced:

anemia Antibodies degraded to provide amino acids for other

synthesis, leaving the person an easy target for infection, including ones that cause diarrhea

Infections w/PEM cause 2/3 of child death in developing world

BODY FUNCTION CHANGES PEM Kwashiorkor

Without severe wasting of body fatProteins that maintained fluid balance

diminished, fluid leaks out of blood, accumulates in belly and legs, resulting in edema

Skin loses elasticity, cracks; sores develop, fail to heal

Fatty liver, caused by lack of protein carriers to transport fat out of liver

Fatty liver loses some function, including ability to clear toxins, which accumulate, reducing appetite

OVERCONSUMPTION: KIDNEY DISEASE There is no benefit from eating excess

protein: Why? In human beings, a high-protein diet

increases the kidneys’ workload but this alone does not appear to damage healthy kidneys or cause kidney disease. (What does?)

In people with kidney problems, a high-protein diet may speed the kidneys’ decline.

People with Stage 1 – Stage 4 can slow progression to Stage 5 (dialysis) by eating lower protein.

KIDNEY DISEASE Diagnosed by comparing BUN with

creatinine to estimate GFR: glomerular filtration rate

According to the National Kidney Foundation, normal results range from 90 - 120 mL/min/1.73 m2. (not necessary to memorize)

GFR decreases with age Levels below 60 mL/min/1.73 m2 for 3 or

more months are a sign of chronic kidney disease (CKD)

GFR below 15 mL/min/1.73 m2 is a sign of kidney failure; requires immediate medical attention. Dialysis usually when GFR <7.

DIET IN CKD (STAGE 2 - EARLY) Eat a healthy diet: Include a variety of grains,

especially whole grains, fresh fruits and vegetables Choose a diet that is low in saturated fat and

cholesterol and moderate in total fats Limit intake of refined and processed foods high in

sugar and sodium Choose and prepare foods with less salt or high

sodium ingredients Aim for a healthy weight, consume adequate

calories and include physical activity each day Consume the DRI for vitamins and minerals Keep protein intake within the Daily Reference

Intake (DRI) level recommended for healthy people (0.8g/k)

(potassium ,phosphorus usually not restricted unless blood levels above normal)

DIET IN CKD (STAGE 4 - LATE) Including grains, fruits and vegetables, but limiting whole

grains and certain fruits and vegetables if blood tests show phosphorus or potassium levels are above normal.

A diet that is low in saturated fat and cholesterol Limiting intake of processed foods high in sodium; prepare

foods with less salt or high sodium ingredients. Aiming for a healthy weight by consuming adequate

calories, including physical activity Limiting protein intake to the level determined by the

dietitian’s assessment of individual needs (as low as 30g/day)

Consuming DRI for water soluble vitamins; C limited Vitamin D and iron may be tailored to individual

requirements. Limiting phosphorus if blood levels of phosphorus or PTH

are above normal. Limiting calcium if blood levels are above normal. Limiting potassium if blood levels are above normal.

LIVER FAILURE: CAUSES Alcohol abuse Drug-induced:

http://www.medicinenet.com/liver_disease/page2.htm#what_are_the_causes_of_liver_disease

(from above link): start reading at ‘What are the causes of liver disease?’, read down through alcohol abuse, cirrhosis. Under drug induced, just notice the part about acetaminophen. Start again at infectious hepatitis, then stop at hemochromatosis.

DIET IN LIVER FAILURE Limited amount of protein. A damaged liver cannot

process protein very well. This causes a build-up of ammonia in the bloodstream.

More carbohydrate. Carbohydrate is the body's energy supply. A healthy liver makes glycogen from carbohydrate. The glycogen is then broken down when the body needs energy. A damaged liver can't do this. Without glycogen, more carbohydrate is needed from the diet to make sure the body has enough energy.

A moderate amount of fat. Fat provides calories, essential fatty acids, and fat-soluble vitamins.

A limited amount of fluids and sodium. Liver damage can cause high blood pressure in the major vein of the liver. This can result in ascites, a fluid build-up in the abdominal cavity. Limiting fluids and sodium can help prevent this. (you saw the ascites picture in Chap 3 controversy on alcohol )

DIET IN LIVER FAILURE Common diet prescription for ESLD (End

stage liver disease): 30-60g protein (usually works out to 8-15% of

kcal); lower amounts if history of high blood ammonia, or encephalopathy. High quality protein is more desirable (why?)

60-70% kcal as carbohydrate; fruit is encouraged. Usually have to demonstrate how to add extra. Carbs do not need protein carriers for absorption.

25-30% kcal from fat (about same as is recommended for population at large). Fat needs protein carriers.

2gm (2000mg) Na+ or less. This is the difficult part to implement

Fluid restriction: not always

VEGETARIAN DIETS What constitutes a vegetarian diet?

Many subsets of reducing/omitting animal foodsDescribe varieties :

“flexitarian” Lacto-ovo Lacto vegan

People who eat well-planned vegetarian

diets suffer less often from chronic diseases than people whose diets center on meat

POSITIVE ASPECTS VEGETARIAN DIETS Strong evidence links vegetarian diets with

reduced incidences of chronic diseases. Benefits include: Less obesity Defense against certain cancers (colo-rectal

associated with red and processed meats. Fish eaters had lowest levels of cancer in a UK study)

Less heart disease (blood lipids stepwise: vegan, lacto-ovo, meat-eating)

Less high blood pressure (specific etiology unclear: lower body weight and higher K+ probable)

May help prevent diabetes, osteoporosis, diverticular disease, gallstones, and rheumatoid arthritis

REASONS FOR POSITIVE ASPECTS

When meat (animal muscle) is omitted, USUALLY see these changes:Lower saturated fat Increased whole grains (is whole wheat

bread a whole grain? You have discussed this!)

Increased fruit, vegetable, legumes - all associated with improved health

Positive changes associated with a vegetarian diet are the same changes associated with a WHOLE foods pattern of eating

POSITIVE ASPECTS OF EATING MEAT A balanced, adequate diet in which lean

meats and seafood, eggs, and milk play a part in addition to fruits, vegetables and whole grains can be very healthy.

On the other hand:Meat lovers who shun all vegetables have

no adequate substitutions for these foods (unlike vegetarians who can find suitable replacements for meat).

Both vegetarian and meat-containing diets, if not properly balanced, can lack nutrients.

Poorly planned meat eater’s diets may lack: vitamin A vitamin C Folate fiber

Poorly planned vegetarian diets typically lack: Iron Zinc Calcium omega-3 fatty acids vitamin D vitamin B12.

VEGETARIAN VS MEAT EATING

NUTRIENTS/AREAS OF CONCERN IN VEGETARIAN DIETS

Area Vegan Meat consuming

Pregnancy If start pregnancy too thin, need extra kcal. Choose well to get enough B12 and iron.

Receive enough B12, iron, zinc. If also consume dairy, usually enough Ca++, Vit D

Childhood Vegan foods higher fiber, child may get full before achieve all nutrients.

Same

Adolescence

Teens wisely choosing lots of fruits & vegs can meet national dietary objectives, rare in US. Iron still an issue.

Very easy to choose foods that exclude fruits and vegetables, initiate fatty streaks, etc.

Aging Softer cooked vegetable proteins aesthetically pleasing

Poor dentition leads to problems chewing meat; texture change not well liked.

FOOD SOURCES

Nutrient Vegan Meat consuming

Protein Legumes, seeds, nuts, soy

Animal muscle, egg, dairy

Iron Dark green leafy, dried fruits (hi kcal), legumes (w/ Vit C)

Animal muscle, egg (w/ Vit C)

Zinc Legumes, nuts, seeds Animal muscle, dairy

Calcium Dark green leafy, nuts, seeds (fortified plant milk)

Dairy

Omega-3

Marine algae, flaxseed, walnuts

Fatty fish