Proteins and Amino Acids in Nutrition Dr. David L. Gee FCSN 245 Basic Nutrition

Proteins and Amino Acids in Nutrition

Dr. David L. Gee

FCSN 245

Basic Nutrition

Biologically:– proteins are the most important

molecues in the body “action molecues”

Nutritionally: (at least in the US)– proteins are of the least concern for

macronutrients in the diet protein deficiency very unusual excess protein generally not a problem

©2001 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.

Protein Structure

Polymer of amino acidsAmino acid structure

–amino group (N)

–acid group

–side chain




Amino Acids 20 different amino acids

– Differ by type of side chain Water soluble AA

– charged side groups Can form ionic bonds

– sulfer containing side groups Can form disulfide bonds

Fat soluble AA– Fat soluble AA interact/dissolve with each other

These interaction/bonds between AA side chains cause proteins to form specific shapes

Protein StructurePrimary Structure

–sequence of amino acidsSecondary Structure

–helical coil

Protein StructureTertiary Structure

– folding of coil

– 3-dimensional structureDetermined by AA sequence Specificity of a protein’s

functionDiversity of protein functions

Other Amino Acid Facts

9 “Essential” amino acids– Amino acids that cannot be made and must be

consumed in the diet (dietary essential) peptide bonds link amino acids together proteins typically contain a few hundred

amino acids– infinite combinations of amino acids– tremendous diversity of protein types

Protein Synthesis:how proteins are made

DNA, genes, chromosomes– where the information is stored

“Transcription”– making a copy of the information

– messenger RNA

“Translation” – reading the information and making the protein



Genetic Disorders:errors in the stored information

Examples:– Sickle Cell Anemia– Cystic Fibrosis– Familial Hypercholesterolemia

LDL-receptor

Human Genome Project– Map the genome

20-25,000 genes in human genome (10/04)

– Fix the genes ???

Have you eaten GM foods?Are GM foods safe?

2003 survey of US consumers– Non-partisan Pew Initiative on Food and

Biotechnology

48 % opposed to GM foods, 25% in favor– 2001 58% opposed to GM foods

24% say they’ve eaten GM foods– 58% say they haven’t

Genetic Modified Crops: Prevalence

In 2003 (USDA) genetically modified crops accounted for:– 40% of all corn– 81% of soybeans– 73% of cotton

In 2002– 35% of corn– 55% of soybeans

Grocery Manufactures of America (2003)– 70-80% of processed foods contain GMO

USDA approval for– potatoes, tomatoes, melons, beets– nicotine free tobacco

Genetic Engineering:Food and Health Issues

Traditional animal and plant breedingAlteration of genetic material with tools

of biotechnologyAdvantages:

– speed– more specific, less random– interspecies gene transfer

Benefits of Genetically Engineered Foods

Reduce use of pesticidesBacillus thuringiensis (Bt)

– “natural” pesticide used by organic farmers– Bt produces a protein toxic to insect larvae

Gene for Bt toxin incorporated into corn, etc.– Corn plant produces Bt protein toxin


Reduce erosion of topsoil due to tilling– tilling for weed control

Monsanto’s “Roundup” (glyphosate)– inhibits plant’s ability to make tryptophan

– tryptophan is an EAA for humans

Roundup resistant plants (soybeans)– spliced bacterial gene into plant that is resistant to

effect of Roundup (still able to make tryptophan)


Improved nutritional quality of plants– “golden rice”

rice with B-carotene gene

– improved protein quality & quantity– higher in vitamins

Improved sensory properties– Tomato and strawberry flavor & texture

Genetically Engineered Foods:

Environmental Concerns Pesticide resistant insectsUnintentional environmental effects

– monarch butterfly larvae - lab study– affect beneficial insects (ladybugs)– development of “superweeds”, “superbugs”

Control of Food Production– Terminator gene

GMO plants with gene to produce sterile seeds

– Biotech firms with too much control?

Genetically Engineered Foods:

Health Issues(Theoretical problems?)

Lack of long term feeding trials– animal studies, human studies

Food allergies– antifreeze protein from fish

Labeling Issue– Pros: consumer has the right to know– Cons: unnecessary, no evidence of

environmental/health concerns, will hurt sales and stymie further development

Protein FunctionsEnzymes & related proteins

– Catalysts

– Membrane transporters

– Cell receptors


Transport Proteinssodium pumps

Protein FunctionsStructural Proteins

–Muscle fiber proteins

–Connective proteins

Protein FunctionsHormonesProtein Hormones

– Insulin

– GlucagonAmino Acid Derived Hormones

– serotonin

– adrenaline

Protein FunctionsAntibodies & Immune System

– impaired immune system with protein deficiency

Fluid Balance– albumin– edema

Protein FunctionsAcid-Base Balance

– buffer– acidosis & alkalosis

Energy & Glucose– Unlike fats, amino acids can be converted into

glucose (required for CNS/brain function) starvation low carbohydrate diets

– body cannibalizes body proteins to make glucose

Protein and NutritionDaily protein needs

– Quantity of protein– Quality of protein

Protein Quality– How well a protein meets the body’s

need for health, growth, etc… Digestibility Amino acid composition

– Essential Amino Acids composition

Protein QualityMeasures of protein qualityBiological Value (BV)

– Measures body retention of food protein– BV=100 => 100% of food protein retained

Protein Efficiency Ratio (PER)– Measures ability of protein to support growth – g growth/g protein fed– PER=3 => 3g growth per g or protein fed

Protein Quality: BV

0102030405060708090100

Egg

Milk

Beef

Soy

Peas

Rice

Wheat

Lentils

Protein Quality: PER

0

0.5

1

1.5

2

2.5

3

3.5

4

Egg

Milk

Beef

Soy

Peas

Rice

Wheat

Lentils

Protein QualityVegetarian Diets

– Is there a protein problem? Plant proteins are “Incomplete proteins”Complementary Proteins

– Example: Mexican Food Tortilla: low lysine, hi methionine Beans: low in methionine, hi lysine

Tortillas & Rice with Refried Beans

© 2002 Wadsworth Publishing / Thomson Learning™

Hummus (garbanzo beans) and Pita Bread (wheat)

© 2002 Wadsworth Publishing / Thomson Learning™

Peanut butter (legume) sandwich (wheat)© 2002 Wadsworth Publishing / Thomson Learning™

Vegetarian Diets:Why become a vegetarian?

Health benefitsEnvironmental concerns about meat based

dietsAnimal welfare/ethical considerationsEconomic reasonsWorld hunger issuesReligious beliefs

Vegetarian Diets:Potential Health Benefits

Obesity– % of obesity lower in vegetarian populations

Cardiovascular Disease– Risk of CHD 31% lower in vegetarian men and 20% lower in

vegetarian women– Lower LDL-C, lower HDL-C

Hypertension– 42% non-veg with hpt, 13% vegetarians

Also lower prevalence for– Diabetes– Cancer

Vegetarian Diets:Consumer Trends - 2000

2.5% of adult Americans are vegetarians– 4.8 million people– Slightly less than 1% are vegans

20-25% of adult Americans eat 4 or more meatless meals weekly

“What do vegetarians in the United States eat?”

Am J Clin Nutr. 78S:626-632 (2003)

Continuing Survey of Food Intake by Individual (CSFII): 1994-1996– >13,000 subjects

2 day food records

2.5% considered themselves as vegetarian– 36% of self-defined vegetarians actually

consumed no meat ~4% of total consumed no meat

“What do vegetarians in the United States eat?”

Characteristics of Self-defined Vegetarians

Vegetarians were thinner– BMI: 23 vs 26

Consumed more CHO– 57% vs 50%

Less fat and saturated fat– 27% vs 33% and 9% vs 11%

More vitamin A, carotene, vitamin E, vitamin C, folate, dietary fiber and less cholesterol

Vegetarian Diets: TypesNon-red meat vegetarian

– poultry, fish, dairy, eggs OKNutritional Benefits

– Less fat, saturated fat, cholesterolNutritional Concerns

– no special nutritional problems– May not be any better than typical US diet

may be high in fat, sat’d fat, salt cooking methods junk foods, convenience foods

Vegetarian Diets: TypesLacto-ovo vegetarian

– Milk & eggs OKNutritional Benefits

– Like non-meat vegetarians

Nutritional Concerns– No special nutritional problems– May be high in fats, sat’d fats

cheese & eggs

Vegetarian Diets: TypesStrict Vegetarian: Vegan

– no animal foodsNutritional Benefits

– Low fats, high fiber, plant-basedNutritional Concerns

– protein quality probably OK, quantity may be an issue

– calcium no dairy, plant sources (leafy greens, soy), fortified foods (soy, rice milk)

– iron no meat, plant sources (leafy greens), cereals

– vitamin B-12 probably OK, cereals & supplements

Protein DeficiencyProtein - Energy Malnutrition

– > 500 million children with PEM– 33,000 die per day with PEM

Two major forms of PEM–Kwashiorkor

–Marasmus

Protein DeficiencyKwashiorkor

– Ghana “the evil spirit that infects the first child when the second child is born”

Protein low, Calories OK Symptoms

– edema– enlarged fatty liver– light colored hair

low tyrosine/melanin

– skin lesions

Protein DeficiencyMarasmusBoth Protein and Calories

low– inadequate food intake

Symptoms– wasting of lean and fat tissue– weak, anemic, low metabolism– death due to secondary

infections

Protein Needs RDA = 0.8g Pro/kg BW

–Or ~ 15% of caloriesM = 55 gP/d F = 45 gP/dSafety factor accounts for:

– individual differences– varied protein quality– average requirement 0.5-0.6gP/kg

Typical Intake: 65 - 110 gP/d

Athlete’s Protein Needs ?Most sport nutritionists recommend

– 1.0 to 1.5 g protein/kg BW– RDA = 0.8 gP/kg BW

Example of athlete’s protein needs 175 lb = 80 kg athlete

– 80 kg x 1.5gP/kg = 120 g protein needed per day

So do athletes need to supplement their diets? Usually not.

3500 Cal/d x 15%Pro = 525 Cal Pro– 525 Cal P / 4 Cal/gPro =

131 g pro in normal diet

For maximal muscle gain: Adequate protein

– 1.2 – 1.5 gPRO/kg BW 175 lbs = 80kg = 96-120gP/day If 3000 Cal diet = 13-16% of Calories

Adequate energy, especially Carbs– 6-7g CHO/kg BW

175 lbs = 480 –560 g CHO If 3000 Cal diet = 64% - 75%

Proper cellular hormonal balance– Genetics– Weight training– Cheating (anabolic steroids, androstenedione (prohormone)

Documents

Proteins and Amino Acids in Nutrition Dr. David L. Gee FCSN 245 Basic Nutrition