Nutrients

Suqing Wang

Proteins and Amino Acids

Amino Acids

Proteins contain C, H, O, and Nitrogen

Common structure: Central C, with a H, amino

group (NH2), and an acid group (COOH), and a side

group

Proteins made up of about 20 different amino acids;

Proteins are sequences of amino acids

Unique Side Groups

Differ in size, shape, electrical charge

氨基酸 英文 氨基酸 英文 必需氨基酸异亮氨酸亮氨酸赖氨酸蛋氨酸苯丙氨酸苏氨酸色氨酸缬氨酸组氨酸 *

非必需氨基酸丙氨酸精氨酸

Isoleucine(Ile)Leucine(Leu)Lysine(Lys)Methionine(Met)Phenylalanine(Phe)Threonine(Thr)Tryptophan(Trp)Valine(Val)Histidine(His) Alanine(Ala)Arginine(Arg)

天门冬氨酸天门冬酰胺谷氨酸谷氨酰胺甘氨酸脯氨酸丝氨酸

条件必需氨基酸半胱氨酸酪氨酸

Aspartic acid(Asp)Asparagine(Asn)Glutamic acid(Glu)Glutamine(Gln)Glycine(Gly)Proline(Pro)Serine(Ser) Cysteine(Cys)Tyrosine(Tyr)

* 组氨酸为婴儿必需氨基酸，成人需要量可能较少。

摘自 Modern Nutrition in Health and Disease ，第 9 版，第 14 页， 1999年。

构成人体蛋白质的氨基酸

Nonessential Amino Acids:

--body can synthesize for itself

--food often deliver

--more than 1/2 of a.a. are nonessential

Essential Amino Acids:

--body cannot make

--there are nine

--must be supplied in foods

Conditionally Essential Amino Acids:

--an a.a. normally nonessential but must

be supplied in diet in special circumstances

Amino Acids Are the Building Blocks of Protein

Protein structure

Chain of amino acids

Sequence of amino acids determines shape

Shape of protein determines function

Denaturing protein structure

Disrupts function

Caused by heat, acid, oxidation, agitation

Functions of Body Protein

Structural and mechanical functions

Collagen

Keratin

Motor proteins

Enzymes

Catalyze reactions

Hormones

Regulate body processes

Functions of Body Protein Immune function

Antibodies attack bacteria and viruses

Fluid balance

Blood proteins attract fluid

Acid-base balance

Proteins act as buffers

Transport

Lipoproteins, other carrier molecules

Source of energy

4 kcal/gram

Protein Digestion

Mouth

crushed and moistened

Stomach

Proteins are denatured by hydrochloric acid

Pepsin begins digestion

Small intestine

Pancreatic and intestinal proteases and

petidases complete digestion

Absorption of Amino Acids

Into intestinal cells

Transported across cell membrane to surrounding

fluid where enter capillaries on way to liver

Dietary intake of enzymes

Undigested Protein

Protein Synthesis

Delivering the instructions

messenger RNA: out through nuclear membrane;

attaches to ribosome; presents list with sequence

of a.a.

Lining up the amino acids

transfer RNA collect a.a. from cell fluid and bring to

messenger; a.a. move into position in order;

complete protein strand released; messenger

degraded; transfer RNA return for more loads;

Sequencing Errors

genetic error or mistake in copying can alter

the a.a. sequence of protein

example: Sickle cell anemia

Nutrients and Gene Expression

cells regulate gene expression to make amount,

rate and type of protein needed;

all cells posses genes for making all protein

each type of cell only makes proteins it needs

Proteins in the Body Amino Acid Pool

Protein Turnover

Synthesis of Nonprotein Molecules

Protein excretion

Deamination of amino acids

Amino groups converted to urea for excretion

Nitrogen balance

Nitrogen intake vs. nitrogen output

Proteins in the DietRecommended protein intake

Adult RDA = 0.8 grams/kilogram body weight

Infant RDA = 2.2 grams/kilogram body weight

15% of kcal intake

Increased protein needs

Physical stress

Injury

Intense weight training

Protein in the diet

U.S. protein intake > protein needs

Proteins in the Diet

Protein quality

Complete proteins

supply all essential amino acids

animal proteins, soy proteins

Incomplete proteins

low in one or more essential amino acids

most plant proteins

Complementary proteins

2 incomplete proteins = complete protein

Evaluating Protein QualityEvaluating protein quality

Amino acid composition

Digestibility

Protein Digestibility-Corrected Amino Acid Score (PDCAAS)

Used to determine %DV

Protein and amino acid supplements

Generally not needed

Risks unknown

lysine/tryptophan

Label Examples:

protein (g) % DV

Western Family yogurt: 11 g

Blue Bunny yogurt 6 g 12%

Egg 6 g 10%

Milk 8 g

String cheese 8 g

Hillshire Farm Ham 10 g 21%

1/2 c. Refried beans 7 g

1/2 c. navy beans 5 g

2 oz tuna 13 g

GrainsBarley, Bulgar, Cornmeal, Oats, Pasta, Rice, Whole-

grain breads

LegumesDried beans, Dried lentils, Dried peas, Peanuts, Soy

products

Seeds and NutsCashews, Nut butters, Other nuts, Sesame seeds, Sunflower seeds, Walnuts

VegetablesBroccoli, Leafy greens, Other vegetables

Complementary Protein Complementary Protein CombinationsCombinations

Mutual Supplementation

Ile Lys Met Trp

Legumes yes yes no no

Grains no no yes yes

Together yes yes yes yes

Health Effects of Protein

* Heart Disease

* homocysteine

* Cancer

* Osteoporosis

* calcium excretion rises as protein intake increases

* Weight Control

* Kidney Disease

* high protein intake increases work of kidneys

The Human Body: From Food to Fuel

Digestion and Absorption

The Gastrointestinal Tract Organization

Mouth anus

Accessory organs

Salivary glands, liver, pancreas, gallbladder

Functions

Ingestion

Transport

Secretion

Digestion

Absorption

Elimination

Overview of Digestion

Physical movement

Peristalsis

Segmentation

Chemical breakdown

Enzymes

Other secretions

Assisting Organs

Salivary glandsMoisten foodSupply enzymes

LiverProduces bileEnterohepatic circulation

GallbladderStores and secretes bile

PancreasSecretes bicarbonateSecretes enzymes

Digestion and AbsorptionMouth

Enzymes

Salivary amylase acts on starch

Lingual lipase acts on fat

Saliva

Moistens food for swallowing

Epiglottis; Dysphagia

Esophagus

Transports food to stomach

Esophageal sphincter

Stomach

Hydrochloric acid

Prepares protein for digestion

Activates enzymes

Pepsin

Begins protein digestion

Gastric lipase

Some fat digestion

Gastrin (hormone)

Stimulates gastric secretion and movement

Small intestine

Sections of small intestine

Duodenum, jejunum, ileum

Digestion

Bicarbonate neutralizes stomach acid

Pancreatic & intestinal enzymes

Carbohydrates

Fat

Protein

Small intestine

Absorption

Folds, villi, microvilli expand absorptive surface

Most nutrients absorbed here

Fat-soluble nutrients go into lymph

Other nutrients into blood

Large Intestine

Digestion

Nutrient digestion already

complete

Some digestion of fiber by

bacteria

Absorption

Water

Sodium, potassium, chloride

Vitamin K (produced by bacteria)

Elimination

Circulation of Nutrients

Vascular system

Lymphatic system

Excretion and elimination

Signaling Systems: Command, Control, Defense

Nervous system

Regulates GI activity

Local system of nerves

Central nervous system

Hormonal system

Increases or decreases GI activity

Immune system

Identifies and attacks foreign invaders

Nutrition and GI DisordersConstipation

Hard, dry, infrequent stoolsReduced by high fiber, fluid intake,

exerciseDiarrhea

Loose, watery, frequent stoolsSymptom of diseases/infectionsCan cause dehydration

DiverticulosisPouches along colonHigh fiber diet reduces formation

Gastroesophageal Reflux Disease (GERD)

Reduced by smaller meals, less fat

Irritable Bowel Syndrome (IBS)

Colon cancer

Antioxidants may reduce risk

Gas

Ulcers

Bacterial cause; helicobacter pylori

Functional dyspepsia

Carbohydrates

Sugars, Starches, Fibers

Major food sources: plants

Formed during

photosynthesis

Photo © PhotoDisc

PhotosynthesisPhotosynthesis

Simple Sugars:Mono and Disaccharides

Monosaccharides – single sugar unitGlucose

Found in fruits, vegetables, honey “blood sugar” – used for energy

Fructose “fruit sugar” Found in fruits, honey, corn syrup

Galactose Found as part of lactose in milk

Disaccharides – two linked sugar units

Sucrose: glucose + fructose

“table sugar”

Made from sugar cane and sugar

beets

Lactose: glucose + galactose

“milk sugar”

Found in milk and dairy products

Maltose: glucose + glucose

Found in germinating cereal grains

Product of starch breakdown

Complex Carbohydrates

Chains of more than two sugar molecules

Oligosaccharides

contain 3-10 sugar molecules

Polysaccharides

contain 100’s or 1000’s of monosaccharide units

starch-digestible

fiber-indigestible

Starch

Long chains of glucose units

Amylose – straight chains

Amylopectin – branched chains;

Resistant starch-not digested

Found in grains, vegetables, legumes

Glycogen

Highly branched chains of glucose units

Body’s storage form of carbohydrate

Dietary Fiber

Indigestible chains of monosaccharides

Oligosaccharides: short chains (3-10)

Non-starch polysaccharides: long chains

Cellulose, hemicellulose, pectins, gums, mucilages

Other: Lignins, cutins, waxes

Found in fruits, vegetables,grains, legumes

FiberOligosaccharides

dried beans, peas, lentils

rafinose (gal-glu-fru)

stachyose (gal-gal-gal-fru)

metabolized by intestinal bacteria

gaseous effects

Cellulose

makes walls of cells strong and rigid

Hemicelluloses

mixed with cellulose in cell walls

outer bran layer

Pectins

gel forming; in fruit

Gums and Mucilages

thick, gel-forming

used by food industry to thicken, stabilize,

Lignins

not a carb; indigestible substances that make up

woody parts of veg; and fruit seeds

Type of Fiber Major Food Sources Action in Body

Soluble FiberGums, pectins, Fruits (apples, citrus), * Delay GI transit.some hemicell, oats, barley, legumes * Delay glucosemucilages; absorption. *Lower

blood cholesterol.Insoluble FiberCellulose, many wheat bran, corn bran * Accelerate GIhemicelluloses, whole grain breads transit. *Increaselignins & cereals, vegetables fecal weight.

*Slow starch hydro- lysis. *Delay

glucose absorption.

Carbohydrate Digestion and Absorption

Mouth

Salivary amylase begins digestion of starch

Small intestine

Pancreatic amylase completes starch digestion

Brush border enzymes digest disaccharides

End products of carbohydrate digestion

Glucose, fructose, galactose

Absorbed into bloodstream

Fibers are not digested, excreted in feces

Functions of Carbohydrates

Energy source

Glucose is the body’s main fuel

Adequate glucose spares protein

Adequate glucose prevents ketosis

Allows for complete fat breakdown

Excess glucose is stored as glycogen

Stored in liver and muscle

DiabetesDiabetes Mellitus

Persistent high blood glucose levels

Complications of high BG

Type 1: lack of insulin production

Treat with insulin

Type 2: cells are resistant to insulin

Treat with diet and exercise

May treat with oral medications

May treat with insulin

Risk factors for type 2 diabetes

•Age

•Ethnicity

•Obesity

•Hx of Gestational DM

•Family history

•Lack of exercise

Metabolic Syndrome

Cluster of risk factors for heart disease associated with

insulin resistance

Hyperglycemia

High Blood Pressure

High Blood levels of insulin

High cholesterol levels

Carbohydrates in Your Diet

Recommended carbohydrate intake

55-60% of kilocalories

Daily Value (for 2,000 kcal) = 300 grams

Dietary Guidelines

Moderate sugar intake

Variety of grains, fruits, vegetables

Fiber intake of 25 grams/day

Increasing complex carbohydrate

intake

Grains,

especially whole grains

Legumes

Vegetables

Reducing sugar intake

Use less added sugar

Limit soft drinks, sugary cereals,

candy

Choose fresh fruits or those canned

in water or juice

Artificial Sweeteners

Minimal or zero kcal

Many times sweeter than sugar

Non-cariogenic (don’t promote tooth decay)

Current products --New Products

Saccharin * Neotame

Aspartame * D-tagatose

Acesulfame * Alitame

Sucralose

Sugar alcohols

~2 kcal/gram

Non-cariogenic

Carbohydrates and HealthHigh sugar intake

Low nutrient content

Contributes to tooth decay

If excess kcal, contributes to obesity

High fiber intake

Better control of blood glucose

Possible reduced cancer risk

Reduced risk of heart disease

Healthier gastrointestinal functioning

Lactose Intolerance

Lactose in milk and other dairy foods

Lactase enzyme

Symptoms

Native American; African American; Chinese; Thais

Alternative foods

Compared to a milk allergy

“ Net Carb” “Low Carb” “Impact Carb”

Total Carb

calculated by subtraction of the sum of crude protein,

total fat, moisture, and ash from the total weight of

the food

Subtract fiber g from total carb g if fiber > 5 g

Count 1/2 of sugar alcohol g as carb

But often subtract all sugar alcohol

Glycerin= glycerol; include in total carb g and sugar

alcohol g if stmt about sugars

The Lipids: Triglycerides, Phospholipids and Sterols

Fatty Acids

The Length of the Carbon Chain

long-chain, medium-chain, short-chain

The Degree of Unsaturation

saturated, unsaturated, monounsaturated,

polyunsaturated

The Location of Double Bonds

omega-3 fatty acid, omega-6 fatty acid

Fatty Acids are Key Building Blocks

Saturated Fatty Acid

All single bonds between carbons

Monounsaturated Fatty Acid(MUFA)

One carbon-carbon double bond

Polyunsaturated Fatty Acid(PUFA)

More than one carbon-carbon double bond

Location of Double Bonds

PUFA are identified by position of the double bond

nearest the methyl end (CH3) of the carbon chain;

this is described as a omega number;

If PUFA has first double bond 3 carbons away from

the methyl end=omega 3 FA

6 carbons from methyl end=omega 6 FA

Degree of Unsaturation Firmness

saturated vs. unsaturated

Stability

oxidation, antioxidants

Hydrogenation

advantages, disadvantages

Trans-Fatty Acids

from hydrogenation

Essential Fatty Acids (EFA)Omega-3:

Eicosopentaenoic acid (EPA)

Docosahexaenoic acid (DHA)

Alpha-linolenic acid (ALA)

flaxseed--most, canola (rapeseed), soybean,

walnut, wheat germ

body can make some EPA and DHA from ALA

Omega-6

corn, safflower, cottonseed, sesame, sunflower

Linoleic acid

FISH

Omega-3 Fatty AcidsAssociated with:

anti-inflammatory, antithrombotic, antiarrhythmic,

hypolipidemic, vasodilatory properties

Inflammatory conditions

Ulcerative colitis, Crohn’s

Cardiovascular disease

Type 2 diabetes * Mental function

Renal disease * Growth and

development

Essential Fatty Acid DeficiencyClassical symptoms include:

growth retardation, reproductive failure, skin lesions,

kidney and liver disorders, subtle neurological and

visual problems

People with chronic intestinal diseases

Depression--omega-3

?inadequate intake alters brain activity or depression

alters fatty acid metabolism?

Attention Deficit Hyperactivity Disorder

lower levels of omega-3--more behavioral problems

Eicosanoids: made from EFA

--derivatives of 20-carbon fatty acids;

--affect cells where they are made;

--have different effects in different cells

--cause muscles to contract and muscles to relax;

--help regulate blood pressure, blood clot formation,

blood lipids, and immune response;

--participate in immune response to injury and

infection, producing fever, inflammation, and pain;

--include:prostaglandins, thromboxanes, leukotrienes

Triglycerides

Structure

Glycerol + 3 fatty acids

Functions

Energy source

9 kcals per gram

Form of stored energy in adipose tissue

Insulation and protection

Carrier of fat-soluble vitamins

Sensory properties in food

Triglycerides

Food sources

fats and oils

butter, margarine, meat, baked goods, snack

foods, salad dressings, dairy products, nuts,

seeds

Sources of omega-3 fatty acids

Soybean, canola, walnut, flaxseed oils

Salmon, tuna, mackerel

Sources of omega-6 fatty acids

Vegetable oils

Fatty Acids in Common Food Fatty Acids in Common Food FatsFats

Phospholipids

Structure

Glycerol + 2 fatty acids + phosphate

group

Functions

Component of cell membranes

Lipid transport as part of lipoproteins

Emulsifiers

Phosphatidylcholine

Food sources

Egg yolks, liver, soybeans, peanuts

Sterols: Cholesterol

Functions

Component of cell membranes

Precursor to other substances

Sterol hormones

Vitamin D

Bile acids

Synthesis

Made mainly in the liver

Food sources

Found only in animal foods

Lipid Digestion

In the Mouth

hard fats begin to melt; lingual lipase

In the Stomach

gastric lipase--SCFA

In the Small Intestine

release of CCK; bile-emulsifier; fat drawn into

surrounding watery fluids; intestinal lipases;

remove each TG fatty acid; leave glycerol;

Bile Routes

reabsorbed or trapped by dietary fiber

Olestra

Sucrose + fatty acids

Indigestible – provides zero

kcals

Reduces absorption of fat-

soluble vitamins

So many fatty acid chains are

crowded around the core, the

digestive enzymes cannot find a

breaking point

Orlistat (Xenical)

* binds to active site of GI lipase and

blocks its activity; thus, lipase can’t

break TG down to component parts;

TG remains undigested and

unabsorbed

Health Effects of Lipids

Risks from Saturated Fats

saturated fats raise LDL cholesterol

LDL raises the risk of heart disease

Risks from trans-Fats

raise LDL cholesterol and lower HDL chol.

Cardiovascular disease (CVD)

all diseases of the heart and blood vessels

Coronary heart disease (CHD)

arteries around heart are blocked, cause

damage

FatBenefits from Omega-3 Polyunsaturated

Fats/Cancer/Obesity/Fat restriction

Recommended Intakes of Fat:

Total Fat 30% of total kcals

Saturated fat less than 10% of total kcals

Cholesterol less than 300 mg

Reduce Total Fat, Saturated Fat, trans-fat intake

from foods

Reduce Cholesterol Intake

Healthy Food Choices

Balance Omega-3 and Omega-6 Intakes

Select Lean Meats and Nonfat milks

Eat Plenty of Vegetables, Fruits, Grains

Use Fats and Oils Sparingly

Look for Invisible Fat

Choose Wisely

Read Food Labels

Lipid Absorption

Glycerol, SCFA, MCFA diffuse into intestinal cells;

absorbed directly into blood stream;

Monoglycerides and LCFA merge into micelles;

into intestinal cells; reassemble into TG;

new TG packed into chylomicrons; into lymph

system; point of entry to bloodstream at thoracic

duct near the heart; to rest of body;

Lipid Transport

Lipoproteins: clusters of lipids associated with proteins

that serve as transport vehicles for lipids in the lymph

and blood;

4 main types of lipoproteins

1. Chylomicrons

2. VLDL

3. LDL

4. HDL

Lipoproteins1. Chylomicrons

transport diet-derived lipids (mostly TG) from

intestine to rest of the body;

cells from all over the body remove lipids as the

chylomicrons pass by; get smaller; protein

remnants left; go to liver;

2. VLDL (Very Low Density Lipoprotein)

liver site of lipid synthesis; lipid packaged with

proteins shipped to other parts of the body; cells

remove TG; become more dense;

3. LDL (Low Density Lipoproteins)

derived from VLDL; circulate throughout body; content

available to cells to build new membranes, make

hormones, or store;

LDL receptors on liver cells remove LDL from circulation;

4. HDL (High Density Lipoproteins)

carries cholesterol and other lipids from the cells back to

the liver for recycling or disposal

mostly protein;

Lipid MetabolismStoring Fat as Fat

Fat cells of adipose tissue take up and store fat;

LPL on adipose cell surface captures circulating

TG after meals;

Making Fat from Carb or Protein

FA can be made from carb or pro components;

requires energy

Making Fat from Fat

little energy to do this;

Health Implications

LDL (lousy):linked to heart disease

HDL (happy): protective from heart disease

Factors that improve LDL-HDL ratio:

weight control

MUFA/PUFA vs. SFA

Soluble fiber

Antioxidants

Physical activity

Moderate alcohol consumption

Heart Disease Blood Lipid Profile:

Total Cholesterol: Desirable: < 200 mg/dl

(borderline:200-239 and high: >240)

LDL Cholesterol: Optimal: < 100 mg/dl

(near optimal: 100-129; borderline high:130-159

High: 160-189; Very High: >190)

HDL Cholesterol: Risk factor: <40 mg/dl

40-59: better; >60: protective

Triglyceride: Desirable: < 150 mg/dl;

(B: 150-199; high: 200-499; very high: >500)