chapter01-carbohydrates lipids proteins

Copyright © 2015 Wolters Kluwer Health | Lippincott Williams & Wilkins

Chapter 1Carbohydrates, Lipids, and

Proteins

Objectives• Distinguish between different types of carbohydrates• Identify two major fiber types and their roles in health• Discuss physiologic responses to different dietary carbohydrates

in the development of Type II diabetes and obesity • Identify the amount and distribution of carbohydrate energy

storage in the average male• Summarize the role of carbohydrate in energy metabolism• Describe the dynamics of carbohydrate and fat metabolism along

the physical activity intensity/duration continuum• Compare/contrast the speed of energy transfer of carbohydrates

and fats• Discuss how diet affects muscle/liver glycogen and endurance

performance• Describe food sources and health implications of different types

of fatty acids• Describe major blood lipoproteins and role in CHD development• Understand prudent recommendations for dietary fat and

cholesterol intake

Objectives, con’t.• Identify the amount and distribution of fat energy storage in the

average female• List functions of fat in the body• Discuss training adaptations in the use of carbohydrates and fats• Distinguish between essential and nonessential amino acids• Discuss the health and performance advantages and possible

limitations of a vegetarian diet• Describe the dynamics of protein metabolism along the physical

activity intensity/duration continuum• Provide a rationale for increasing dietary protein intake above

the RDA for individuals engaged in strenuous endurance and/or resistance training

• Describe the use of protein in energy metabolism and the Cori cycle in gluconeogenesis

Nutrients for Health and PerformanceMacronutrients (containing energy)Nutrient Atwater

Factor (Kcal·g-1)

Acceptable Macronutrient

Distribution RangeCarbohydrates Main Energy Food;

Most Efficient Energy Substrate

4 45-65%

Fats An Important and Most Abundant Energy Source

9 20-35%

Protein Energy Source, Tissue Builder, Enzymes and Metabolic Regulators

4 10-35%

Micronutrients (metabolic regulators/coenzymes)Vitamins Organic Regulators NAMinerals Inorganic Regulators NAWater Solvent NA

Carbohydrates• Three Classifications of Carbohydrates

– Monosaccharides• Basic unit of carbohydrates

– Oligosaccharides• 2-10 monosaccharides bonded chemically

– Polysaccharides• 3 to thousands of sugar molecule linkages

Photosynthesis – An Endergonic Process

http://www.uic.edu/classes/bios/bios100/f05pm/lect08a.htm

Photosynthesis is the conversion of solar energy to chemical energy in plants.The following net reaction: 6H2O + 6CO2 → 6O2+ C6H12O6 occurs in the chloroplasts, analogous to mitochondria in animals.These reactions occur in the thylakoid membrane and the stroma. The thykaloid membrane is analogous to the mitochondrial inter-membrane that is highly folded upon itself to create a large surface area of grana discs (analogous to the mitochondrial cristae).The stroma is the “cytoplasm” of the chloroplast.

Site of light-dependent (light)

reactions

Site of light-independent (dark)

reactions










2H2O

P 680 Photosystem IIon thykaloid membranes

Electron Acceptor

4e-

4e-

P 700 Photosystem Ion thykaloid membranes

4H+ + O2

Electron Transport Chain

4e-

Electron Acceptor

4e-

Electron Transport Chain

H+

ATP

NADP+ NADPH H+

ATP formation by chemi-osmotic proton

gradient

Light-dependent reactions

Photon

Photon









http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb2/part1/dark.htm

Calvin-Benson CycleCO2

ADP

ATP

ADPATP

NADPH H+

NADP+

Ribulose bisphosphate carboxylase

Ribulose 1,5-bisphosphate

3-Phosphoglycerate1,3-bisphosphoglycerate

Glyceraldehyde-3-Phosphate

Dehydrogenase

Aldolase

Ribulose 5-phosphate Fructose-1,6-bisPhosphate

Fructose-6-Phosphate

Fructose 1,6 bisphosphatase

H2O

Glucose

PhosphoglycerateKinase

G3PDHAP Triose

Isomerase

H2O+N2+CO2

CHO Fats

Protein

O2

CHOFats

Protein

Vegans

Solar Energy links Photosynthesis and Energy Metabolism

ATP

CO2

CO2

ATP

Monosaccharides (C6H12O6)– Glucose or dextrose (blood sugar)

– Fructose (fruit sugar)

Monosaccharides– Galactose (milk sugar)

Oligosaccharides• The major oligosaccharide is the dissaccharide or double

sugar– Maltose= Glucose + Glucose

– Lactose= Galactose + Glucose

– Sucrose= Glucose + Fructose

Glu Glu

GluGal

Glu Fruc

Polysaccharides• Plant polysaccharides

– Starch is the storage form of carbohydrates in plants• Amylose (20-30%)

• Resistant Starch

• Amylopectin (70-80%) similar to glycogen, less branching

– Fiber occurs exclusively in plants• Cellulose

http://www.sciencedirect.com/science/article/pii/S0733521003001139







Daily Recommended Intake of Fiber• Under 50

– 38 g for men– 25 g for women

• Over 50– 30 g for men– 21 g for women

• Ratio of 3:1 for water-insoluble to soluble fiber

Cholesterol in foods• Cholesterol is a sterol [not a fat] found only in animal products

that may be manufactured in the liver from carbohydrates, fatty acids, and protein.

• Cholesterol is not an essential nutrient, i.e., necessary in the diet• Isopentyl Pyrophosopate is a precursor for Vitamins A, E, and K • Cholesterol is a precursor for Vitamin D and mineralocortocoid,

glucocorticoid, and sex hormones.

http://sph.bu.edu/otlt/MPH-Modules/PH/PH709_A_Cellular_World/PH709_BuildingBlocks4.html

Acetyl CoA + Acetyl CoA → Acetoacetyl CoA + CoAAcetoacetyl CoA + Acetyl CoA + H2O → 3-hydroxy-3-methylglutaryl CoA + CoA + H+

3-hydroxy-3-methylglutaryl CoA + 2NADPH + 2H+ → Mevalonate + CoA + 2 NADP+

Hydroxymethylglutaryl CoA reductase is the rate-limiting enzyme in de novo cholesterol biosynthesis

Mevalonate → Isopentyl Pyrophosphate → Geranyl Pyrophosphate → Farnesyl Pyrophosphate → Squalene → Cholesterol










Glycogen Synthesis

ATPADP

Hexokinase

Glucose

Glucose-6-Phosphate

Phospho-glucomutase

Glucose-1-Phosphate

Glucose-1-phosphate uridylytransferase

http://themedicalbiochemistrypage.org/glycogen.php#synthesis

Glycogen Synthesis

UDP-Glucose

Uridine Triphosphate

Pyrophosphate

Next Slide





Glycogen


Glycogen+1 Glycosyl unitα 1→4 bonds

Glycogen Synthesis, con’t.

Glycogen Synthase

UDP-Glucose

UDP

α 1→6 bondnext slide





H

H

α 1→ 4 bonds

α 1→ 6 bonds

α 1→ 6 bonds

Glycogen Structure

Glycogenin, an enzyme that accepts the first glucosyl on a tyrosine residue on each of its two dimers, provides an “anchor” for de novo glycogen synthesis

http://commons.wikimedia.org/wiki/File:Glycosyl(n)glycogenin.svg Glycogenin

tyr

http://commons.wikimedia.org/wiki/File:Glycosyl(n)glycogenin.svg






Daily Recommendation of Carbohydrates• Sedentary 70kg person

– 300g or 40-50% of total calories• Physically active person

– 400-600g or 60% of total calories• Athlete

– 70% of total calories (8-10 g·kg body mass-1)• Maximum capacity for glycogen storage is ~15g·kg body

mass-1

~79.5%

~19.9%

~0.6%

Role of Carbohydrates• Energy source

– Energy is derived from the breakdown of blood-borne glucose

– Muscle glycogen powers various forms of biologic work including muscle contraction

• Protein sparer– Adequate carbohydrate intake helps to preserve tissue

protein• Metabolic primer

– The depletion of glycogen causes fat mobilization to exceed fat oxidation

– Can lead to ketosis• Fuel for the central nervous system

– The brain almost exclusively uses blood glucose as its fuel source

– Hypoglycemia is the reduction of blood glucose to<45 mg·dl-1 (2.5 mmol·l-1)

Metabolism and Function • Digestion

– Enzymatic activity

• Absorption (primarily in the small intestine)– Diffusion– Facilitated

diffusion– Active

transport

AbsorptionOsmosis: net movement of water across a selectively permeable membrane dividing solutions of different solute concentrations (from Low [C] to High [C])Diffusion: Random, uniform and continuous movement across a selectively permeable membrane from High [C] to Low [C]Facilitated Diffusion: Movement across a selectively permeable membrane from High [C] to Low [C] by a carrier moleculeActive Transport: Energy requiring movement from Low [C] to High [C]

Carbohydrate Dynamics in Exercise• Intensity and duration determine the fuel mixture during

exercise– High-intensity exercise

• One hour of high-intensity exercise decreases liver glycogen by 55%

• Two hours almost depletes the liver and muscle glycogen

– Moderate and prolonged exercise• During low-intensity exercise fat serves as the

main energy substrate

3.5 8.5 13.5 18.5 23.5 28.5 33.5 38.5 43.5 48.5 53.50.60

0.70

0.80

0.90

1.00

1.10

1.20

1.30

1.40

Substrate utilization during incremental cycle exercise to exhaustion (32.5 W∙min-1

increments)

VO2 (ml∙kg-1∙min-1)

Non

-pro

tein

RER

(VC

O2÷

VO2)

VO2 (X) %VO2max RER (Y) %CHO %Fat

Thermal Equivalent of oxygen for non‑protein RER including % carbohydrate (CHO) and fatNon Protein RER Kcal∙liter O2

-1 %CHO %Fat0.707 4.686 0 1000.71 4.69 1.1 98.90.72 4.702 4.76 95.20.73 4.714 8.4 91.60.74 4.727 12 880.75 4.739 15.6 84.40.76 4.751 19.2 80.80.77 4.764 22.8 77.20.78 4.776 26.3 73.70.79 4.788 29.9 70.10.80 4.801 33.4 66.60.81 4.813 36.9 63.10.82 4.825 40.3 59.70.83 4.836 43.8 56.20.84 4.85 47.2 52.80.85 4.862 50.7 49.30.86 4.875 54.1 45.90.87 4.887 57.5 42.50.88 4.899 60.8 39.20.89 4.911 64.2 35.80.90 4.924 67.5 32.50.91 4.936 70.8 29.20.92 4.948 74.1 25.90.93 4.961 77.4 22.60.94 4.973 80.7 19.30.95 4.985 84 160.96 4.998 87.2 12.80.97 5.01 90.4 9.60.98 5.022 93.6 6.40.99 5.035 96.8 3.21.00 5.047 100 0

2 23.84 47 0.79 29.9 70.13 30.61 60 0.92 74.1 25.94 38.59 75 1.00 100 05 51.15 100 1.29 100 0

1 10.65 21 0.76 19.2 80.8

CHO>Fat

~50%/50%CHO/Fat

Fat>CHO

Dynamics of Nutrient Metabolism

Exercise Time

CHO LoadedCHO Depleted

CHO Loaded

CHO Loaded

CHO Loaded

CHO Depleted

CHO Depleted

CHO Depleted

Plasma [glucose] decreases in the glycogen depleted state

Plasma [free fatty acids] increase in the glycogendepleted state

Increase in [ketones] (e.g., β-hydroxybutyrate) in the glycogen depleted state reflects greater use of ketogenic amino acids and fatty acids for energy metabolism

Ability to maintain intensity of exercise is adversely affected in the glycogen depleted state

Fatigue• Fatigue occurs when exercise continues to the point that

compromises liver and muscle glycogen.• Fatigue is commonly referred to as “hitting the wall.” • The rate of use of CHO by exercising muscle exceeds

hepatic glucose output by glycolysis or gluconeogenesis.• Fatigue is a complex phenomenon that is not completely

understood but likely includes central/peripheral nervous and muscular perturbations in addition to energy substrate availability.

Key points about carbohydrates • Carbohydrates consist of hydrogen, oxygen and carbon in a 2:1:1

respective ratio, e.g., glucose C6H12O6• Carbohydrates are produced by plants as part of photosynthesis

and exist as monosaccharides (glucose, fructose, galactose); disaccharides (sucrose, maltose, lactose); and polymers (amylose, amylopectin [plants], glycogen [animals]).

• Glycogen is a polymer of glucose (glucosyl) units in linear (α 1-4) and branch(α 1-6) chains and is found in muscle (~80%) and liver (~20%).

• Glycolysis is the progressive “pruning” of glucosyl units from the non-reducing end of the polymer for ATP synthesis (muscle) or for blood glucose (liver). Glycogen phosphorylase, the enzyme mobilizing a glucosyl unit from glycogen to undergo glycolysis, is stimulated by the catecholamines epinepherine and norepinephrine and the hormone glucagon. It is inhibited by the hormone insulin.

• Gluconeogenesis is the formation of glucose by the liver from glucogenic amino acids, glycerol, lactate, and pyruvate.

• The acceptable macronutrient distribution range for carbohydrates is 45-65% of total calories.

Key points about carbohydrates, con’t. • Carbohydrates is a major energy substrate, spares protein for

structure and regulatory purposes, primes fat oxidation, and is the preferred and only substrate for the CNS and red blood cells, respectively.

• Carbohydrate is the only energy substrate for anaerobic glycolysis and is the preferred fuel for prolonged, high intensity aerobic exercise.

• Adequate muscle [glycogen] is a prerequisite for optimal high intensity aerobic exercise and requires adequate intake of dietary carbohydrate (60-70% of total calories, 8-10 g·kg body mass-1).

• The price of glycogen depletion is a decrease in exercise intensity dependent on training adaptations to mobilize and oxidize fat.

Lipids• Lipids are synthesized by plants and animals• There are three groups of lipids

– Simple– Compound– Derived

Simple Lipids• Simple lipids consist primarily of triacylglycerols (TAG),

a.k.a., triglycerides– TAG is the major storage form of fat in adipocytes.– TAG contains one glycerol and three fatty acid chains– The longer the fatty acid chain in the TAG, the less

water-soluble the molecule.

Fatty Acids• Saturated fatty acids

– When the carbon binds to the maximum number of hydrogens

– Occur primarily in animal products• Beef, lamb, pork, egg yolk

• Unsaturated fatty acids have at least one double bond betwwen adjacent carbons. As a result, unsaturated fatty acids – Monounsaturated contains one double bond – Polyunsaturated contain two or more double bonds

• Linolenic acid is an essential fatty acid

Types of fatty acids [R= (CH3)-CH2-CH2…]C-C

bonds are all single

One double C=C

bond; the others are

single

H functional groups are

on the same side of the C=C bond -

liquid

H functional groups are on opposite sides of the C=C bond -

solid

Multiple (more

than one) C=C

bonds

Double C=C bond

between the 3rd and 4th C from the end (ω-3 or n-3)

Glycerol Fatty Acid Fatty AcidGlycerol

3 H2O

H H-

Triglycerides (a.k.a., triacylglycerol): an ester of glycerol (3 carbon alcohol) and three fatty acids

H H-

H H-

Linoleic Acid ω-6 (C18 2C Δ9,12) Linolenic Acid ω-3 (C18 3C Δ9,12,15)

CH2

CH2 CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH3

CH2CH2CH2

CH2CH2CH2

CHHC

HC

HC

HC

HC

C

Essential Fatty Acids

Composition of Fatty Acids

Fat content in selected fats and oils

TAG Formation

Triacylglycerol FormationO H H H H H H H H H H H H H H|| | | | | | | | | | | | | | |

CoA-S- C - C- C C- C- C- C- C- C- C- C- C- C- C- C- CH3

| | | | | | | | | | | | | | |H H H H H H H H H H H H H H H

O H H H H H H H H H H H H H H|| | | | | | | | | | | | | | |

-C - C- C C- C- C- C- C- C- C- C- C- C- C- C- CH3


CoA-SH

Fatty Acyl CoA Ester

Glycerol-3-Phosphate

Lysophosphatidic acid

Glycerol-3-phosphate acyltransferase

Acylglycerophosphateacyltransferase




Fatty Acyl CoA EsterCoA-SH



| | | | | | | | | | | | | | |H H H H H H H H H H H H H H HO H H H H H H H H H H H H H H|| | | | | | | | | | | | | | |

-C - C- C -C- C- C- C- C- C- C- C- C- C- C- C- CH3

| | | | | | | | | | | | | | |H H H H H H H H H H H H H H HO||

O- P- O-

|O-

Phosphatidic acid





| | | | | | | | | | | | | | |H H H H H H H H H H H H H H H O

||O- P- O-

|O-

OH

Phosphatidic Acid Phosphohydrolase

DiacylglycerolNext slide

TAG Formation




CoA-SH






OH

Diacylglycerol






Fatty Acyl CoA Ester

Diacylglycerol acyltransferase

Triacylglycerol




TAG Catabolism

Triacylglycerol Catabolism• Lipolysis of triacylglycerol occurs through

– hormone-mediated (epinephrine) action of hormone sensitive lipase in adipocytes (free fatty acids bound to albumin)

– capillary membrane-bound lipoprotein lipase (lipolysis of triacylglycerol in chylomicrons and blood lipoproteins) with uptake and reesterification of free fatty acids and triacylglycerol synthesis by adjacent tissue

• Lipolysis prominently occurs during – Low-moderate intensity exercise– Low CHO intake or energy intake restriction– Cold stress– Glycogen depletion (with concurrent decline in

performance)

Trans Fatty Acids• Result of partial hydrogenation of unsaturated fatty acids

creating monounsaturated fatty acids in the trans arrangement that are more closely packed (less steric hinderance) and therefore are semi-solid or solid at room temperature

• Nutrition Facts labeling requires listing trans fat in grams per serving

• Health concerns– Increases amount of low-density lipoprotein cholesterol

(LDL-C) similarly to naturally occurring saturated fatty acids

– Decreases amount of beneficial high-density lipoprotein cholesterol (HDL-C) unlike naturally occuring saturated fatty acids

Lipids in the DietA healthier American lifestyle would include:

-Less total fat in the diet

-Less saturated animal fat, more mono- and polyunsaturated fat

-More physical activity

Compound Lipids• Phospholipids have four main functions

– Interact with water and lipid to modulate fluid movement across cell membranes

– Maintain the structural integrity of the cell– Play important role in blood clotting– Provide structural integrity to the insulating sheath that

surrounds nerve fibers

Hydrophobic(inner)

Hydrophilic(outer)

Phosphate

Choline

Compound Lipids• Glycolipids

– Fatty acids bound with carbohydrates and nitrogen• Lipoproteins

– Packages produced in the small intestine and liver including• Protein• Phospholipids• Triacylglycerol• Cholesterol• Cholesterol-fatty acid esters

Blood Lymph Epithelial Cell Villi Small Intestinal Lumen

Absorption of Dietary Lipids

Lipoproteins• Four types

– Chylomicrons – transport Vitamins A, D, E, and K– High-density lipoprotein (HDL-C)– “good” cholesterol– Very low-density lipoprotein (VLDL-C)– transport TAGs

to muscle and adipose– Low-density lipoprotein (LDL-C) – “bad” cholesterol

Composition of chylomicrons and lipoproteins

http://www.nature.com/ng/journal/v40/n2/fig_tab/ng0208-129_F1.html

11

2 5

3

4

2

341

31

2

General Metabolic Pathways of Chylomicrons, HDL-C, and VLDL-C/IDC-C/LDL-C













Derived Lipids• Cholesterol

– Cholesterol is a sterol.– Cholesterol exists only in animal tissue.– Diets high in cholesterol can cause increased risk of

coronary heart disease and atherosclerosis.

http://www.heartsite.com/html/cad.html

Tunica AdventitiaTunica MediaTunica Intima

Normal concentrations of serum [lipids]Lipid Concentration

(mg∙dl-1)Conversion Factor → (∙)

or ← (÷)

Concentration (mmol∙l-1)

Comments

[Total Cholesterol]

110-200 0.0256 2.82-5.12 Lower is better

[HDL-Cholesterol]

40-59 0.0256 1.024-1.51 Higher is better

Calculated [LDL-Cholesterol]

50-99 0.0256 1.28-2.53 Lower is better, Calculated as [Total] - [HDL-C] - ([TG] ÷ 5)

[Triglycerides] 40-149 0.0113 0.45-1.68 Lower is betterCalculated [VLDL-Cholesterol]

8-30 0.0256 0.205-0.768 Lower is better, Calculated as ([TG] ÷ 5)

[Total Cholesterol] ÷ [HDL-Cholesterol]

4.4 NA NA Lower is better

National Cholesterol Education Guidelines: Fasting levels in mg∙dl-1

• Total cholesterol– Less than 200:

Desirable– 200-239: Borderline high– ≥ 240: High

• LDL-cholesterol– Less than 100:

Optimal– 100-129: Near Optimal– 130-159: Borderline high– 160-189: High– ≥ 190: Very high

• HDL-cholesterol- Less than 40: Low- ≥ 60 or above:

Protective

• Triglycerides- Less than 150:

Normal- 151-199: Borderline high- 200-499: High- ≥500: Very high

Daily Recommended Lipid Intake• A diet that contains 20% of total calories from lipids

– ≤ 10% (ideally, ≤ 7%) from saturated fats• Replace high fat foods with fruits, vegetables, whole

grains, fish, poultry, and lean meat• More plant foods, leaner choices of meat and dairy

products• More mono- and polyunsaturated (plant) fats in place of

saturated (animal) fats• Adequate intake of ω-3 and ω-6 polyunsaturated fatty

acids• Do not replace fats with refined carbohydrates• Reduce dietary cholesterol intake

Role of Lipids in the Body• Energy source and reserve

– Carries large quantities of energy per unit weight• Fat storage has played a prominent role in the the

evolution and survival of homo sapiens. – Transports and stores easily– Provides a ready source of energy– Protein sparer

• Protection of vital organs (Visceral)• Thermal insulation (Subcutaneous)

– Advantageous in cold water/weather and high impact sports– Disadvantageous in thermoregulation during hyperthermic

exercise• Vitamin carrier (Vitamins A,D,E,K) and hunger suppressor

Male= 80 kg · 0.15 = 12 kg adipose tissue= 12,000 g fat·9 kcal·g-1

= 108,000 kcal adipose fat + plasma and IM fat

Female= 56 kg · 0.25 = 14 kg adipose tissue= 14,000 g fat·9 kcal·g-1= 126,000 kcal adipose fat + plasma and IM fat

Potential fat energy in an 80 kg male with estimated 15% fat; 56 kg female with

estimated 25% fat

Fat Dynamics in Exercise• Light to moderate exercise

– Energy comes from fatty acids• Moderate intensity exercise

– Energy comes from equal amounts of carbohydrate and fat supply

• High intensity exercise– Carbohydrates, primarily muscle glycogen is the

source of energy

Effect of prolonged submaximal exercise (2.36 l·min-1) on Respiratory Quotient (RQ) and substrate utilization

RQ=Steady-state at the mitochondria100% Fat oxidation=0.7100% Carbohydrate oxidation=1.00> 0.7 - < 1.0 Fat/CHO mix

Declining steady-state RQ=explained by decreasing CHO utilization and increasing FFA utilization due to decreased insulin secretion and increased glucagon secretion.

~78%

~22%

~80%

~18%

Substrate use during steady-state cycle ergometer exercise at 25%, 65% and 85% of VO2max

Substrate 25% VO2max

65% VO2max

85% VO2max

Muscle Glycogen 1.5 37.8 58.7Muscle TAG 16.5 23.0 12.1Plasma [FFA] 70.1 27.0 14.6Plasma [Glucose] 11.9 12.2 14.6Total 100.0 100.0 100.0

6.3 15.4 21.0kcal·min-1

25% VO2max 65% VO2max 85% VO2max0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

Effect of exercise intensity on steady-state substrate utilization (VO2max~5 l·min-1);

Body Mass = 70 kgMuscle Glycogen Muscle Triacylglycerol Plasma [FFA]Plasma [Glucose]

Exercise Intensity

Perc

ent s

ubst

rate

util

izat

ion

Substrate use during prolonged steady-state cycle ergometer exercise

Declining availability of muscle glycogen, TAG and amino acids

Declining availability of plasma [glucose]

Increased lipolysis,mobilization and use of plasma [FFA]

Intensity Mass Rel VO2

Abs VO2

Steady State RER

Cal·liter O

2-1 Cal·min-1 %

CHO% Fat

Low - Walking 4 miles·hr-1

80 14.2 1.14 0.84 4.85 5.5 47.2 52.8

High - Running 6 miles·hr-1

80 35.7 2.85 0.94 4.97 14.2 80.7 19.3

Low - Walking 4 mph High - Running 6 mph0

102030405060708090

% Contribution of CHO and fats to energy metabolism in selected low-

and high-intensity exercise tasks %CHO %Fat

Exercise Training Intensity

% b

ased

on

stea

dy-s

tate

no

n-pr

otei

n RE

R

Low - Walking 4 mph High - Running 6 mph0

2

4

6

8

10

12

Calories·min-1 from catabolism of CHO and fats in selected low- and high-in-

tensity exercise tasksCal CHO CAL Fat

Exercise Training Intensity

Calo

ries·

min

-1

Fat oxidation in low- and high-intensity steady-state exercise. Rationale for weight loss.

Grams· liter O

2-1

CHO

Grams· liter O

2-1

Fat

Grams CHO

Grams Fat

Cal CHO

CAL Fat

0.537 0.28 0.611 0.319 2.4 2.9

0.964 0.108 2.75 0.308 11 2.8

The Myth of The Fat Burning Zone• Although it is correct that the percentage of energy from fat oxidation

increases as exercise intensity decreases, one must be cautious when interpreting exercise energy expenditure and substrate utilization data.

• If the goal of an athlete or individual is to oxidize as much fat and spare as much glycogen as possible, then it is important to determine the exercise intensity that elicits the appropriate metabolic response.

• However, if the goal is weight loss, which is important to many individuals today, then total energy expenditure is more important than whether fat or carbohydrate is the dominant substrate.

• Although low-intensity exercise results in a higher percentage of fat being oxidized for fuel, it also results in significantly fewer calories being expended.

• Training in the “fat burning zone” for weight loss is a myth. Fitness professionals should prescribe exercise intensity based on their client’s current fitness levels and goals. The best recommendation for most exercisers who want to achieve a healthy body weight and improve their fitness is to exercise at the highest intensity appropriate for their age, health, motivation, and current fitness level.

Effect of the trained state on substrate availabilityand utilization–Better “fat burner” with

concurrent conservation of glycogen

Greater (46% vs. 24%) post-training use of intramuscular TAG stores

Lower (38% vs. 58%) post-training rate of intramuscular glycolysis

Key points about lipids • Lipids, like carbohydrates, consist of hydrogen, oxygen and carbon,

but in a much higher hydrogen:oxygen ratio, e.g. stearic acid C18H35O2

• Simple lipids (a.k.a, triacylglycerol) consist of glycerol and three fatty acids. Compound lipids (a.k.a., phospholipids) consist of lipids combined with other compounds. Lipoproteins consist of protein, cholesterol, cholesterol-fatty acid esters, phospholipids, and triacylglycerol.

• Saturated fatty acids are fully saturated with hydrogens along the hydrocarbon chain, have single valent bonds between adjacent carbon atoms, come primarily from the animal kingdom, and are solids at room temperature. Trans-fat is the result of partial reduction of the double bond in unsaturated fats in food processing and are implicated in various chronic diseases such as CHD.

• Unsaturated fatty acids have one (mono-) or more (poly-) double valent bonds between adjacent carbons, have either a cis- or trans- arrangement at the double bond, come primarily from the plant kingdom, are liquid at room temperature, and are healthier than saturated fats.

Key points about lipids, con’t. • Cholesterol is a sterol that is a precursor to gonadal, corticosteroid

and mineralocortocoid hormones, bile, and fat soluble vitamins. High saturated fat in the diet increases de novo cholesterol formation and promotes atherosclerosis.

• Recommended dietary intake of lipids is ≤ 30% of total calories and ≤ 10% of total calories from saturated fat.

• Fat (intramuscular TAG and free fatty acids [FFA]) are the dominant energy substrate at rest and light/moderate intensity exercise. FFA is an important energy substrate during prolonged exercise.

• Carbohydrate depletion results in a decline in exercise intensity during prolonged aerobic exercise depending on the training adaptations that promote fat mobilization and oxidation.

• Aerobic training increases the ability to mobilize, transport, translocate and oxidize long-chain fatty acids.

• Enhanced fat oxidation allows the trained individual to use fat at greater exercise intensities, thus delaying glycogen depletion.

General structure of amino acidsCommon to

all amino acidsCommon to

all amino acidsCommon to all amino acids

Common to all amino acidsUnique to

each amino acid

Proteins• Amino acids are the “building blocks”• Peptide bonds link together amino acids

– Dipeptide is two amino acids joined together– Tripeptide is three amino acids joined together– Polypeptide is 50 to more than a 1000 amino acids

H2OThr-Val ValineThreonine

|H

OHThreonine Valine H2O

Thr-Val

OH|H

Formation of peptides and proteinSecondary Protein Structure

α-helix consists of a polypeptide backbone following a helical path with 3.6 amino acid residues per turn of the helix with the R moieties protruding outward.

β pleated sheets consists of protein strands interacting laterally via hydrogen bonds between the carbonyl oxygen and the amino hydrogen atoms. The N-termini of both strands may be at the same or opposite ends.

http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb1/part2/protein.htm

















Formation of peptides and proteinTertiary protein structure: three dimensional folding of a protein due to interactions (hydrogen, van der Waals, ionic, disulfide bonding) between amino acids located near or far apart in the primary structure

Quaternary protein structure: association of two or more identical or different polypeptide chains to form a complex stabilized by weak interactions between residues exposed on surfaces polypeptides within the complex.

The active site on enzymes may involve amino acid residues from different chains. The function of a protein (e.g., active site on an enzyme, troponin/tropomyison in muscle contraction) generally involves conformational shifts in polypeptides in the quaternary structure.


















Essential Amino Acids• Amino acids that the body cannot synthesize

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

Histidine Isoleucine Leucine

Lysine Methionine

Essential Amino Acids

Phenylalanine Threonine

Tryptophan Valine

Protein Sources• Complete proteins contain all of the essential amino acids

– Eggs, milk, fish, and poultry• Incomplete proteins lack one or more of the essential

amino acids– Vegetables such as lentils, dry beans and peas, nuts,

and cereals– Vegans must combine plant protein sources

(complimentary proteins)• An essential amino acid that is in limited supply in a

particular food is a limiting amino acid• Legumes (Methionine) • Grains (Lysine)• Corn tortillas (enchiladas) with refried beans

would be an example of complimentary proteins

Essential and nonessential amino acids

• Two main classes of amino acids– Essential

(indispensable) amino acids which must be obtained from foods in the diet

– Nonessential (dispensable) amino acids which may be formed in the body

**May be synthesized at an inadequate rate during times of stress so more is needed in the diet

**

Example Food Label

% Protein = 3 g · 4 kcal·g-1 ÷100 kcal = 10.9 %

Protein sources in the typical American diet

Daily Recommended Protein Intake• Normal protein requirements are

– 0.8 – 1.0 g protein·kg body mass-1

– Acceptable macronutrient distribution range = 10-35% of total caloric intake

– This range provides the opportunity for all individuals from the most sedentary to the most ardent bodybuilder/weight lifter to ingest adequate protein in a normal diet

– Stress, disease, and injury increase protein requirements• Many (but not all) experts and organizations recognize that

training to promote lean tissue growth may require 1.4-1.8 g protein·kg body mass-1

– Excessive protein intake can have harmful side effects like strained liver and kidney function

– Increases urea formation from amino acid deamination

Digestion and absorption of proteinStomach: HCl + pepsinogen → Pepsin. Enzymatic hydrolysis of protein to polypeptides and peptides

Small Intestine (Duodenum): Trypsin and chymotrypsin. Pancreatic proteases, continued enzymatic hydrolysis of peptides to individual amino acids

+ H2O

Absorption by the villi of the small intestinal epithelial cells through to the blood.

Digestion and absorption of protein

Role of Protein in the Body• Protein makes up 12-15% of body mass• Major sources of body protein

– Blood plasma (albumin, globulin)– Incorporation of nitrogen into NAD+, FAD, porphyrin

hemoglobin ring, catecholamine formation, and serotonin formation

– Connective tissue (collagen)– Enzymes (globular protein) – Receptors– Peptide hormones – Muscle (actin, myosin, troponin/tropomyosin) – Blood clotting (thrombin, fibrin, fibrinogen)

Protein Metabolism

• Process of deamination (nitrogen removal) forms urea which leaves body as urine

• Remaining carbon skeletons from deamination follow one of three diverse biochemical routes– Gluconeogenesis (glucogenic amino acids)– Energy source (glucogenic/ketogenic amino acids)– Fatty acid synthesis from acetyl CoA

• Excessive protein catabolism promotes fluid loss

Nitrogen Balance• NB = Dietary N Intake – Urinary N excretion – Fecal N

excretion – Sweat N excretion • Occurs when nitrogen intake equals nitrogen excretion

– Positive nitrogen balance (protein used for structure)• Growing children• During pregnancy• Recovery from illness• During resistance exercise training

– Negative nitrogen balance (protein catabolism for energy)• Diabetes• Fever• Burns• Dieting• Growth• Steroid use• Recovery from illness

Alanine

α-ketoglutarate

GlutamatePyruvate

Transaminase Reaction

Alanine Transaminase

Amino Acid Keto Acid

Keto Acid Amino Acid

http://www.xamplified.com/krebs-cycle/

Alanine (G),Threonine (G),

Glycine (G), Serine (G), Cysteine (G)Acetoacetyl

CoA

Phenylalanine (G/K),

Tyrosine (G/K), Lysine (K)

Aspartate (G), Asparagine (G)

Glutamate(G)

Arginine (G),Histidine (G), Glutamine (G),

Proline (G)

Isoleucine (G),Methionine (G),

Valine (G)

Leucine (K), Tryptophan (K)

Phenylalanine (G/K), Tyrosine

(G/K)

Oxidative catabolic fate of hydrocarbon skeletons of amino acids

DegradationExercise Group <

Control Group

SynthesisExercise Group >

Control Group

Effect of exercise and recovery on protein degradation and synthesis

Protein sparing effect of carbohydrates

Alanine-Glucose Cycle

Lactate Pyruvate

Alanine α-ketoglutarate

Glutamate

Alanine TransaminaseNAD+

NADH H+

Lactate Dehydrogemase

Cori Cycle and Gluconeogenesis

From Muscle to Liver-Cori Cycle

Alanine From Muscle to Liver; deamination to pyruvate-Gluconeogenesis from carbon skeletons of glucogenic amino acids

+ ATP

ADP+PO32-

Pyruvate

Oxaloacetate

Phospho-enolpyruvate

GTP+CO2

GDP

Pyruvate Carboxylase

Phosphoenol-pyruvate

Carboxykinase

Enolase H2O

2-Phosphoglycerate 3-Phosphoglycerate

PhosphoglycerateMutase

ATP

ADP PhosphoglycerateKinase

1,3-bisphospho-

glycerate

NADH H+

NAD+

PO32- Glyceraldehyde 3-P

Dehydrogenase

Glucose

TrioseIsomerase

Aldolase

Glyceraldehyde 3-P

DihydroxyacetonePhysphate

Fructose 1,6 bisphosphate

Fructose 1,6 bisphosphatase

Fructose-6- phosphate

Glucose-6- phosphate

Phosphoglucose Isomerase

Glucose 6 Phosphatase

H2O

PO32-

H2O

PO32-

Key points about protein • In addition to carbon, hydrogen, and oxygen, protein contains

nitrogen, sufer, iron, and phosphorous• The basic protein unit is the amino acid. Amino acids are the

alphabet for a diverse number of proteins with different structured and functions. Proteins are arranged in a primary, secondary, tertiary and quaternary structures.

• Humans lack the metabolic pathways to synthesize nine essential amino acids. The remainder can be synthesized by the human body.

• Complete (a.k.a. high quality) proteins contain all essential amino acids. Complete proteins are found in the animal kingdom.

• Sufficient protein can be obtained from plant sources by combining complimentary proteins.

• The liver synthesizes new glucose from amino acids deamination (carbon skeletons) in a pathway known as gluconeogenesis.

• The RDA for the normal adult is ~0.83 g kg·body mass-1.

Key points about protein, con’t. • Although experts disagree on the need for additional dietary

protein above the normal RDA by resistance and endurance athletes during intense training, many recommend ~1.2-1.8 g kg·body mass-1.

• Glycogen depletion accelerates protein catabolism during exercise. Adequate carbohydrate intake spares protein for structure and regulatory functions.

• Branch-chain amino acids can be metabolized in muscle and play a role in energy metabolism during exercise.

Protein Supplements in Weight Gain and Intense Training – Needed or Not?Caloric Intake for a 70 kg (154 lb) 18 yo male to gain 1 lb·week-1

Energy Expenditure kcal Energy needed to maintain 70 kg=679+(15.3·kg) Est REE 1750Resistance training=200 kcal·session-1 ·4 sessions·wk-1÷7 d 114Aerobic Training=300 kcal·session-1 ·4 sessions·wk-1÷7 d 171Muscle Tissue Growth = 3500 kcal·lb-1÷7 days 500Thermic Effect of Food=(7.5%·CHO)+(25%·Pro)+(2.5%·Fat) 247Total Energy Intake to meet Energy Expenditure 2783Carbohydrate Calories 60% (AMDR = 45-65%) 1670Fat Calories 25% (AMDR = 20-35%) 696Protein Calories 15% (AMDR = 10-35%) 417Carbohydrates (g) 417Fats (g) 77Protein (g) [includes ~1 g·kg-1 (normal needs) + ~14 g (new muscle growth) + ~20 g (post-exercise repair)]

104

Protein (g·kg-1) 1.5

chapter01-carbohydrates lipids proteins

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