Nutrition and Energy Metabolism in Exercise

1
Nutrition and Energy Metabolismin Exercise
2
Energy for Sport Preferred Fuels and Overall
Energy Requirements
Photo courtesy of http//www.bodylab.co.nz/VO2max/
VO2max.htm
3
How Do We Go From Eating Food to Powering Muscles?

• Digestion of food
• Absorption of nutrients from intestine into blood
• Uptake of nutrients from blood into muscle cells
• Use of nutrients to generate adenosine
  triphosphate (ATP)the energy currency of cells

a High energy bonds in red.Adapted from
http//commons.wikimedia.org/wiki/FileATP_structu
re_revised.png
4
Pathways for Your Body to Generate ATP From
Nutrients

• Which process is dominant during exercise?
• Depends on oxygen availability
• Affected by training and nutrient stores available

5
Creatine Phosphate Pathway

• Creatine stores may be a limiting factor for
  adenosine triphosphate (ATP) synthesis during
  explosive, high-intensity activities
• Creatine plays a role in maximal effort lasting
  up to 10 sec
• Key dietary issues include maintaining and
  maximizing creatine stores in muscle

6
The Creatine Phosphate Pathway and Breakdown of
Creatine Phosphate to Creatinine

• 3 different types (isoforms) of creatine kinase
  (CK)
• CK-BB, or CK-1 (brain, lung)
• CK-MB, or CK-2 (cardiac)
• CK-MM, or CK-3 (skeletal muscle)

Net result from creatine phosphate breakdown 1
ATP
Abbreviations ADP, adenosine diphosphate ATP,
adenosine triphosphate CPK, creatine
phosphokinase. Reprinted from Smith C, et al.
Marks Basic Medical Biochemistry A Clinical
Approach. 2nd ed. Philadelphia, PA Lippincott
Williams Wilkins 2005870-871.
7
Aerobic and Anaerobic Glycolysis
Anaerobic
Aerobic
Glycogen
Dietary Glucose
Glucose (6-carbon)

• 2 ATP required (1 if starting from glycogen
• 4 ATP generated from SLP
• 2 NADH H enter electron transport chain to
  produce ATP

• 2 ATP required (1 if starting from glycogen)
• 4 ATP generated from SLP
• 2 NADH H used to form lactate from pyruvate

Net result and2-3 ATP
Pyruvate (3-carbon)
Pyruvate (3-carbon)
Net result 5-7.5 ATP from SLP and NADH H
Abbreviations ATP, adenosine triphosphate, H,
hydrogen NADH, reduced form of nicotinamide
adenine dinucleotide SLP, substrate-level
phosphorylation. Data from Salway JG. Metabolism
at a Glance. 3rd ed. Maldern, MA Blackwell
Publishing 200420-21.
8
Hydrogen and electron carriers an important link
between B-vitamins and energy production

• Nicotinamide adenine dinucleotide (NAD)
• The B-vitamin niacin is part of its structure
• Can donate hydrogen and electrons for synthesis
  of adenosine triphosphate (ATP)
• Reduced form is symbolized as NADH H
• Worth 2.5 ATP when entering electron transport
  system
• Flavin adenine dinucleotide (FAD)
• The B-vitamin riboflavin is part of its structure
• Can donate hydrogen and electrons for synthesis
  of ATP
• Reduced form is FADH2
• Worth 1.5 ATP when entering electron transport
  system

9
ATP Yields Glucose to Pyruvate
Starting from
OR
Abbreviations ATP, adenosine triphosphate H,
hydrogen G-P, glucose to pyruvate NADH, reduced
form of nicotinamide adenine dinucleotide SLP,
substrate-level phosphorylation.Data from Salway
JG. Metabolism at a Glance. 3rd ed. Maldern, MA
Blackwell Publishing 200420-21.
10
Fate of Pyruvate

• Aerobic
• Enters mitochondria
• Converted to acetyl coenzyme A (CoA)
• This reaction generates 1 NADH H
• Thiamin is a coenzyme for pyruvate dehydrogenase
  (PDH)
• Acetyl fragment enters tricarboxylic acid (TCA)
  cycle
• Anaerobic
• Converted to lactate using hydrogen and electrons
  donated from NADH H

Abbreviations H, hydrogen NADH, reduced form
of nicotinamide adenine dinucleotide.
11
ATP Yields Pyruvate to Acetyl CoA

• This conversion is mediated by PDH, a
  thiamin-dependent enzyme
• Each of the 2 pyruvate molecules from glucose
  metabolism can be converted to acetyl CoA

Pyruvate
NAD
NADH H
CO2
Acetyl CoA
Abbreviations ATP, adenosine triphosphate CO2,
carbon dioxide CoA, coenzyme A H, hydrogen
NAD, nicotinamide adenine dinucleotide PDH,
NADH, reduced form of NAD PHD, pyruvate
dehydrogenase.Data from Salway JG. Metabolism at
a Glance. 3rd ed. Maldern, MA Blackwell
Publishing 200421.
12
Fate of NADH H

• Aerobic
• Can enter the mitochondrion
• Donates hydrogen and electrons to the electron
  transport system (ETS) for synthesis of adenosine
  triphosphate (ATP)
• Anaerobic
• Donates hydrogen and electrons to pyruvate to
  form lactate (enzyme is lactate dehydrogenase
  LDH)

Abbreviations H, hydrogen NADH, reduced form
of nicotinamide adenine dinucleotide.
13
Lactate Accumulation and Lactate Threshold
(Trained vs Untrained Subjects)
Abbreviation VO2 max, peak exercise oxygen
consumption. Reprinted from McArdle WD et al.
Exercise Physiology Nutrition, Energy, and Human
Performance, 7th ed. Philadelphia, PA Lippincott
Williams Wilkins 2010163.
14
Fate of Lactate Not the bad guy it was always
made out to be!

• Lactate accumulates in blood as rate of muscle
  production exceeds rate of clearance/utilization
• Lactate formation is NOT the cause of the
  lowering of muscle pH that occurs during exercise
• Lactate accumulation occurs simultaneously with
  other factors that do lower muscle pH (i.e.,
  cause accumulation of H)
• One example is the release of H that occurs when
  ATP is hydrolyzed for energy
• During recovery or slowing of exercise, a portion
  of lactate can be converted first to pyruvate
  and then back to glucose(the Cori cycle)
• Occurs mainly in the liver

15
The Tricarboxylic Acid (TCA) Cyclea
Net result 1 turn of the cycle 3 NADH, 1 GTP,
1 FADH2, and 2 molecules of CO2 released
a Also known as the Krebs or citric acid
cycle. Abbreviations ATP, adenosine
triphosphate C, carbon CO2, carbon dioxide
CoA, coenzyme A FAD, flavin adenine
dinucleotide FADH, reduced form of FAD GDP,
guanosine diphosphate GTP, guanosine
triphosphate. NAD, nicotinamide adenine
dinucleotide NADH, reduced form of
NAD. Reprinted from Alberts B, et al. Essential
Cell Biology, 2nd ed. London Garland Science
2004chapt 13.
16
The Electron Transport System (ETS)
Intermembrane space
Inner membrane
Mitochondrial matrix
Abbreviations ADP, adenosine diphosphate ATP,
adenosine triphosphate e, electron FAD, flavin
adenine dinucleotide H, hydrogen NAD,
nicotinamide adenine dinucleotide O, oxygen P,
phosphate. Reprinted from http//student.ccbcmd.ed
u/gkaiser/biotutorials/energy/fg5.html.
17
ATP Yields TCA Cycle

• TCA cycle (mitochondria) subtotal

Acetyl CoA
citrate
oxaloacetate
3 NADH H 1 FADH2 1 GTP 2 CO2
Abbreviations ATP, adenosine triphosphate CO2,
carbon dioxide CoA, coenzyme A FADH2, reduced
form of flavin adenine dinucleotide GTP,
guanosine triphosphate H, hydrogen NADH,
reduced form of nicotinamide adenine
dinucleotide SLP, substrate-level
phosphorylation TCA, tricarboxylic acid.Data
from Salway JG. Metabolism at a Glance. 3rd ed.
Maldern, MA Blackwell Publishing 200421.
18
Energy Metabolism of Fatty Acids

• Digestion and absorption of triglycerides
• Hydrolysis of triglyceride by lipases
• Medium-chain fatty acids Absorbed directly into
  blood
• Long-chain fatty acids Absorbed first into
  lymphatic system, then blood
• Fatty acids enter cells, join with CoA
  (activation), and enter mitochondria
• Long-chain fatty acids Require a carnitine
  transporter to get into mitochondria
• Process of cutting the fatty acid down into
  successive 2-carbon units (each becomes acetyl
  CoA)
• Called ß-oxidation
• Acetyl CoA units are then metabolized the same
  way via TCA cycle and ETS as previously described
  for glucose

Abbreviations CoA, coenzyme A ETS, electron
transport system TCA, tricarboxylic acid.
19
Medium chain triglycerides/fatty acids

• Medium chain fatty acids (10-12 carbons or less)
  have unique properties compared with long chain
  fatty acid regarding their absorption and
  metabolism
• Absorbed directly into the portal blood versus
  lymphatics (more water soluble)
• Transported directly to liver following
  absorption
• Do not require a transporter (e.g., carnitine
  transporter) to enter the mitochondria for
  oxidation
• Metabolized more like a carbohydrate than a fat
• Potential alternate energy source for working
  muscles, but a key problem is getting these fatty
  acids to peripheral tissues
• Potential solution Structured triglyceride
• Alters position of medium chain fatty acids on
  glycerol backbone
• Greater inclusion in lymphatics for transport to
  periphery

20
Putting It All Together Glucose and Fatty Acid
Energy Metabolism
Abbreviations ATP, adenosine triphosphate CoA,
coenzyme A ETS, electron transport system
FADH2, reduced form of flavin adenine
dinucleotide H, hydrogen LDH, lactate
dehydrogenase NADH, reduced from of nicotinamide
adenine dinucleotide PDH, pyruvate
dehydrogenase TCA, tricarboxylic acid.
21
Putting It All Together ATP Yields per Mole
Glucosea
a ATP yields assuming optimal function of ETS. In
reality, however, electron leakage
occurs.Abbreviations ATP, adenosine
triphosphate CoA, coenzyme A ETS, electron
transport system FADH2, reduced form of flavin
adenine dinucleotide G-P, glucose to pyruvate
GTP, guanosine triphosphate H, hydrogen NADH,
reduced form of nicotinamide adenine
dinucleotide SLP, substrate-level
phosphorylation TCA, tricarboxylic acid.Data
from Salway JG. Metabolism at a Glance. 3rd ed.
Maldern, MA Blackwell Publishing 200421.
22
Putting It All Together ATP Yields With Palmitate

• Palmitate is a 16-carbon, saturated fatty acid
  (160)

Abbreviations ATP, adenosine triphosphate CoA,
coenzyme A FADH2, reduced form of flavin adenine
dinucleotide GTP, guanosine triphosphate H,
hydrogen NADH, reduced form of nicotinamide
adenine dinucleotide TCA, tricarboxylic
acid.Data from Salway JG. Metabolism at a
Glance. 3rd ed. Maldern, MA Blackwell
Publishing 200439.
23
Key Summary Points

• Metabolism of carbohydrate
• Pro Can support high-intensity exercise because
  glycolysis can occur without oxygen
• Cons Lactate build-up occurs carbohydrate
  stores are very limited in the body relative to
  fat
• Metabolism of fat
• Pros ATP yields are very large for fatty acids
  (generally gt 100 ATP/mol) versus glucose ( 32
  ATP/mol) very dense energy reserve (3,500 kcal
  1 lb body fat)
• Con Requires oxygen and the process of
  metabolizing fats is not as quick as glycolysis
  training required to enhance the bodys ability
  to access fat for energy during exercise

Abbreviation ATP, adenosine triphosphate.
24
Do We Use Protein for Energy?

• We can, but it is generally not desirable to do
  so
• Maybe 5 to 10 of total cost of exercise
  activity
• Mainly branched-chain amino acids (leucine,
  isoleucine, valine)
• Carbohydrate depletion increases amino acid
  oxidation
• Must remove the nitrogen (amino group) and
  excrete it (mainly as urea) before metabolizing
  the carbon skeleton
• Amino acids are typically either glucogenic
  (carbon skeletons convert to glucose) or
  ketogenic (carbon skeletons convert to acetyl CoA
  like fats do)

Abbreviation CoA, coenzyme A.
25
How Does the Body Decide What to Burn for Fuel at
a Given Time?

• Influenced by a number of factors
• Intensity of exercise and oxygen availability
• Fuel stores available (carbohydrate depletion)
• Hormonal influences (insulin, epinephrine,
  cortisol)
• Training effects regarding ability to deliver and
  use oxygen
• Muscle fiber make-up

26
Effect of Exercise Intensity on Substrate
Oxidation in Trained Men
300
Muscle glycogen
Muscle triglycerides
Plasma FFA
Plasma glucose
200
cal/kg/min
100
0
25
65
85
VO2 max,
Abbreviations FFA, free fatty acid VO2 max,
peak exercise oxygen consumption. Reprinted from
Romijn JA. Am J Physiol. 1993265(3 Pt
1)E380-E391.
27
Classification of Human Skeletal Muscle Fiber
Types
Adapted from McArdle WD et al. Exercise
Physiology Nutrition, Energy, and Human
Performance, 7th ed. Philadelphia, PA Lippincott
Williams Wilkins 2010371.
28
Energy Requirements of Athletes

• It is very difficult to estimate the energy
  requirements of different athletes
• Measuring kcals burned during physical activity
  is the most difficult
• Motion detectors, heart rate, portable
  spirometry, doubly-labeled water
• Growth requirements in younger athletes
  complicate the issue
• Trying to match reported energy intake with
  weight maintenance is also problematic
• Energy intake is frequently underreported in
  studies
• Reported energy intakes of athletes are highly
  variable
• Within athletes in a given sport
• Stage of training is an important factor
• Between athletes in different sports

29
Reported Energy Intake of Athletes
1. De Wijn FJ, et al. Bibl Nutr Dieta.
1979(27)143-148. 2. Papadokonstantaki M, et al.
World Rev Nutr Diet. 199371183-184. 3. Simonsen
JC, et al. J Appl Physiol. 1991701500-1505. 4.
Strauzenberg SE, et al. Bibl Nutr Dieta.
1979(27)133-142. 5. Short SH, Short RW. J Am
Diet Assoc. 198382(6)632-645. 6. Ntimof F.
Sports Nutrition. Jusantor, Sofie, 1987. 7.
Benardot D, et al. J Am Diet Assoc.
198989(3)401-403. 8. Grandjean AC. Am J Clin
Nutr. 198949(5 suppl)1070-1076 9. Chen JD, et
al. Am J Clin Nutr. 198949(5 suppl)1084-1089. Da
ta from Pavlou KN. Energy needs of the elite
athlete. World Rev Nutr Diet. 1993719-20.
30
Reported Energy Intake of Athletes (contd)
1. Mc Ardle WD, et al. Sports and Exercise
Nutrition, 3rd ed. Philadelphia, PA Lippincott
Williams Wilkins 2009chapt 7223. 2. Ziegler
P, et al. J Am Diet Assoc. 2001101(3)319-325. 3.
Ousley-Pahnke L, et al. J Am Diet Assoc.
2001101(3)351-354. 4. Rontoyannis GP, et al. Am
J Clin Nutr. 198949(5 suppl)976-979. 5.
Wolinsky I. Nutrition in Exercise and Sport, 3rd
ed. Boca Raton, FL CRC Press 1997. Adapted
from Mc Ardle WD, et al. Sports and Exercise
Nutrition, 3rd ed. Philadelphia, PA Lippincott
Williams Wilkins 2009chapt 7223.
31
Components of Energy Expenditure

• Basal Metabolic Rate (BMR)
• Energy needed to maintain vital body functions
• Typically measured after 8 hours of rest, 12 to
  18 hoursof fasting
• Almost the same as Resting Energy Expenditure
  (REE)
• REE measured 3 to 4 hours post-absorptive
• Within 10 of the BMR
• Equals roughly 3.5 mL O2 consumed/kg/min
• This is called 1 metabolic equivalent (MET)
• Exercise intensity often is measured as a
  multiple of resting (eg, 10 METS)
• Affected by surface area, the amount of fat-free
  mass, and metabolic efficiency (brown fat)

Abbreviation O2, oxygen.
32
Components of Energy Expenditure (contd)

• Thermic Effect of Exercise (TEE)
• Energy expended during voluntary physical
  activity
• Most variable component
• Can range from 0 to 50 or more of total energy
  requirement (TER)
• For a 70-kg person cycling at 15 mph, energy
  expenditure is 7 BMR, or 7 METS
• Diet-Induced Thermogenesis (DIT)
• kcals needed to digest, absorb, and store
  nutrients
• About 5 to 10 of BMR
• Non-exercise Activity Thermogenesis (NEAT)
• kcals burned during behaviors like fidgeting
• Can sometimes account for 400 to 500 kcal/d

Abbreviations BMR, basal metabolic rate METS,
metabolic equivalents.
33
Estimating Energy Expenditure

• Can measure TER via doubly labeled water
• Expensive
• Can measure BMR via indirect calorimetry and
  multiply by factors
• Must have indirect calorimeter
• 1 L O2 consumed ? 5 kcals
• Can determine EER using equations
• US Institute of Medicine (IOM) has developed
  equations for Estimated Energy Requirement (EER)
  based on age, sex, height, weight, and physical
  activity level1
• They have 7 separate DRI volumes for energy and
  various nutrients
• All can be read online (tedious) or purchased as
  individual hard copies
• The summary hard copy (condensed version) of all
  the DRI reports can be helpful

Abbreviations BMR, basal metabolic rate DRI,
dietary reference intake TER, total energy
requirement. 1. Institute of Medicine of the
National Academies. Dietary Reference Intakes
The Essential Guide to Nutrient Requirements.
National Academies Press Washington DC.
34
IOM Physical Activity Levels (PAL) and
Coefficients (PA)
Plug one of these values into the EER equation
a PAL is a multiple of basal energy expenditure
and is used to determine the applicable PA on
this table. Abbreviations ADL, activities of
daily living, EER, estimated energy requirement
IOM, Institute of Medicine PA, physical activity
coefficient PAL, physical activity
level. Reprinted from Institute of Medicine of
the National Academies. Dietary Reference
Intakes The Essential Guide to Nutrient
Requirements. National Academies Press
Washington DC 200684.
35
IOM Equations for EER
Abbreviations EER, estimated energy requirement
IOM, Institute of Medicine PA, physical activity
coefficient. Reprinted from Institute of Medicine
of the National Academies. Dietary Reference
Intakes The Essential Guide to Nutrient
Requirements. National Academies Press
Washington DC 200682.
36
Example of Energy Requirement Calculation

• Very active 20-year-old female 132 lb (60 kg)
  5, 5 tall (1.4 m)
• PA 1.45a
• EER 354 (6.91 age yr) PA (9.36
  weight kg) (726 height m)b
• EER 354 (6.91 20) 1.45 (9.361 60)
  (726 1.4)
• EER 354 138.2 1.45 561.66 1,016.4
• EER 215.8 2,289.18
• EER 2,504 kcal

a From IOM PA table.1 b From IOM EER
table.1 Abbreviations EER, estimated energy
requirement IOM, Institute of Medicine PA,
physical activity coefficient. 1. Institute of
Medicine of the National Academies. Dietary
Reference Intakes The Essential Guide to
Nutrient Requirements. National Academies Press
Washington DC 2006537.
37
Example of Simplified Energy Requirement
Calculation

• Previous calculation to estimate EER is lengthy,
  cumbersome
• Simplified calculation to estimate TER
• TER weight (kg) 40 to 60 kcal/kg/day
• Very active 20-year-old female 132 lb (60 kg)
  5, 5 tall (1.4 m)
• Using 40 kcal/kg
• TER 60 40 kcal/kg 2,400 kcal/day
• Using 45 kcal/kg
• TER 60 45 kcal/kg 2,700 kcal/day
• Using 50 kcal/kg
• TER 60 50 kcal/kg 3,000 kcal/day
• Using 60 kcal/kg
• TER 60 60 kcal/kg 3,600 kcal/day

Abbreviations EER, estimated energy requirement
TER, total energy requirement.
38
Energy Expenditure in Athletes Considerations

• Without direct measurement of energy expenditure,
  equations offer only a rough estimate
• Monitor weight of the athlete on a particular
  energy intake and adjust the energy intake
  accordingly depending on whether weight gain,
  maintenance, or loss is desired
• Most people, including athletes, underreport food
  intake and over report physical activity when
  questioned
• 1 lb body fat ? 3,500 kcal
• For weight loss, target gradual weight loss when
  possible (1 lb/week is a good goal)
• Avoids loss of lean tissue that can happen with
  more rapid weight loss
• Loss of 1 lb/week 500 kcal/day deficit
• For example, reduce food intake by 250 kcal/day
  and increase physical activity by 250 kcal/day

39
Supplementary Slide on ATP and muscle contraction
40
ATP Role in Muscle Contraction
Abbreviations Ach, acetylcholine ADP, adenosine
diphosphate ATP, adenosine triphosphate Ca2,
calcium. Reprinted from McArdle WD, et al.
Exercise Physiology Nutrition, Energy, and Human
Performance, 7th ed. Philadelphia, PA Lippincott
Williams Wilkins 2010370.