Energy Balance/Metabolism (Day 1)

Question 1

What is energy?

Answer 1

capacity to do work (chemical, transport, mechanical)

• maintain ion gradients (ex. Na/K pump)
• Maintenance and repair (ex. protein synthesis)
• Movement (muscle contraction)
• Reproduction
• Lactation
• Thermogenesis

Question 2

What is metabolism?

Answer 2

overall energy economy in a cell or organism (ex. the sum total of all energy-obtaining and energy-consuming process –> metabolic rate)

• catabolism
• anabolism

Question 3

Catabolism

Answer 3

part of metabolism
–>breakdown of macromolecules (fuels) to obtain usable energy –> ATP

big molecules –> small molecules + ATP

in aerobic organisms, the final common pathway whereby the chemical energy in fuel molecules is conserved as ATP is called RESPIRATION

Question 4

Anabolism

Answer 4

part of metabolism
–> use of energy (ATP) to produce new macromolecules

small molecules + ATP –> big molecules

Question 5

Respiration

Answer 5

a process of slow, controlled combustion (oxidation)

Question 6

Krebs/Citric Acid Cycle

Answer 6

Rotary engine of metabolism

ALL macronutreints feed into a final, common pathway (glucose is basic metabolic fuel)

Question 7

Energy content of food: Direct Calorimetry

Answer 7

1 Calorie = 1000 calories = 1 kcal = 2.184 kJ

amount of heat needed to raise temp of 1 liter of water by 1 degree C

yields “gross” energy of food

includes combustion of indigestible components (ex. fiber)

Question 8

Gross Energy Content

Answer 8

adjusted for indigestible components and for any other relevant losses, then this modified value is used on food labels

Question 9

Energy content of metabolic fuels

Answer 9

CHO: 4 kcal
PRO: 4 kcal
FAT: 9 kcal

–>PRO not usually used for energy, but preferably for protein synthesis

Question 10

Energy Expenditure: indirect calorimetry

Answer 10

since combustion (oxidation) of fuels to provide energy and use the use of that energy requires O2
--> then rate of O2 consumption can be used to measure metabolic rate

• 1 liter O2 consumed per 4.5-5 kcal released from metabolized food
• Metabolic rate (kcal/day) = L O2 consumed/day x 2.8kcal/L O2

Question 11

BMR

Answer 11

minimal rate for maintaining life, aka SMR (12 hrs postabsorptive state, resting)

Question 12

What influences metabolic rate?

Answer 12

Age: decreases with age

Sex

Lean muscle mass: as LMM increases so does MR

Diet: eating meal increases MR via thermal effect of food

Hormones: thyroid hormones, epinephrine, norepinephrine

Genetic Factors: poorly characterized

Question 13

Metabolism recep

Answer 13

overall biochemical processes mediating disposition of macronutrients

oxidation for energy vs. biosynthesis vs. storage

Question 14

Fed (absorptive) state

Answer 14

anabolic

fuels from food – oxidation –> ATP/storage

increase of blood glucose

Question 15

Fasted (postabsorptive) state

Answer 15

catabolic

body stores – oxidation –> ATP

decrease of blood glucose

Question 16

How is energy stored in the body? CHO

Answer 16

glycogen in liver and muscle vis glycogenesis – reverse process is glycogenolysis

Question 17

How is energy stored in the body? FAT

Answer 17

triglycerides in adipose

Question 18

What determines fed vs fasted state?

Answer 18

blood glucose levels –> ratio of insulin: glucagon (counter-regulatory hormones)

Question 19

Why is glucose so important?

Answer 19

• major metabolic fuel for all tissues, obligatory fuel for RBCs, renal medulla, and under non-starvation conditions, the brain
• sole food for muscle contraction under “fight or flight” conditions
• provides anaplerotic precursors for citric acid (TCA) cycle –> an anaplerotic reaction is one which feeds intermediates into TCA cycle
• provides carbon skeletons for synthesis of nonessential AA
• provides carbon precursors for TG componenets (glycerol and FA)

Question 20

Fate/uses for glucose

Answer 20

precursor for DNA, RNA

ATP production

Glycogen (storage)

FA (stroage)

AA

Question 21

Fate of fuels: FED state, CHO

Answer 21

HIGH insulin, LOW glucagon

CHO:

1. increases glucose uptake by cells form blood
2. increased glucose utilization for ATP production
3. increases glycogenesis in liver, muscle (storage as glycogen)
4. increased lipgenesis in liver (conversion of glucose to FA)

Question 22

Fate of fuels: FED state, FAT

Answer 22

HIGH insulin, LOW glucagon

FAT: FA + glycerol — TG storage in adipose

Question 23

Fate of fuels: FED state, PRO

Answer 23

HIGH insulin, LOW glucagon

PRO: AA used strictly for PRO synthesis, any excess not used for PS are deaminated and carbon skeletons used for energy production for fat synthesis

Question 24

Fate of fuels: FASTED state, CHO

Answer 24

LOW insulin, HIGH glucagon

CHO:

1. decreased glucose uptake by cells from blood
2. decreased glucose utilization for ATP production
3. decreased glycogenesis in liver, muscle (ex. decreased glycogen storage)
4. decreased lipogenesis, increased lipolysis (liver)
5. increased glycogenolysis in liver, muscle (increased breakdown of glycogen stores)
6. increased gluconeogenesis

Question 25

Fate of fuels: FASTED state: FAT

Answer 25

LOW insulin, HIGH glucagon FAT: TG --> FA + glycerol in adipose, FA + glycerol --> liver

Question 26

Fate of fuels: FASTED state, PRO

Answer 26

LOW insulin, HIGH glucagon PRO: increased protein breakdown, AA carbon skeletons used for glucogeogenesis

Question 27

FED vs. FASTED

Answer 27

Fed: INSULIN: glucagon --> glucose utilization and storage as glycogen/fat Fasted: Insulin: GLUCAGON --> breakdown of stored fat, glycogen and production of new glucose

Question 28

So, during fasting, where does the carbon needed for gluconeogenesis come from, if it can’t come from fat??

Answer 28

body protein PRO --> AA --> c-skeletons --> glucose

Question 29

Nitrogen excretion: Urea cycle

Answer 29

PRO: nitrogen disposal problem, NH3, NH4 are toxic/require large amount of water for direct excretion (ex. fish) Urea formation in liver - energetically costly, but avoids ammonia toxicity --> AAs stripped of NH3, NH3 converted to less toxic formula and excreted

Question 30

What is needed to keep TCA cycle going?

Answer 30

GLUCOSE If glucose is insufficient, the cycle slows --> less ATP produced (this has implications for fat use during fasting/starvation)

Question 31

Ketosis

Answer 31

incomplete oxidation of FA, due to combo of low levels of incoming glucose + high levels of incoming FA --> brain uses detests for energy under starvation conditions

Question 32

Ketone Bodies

Answer 32

alternative source of energy for brain, but prolonged high systemic levels can be detrimental at high plasma levels, kidney is unable to completely reabsorb KB --> net energy loss to body KB are organic acids --> metabolic acidosis Kidney can acidify urine to only pH 4.5-5, thus only about 1/2 of excreted KB are in acid form --> reminder but have a cation (ex. Na, K) --> ionic depletion

Question 33

Energy Stores

Answer 33

Ready reserves: work for seconds only ex. creatine kinase, phosphocreatine, ATP Long-term: work for minutes/months ex. CHO, FAT, PRO

Question 34

Priorities during fasting/starvation

Answer 34

1. Maintain blood glucose | 2. conserve body protein

Question 35

Energy stored as fat

Answer 35

5: 1 compared to PRO 160: 1 compared to CHO