Introduction to Energy Balance Flashcards Preview

DEMS > Introduction to Energy Balance > Flashcards

Flashcards in Introduction to Energy Balance Deck (17):
1

How do you measure RMR?

• Indirect calorimetry
• Measure respiratory gas composition and flow rates to estimate O2 consumption and CO2 production
• The amount of oxygen consumed by a person at rest is an indirect measure of energy expenditure
• RMR can be ESTIMATED from formulae using age, sex, height and weight
• More accurate with lean body mass

2

How do you measure a given nutrient's TEF?

• Thermal effect of food, essentially how much energy it takes to digest that nutrient
• Protein highest, fat lowest
• You measure by indirect calorimetry the increment of energy expenditure above RMR following ingestion of a defined test meal

3

What are the components of energy balance?


• TEE = total energy expenditure
○ Made up of three components
• RMR = Resting metabolic rate
○ 75% of total energy expenditure in sedentary people
○ Energy cost of keeping Na and K where they belong, keeping the heart pumping, keeping body temp constant and other basic functions
○ Primary determininant = fat free mass (lean body mass)
○ b/c liver, heart, kidney, brain and skelatal muscle are the most metabolically active
○ Always variability among people
• TEF = thermal effect of food
○ Roughly 8% of total expenditure
○ Cost of digesting and distributing nutrients from the diet to tissues of the body
○ Protein has the higest energy cost of digestion, then carbs then fat
• EEPA = energy expended in physical activity
○ Most variable component
○ Highly active people, may be 30-40% of total daily expenditure
○ NEAT - non-exercise activity thermogenesis is one component of this
§ From fidgeting or movements performed doing other tasks
○ Ratio of work to total energy expended during physical activity is known as exercise/work efficiency

4

How do you measure total energy expenditure during work/exercise?

• Doubly labeled water
• Measures oxygen consumption in free living individuals over a period of weeks
• Subtract RMR and TEF from TEE, you can estimate EEPA
• Physical activity levels can also be estimated by physcial activity questionnaires
• Amount of activity done, though not energy value, can be measured by pedometers accelorometers or GPS monitors

5

Are the current methods for measuring energy intake good or bad?

• Current methods are poor
• Most studies rely on self-reported food intake which is unreliable
• Most people under-report by 20-40%

6

What is super important about EI = TEE?

*because there are not great ways of measuring intake...
• Energy intake = Total energy expenditure
• IF the person's weight is stable
• Thus, measuring TEE with double labeled water is an accurate prediction of energy intake if that person's weight is stable

7

You need to know how the body handles what three nutrients like the back of your hand?

• Glucose
• Fatty acids
• Amino acids

8

What are the body's energy stores?

• Fat, glycogen or protein
• Fat stores contain the greatest amount of stored energy, roughly 120,000 kcal in a normal weight individual
• Glycogen in muscle and liver is main storage area

9

Why, when a person is in persistant negative energy balance, do they break down muscle?

• No great body store for protein
• If starved for protein the body will break down muscle for protein
• The amino acids will be converted to glucose in the liver
• Brain is the most hungry organ and it desires glucose
• 30% reduction of body protein is severe malnutrition bordering on death

10

What is the most accurate way of measuring body composition?

• DEXA
• Dual energy x-ray absorptiometry

11

What is the hierarchy of nutrient oxidation?

• This has to do with what the body prefers as an energy storage mechanism
• Protein, when taken in excess, is oxidized in preference to carbohydrate or fat
• If protein balance is there, fat and carbs overfed, then carbohydrates will be preferentially oxidized to store fat
• Smaller capacity for storing excess carbs as glycogen and carbs can be converted to fat for more long-term storage
○ End result is positive energy balance leads to fat accumulation
• Conversely, negative energy balance will be prioritized to make glucose for the brain
○ End result is lacking essential amino acids, essential fatty acids and micronutrients that become depleted during poor energy intake
○ Organ dysfunction and disease

12

What are the main forms of energy currency in cells?

• ATP
• And NADH, NADPH, FADH2 to a lesser extent

13

When considering catoblism of the main nutrients, what questions should you be asking yourself?

• What is the tissue of origin?
• What is the stimulus for release?
• What is the relevant tissue destination?
• What are the sizes of the relevant pools of this nutrient?

14

Describe the general overview of carbohydrate use and digestion

• Glucose is an important source of energy for many tissues
• Primary source of energy for brain, so stable concentration is super important
• Glycolysis
○ Glucose is present in excess in the blood relative to intracellular concentration
○ Enters the cell and moves down pathway of glycolysis
○ IN THE CYTOPLASM
○ Breakdown of 6 carbon parent molecule to two three-carbon molecultes of pyruvate with the reulting production of a modest amount of energy in the form of ATP and the energy carrying molecule NmADH
○ If oxygen is not present or if no mitochondria, pyruvate is converted to lactate which leaves the cell to regenerate NADH
Anaerobic metabolism
• TCA cycle
○ Presence of oxygen and mitochondria, three carbon end-product of glycolysis (pyruvate) enters TCA
○ Tricarboxylic acid cycle
○ More energy in pyruvate extracted here
○ Through a group of reactions that result in the production of CO2, GTP (converted to ATP), NADH and FADH2

• Electron Transport
○ Series of proteins in the inner membrane of the mitochondria that take the NADH and FADH2 produced in the TCA cycle to produce ATP from ADP
○ Consume oxygen to produce water in a process known as oxidative phosphorylation

• Gluconeogenesis
○ Body is state of negative energy balance and needs to have new glucose production
○ Uses a range of carbon skeletons from other tissues including lactate
§ Glycolysis
○ Also carbon skeletons from amino acids that come from muscle to essentially perform the reactions of glycolysis in reverse
○ Thus, lactate and amino acids from peripheral tissues can be converted by liver and kidneys into glucose for use by the brain during periods of fasting

• Glycogen
○ Glucose available in excess it can be stored in the form of glycogen which is a polymer of glucose
○ Most is in the liver and skelatal muscle
○ Used for immediate sources of energy for brain and muscle exercise

• Pentose Phosphate Pathway (hexose monophosphate shunt)
○ Detour from the path of glycolysis
○ Activate dwhen glucose is present in excess or there is a need for the molecules that the pathway provides
○ Generates NADPH and ribose
○ NADPH provides energy for synthesis of fatty acids and steroid hormones
○ Important for defending cells against oxidative stress and in pathogen killing by WBCs
Ribose-5-phosphate produced by this pathway is a key step in nucleotide synthesis, so it's a building block of RNA and DNA

15

Describe Triacylglyceral breakdown in general

• Triacylglycerol degradation
○ Beta-oxidation and ketogenesis
○ When the body is in negative energy balance
○ Stored fat in the form of triglyceride in adipose tissue can provide energy to oxidizing tissues such as skelatal muscle and liver as al alternative to glucose
○ Allows circulating glucose to preferentially be available to brain which can't oxidize fat directly
○ In the liver the energy provided by fat oxidation can be used to provide the energy necessary for gluconeogenesis which is an eergy consuming set of reactions
○ In adipose tissue, triglyceride is broken down to fatty acids and glycerol that are released into the circulation
○ Fatty acids are then taken up by tissues like liver and muscle where they are catabolized two carbons at a time in beta-oxidation
§ End-product here is acetyl coA which enters TCA cycle to generate NADH and FADH2
§ These then entery electron transport for ATP production
○ Alternative product of fatty acid breakdown is ketone bodies
§ When insulin is low and counter-regulatory hormones are very high
§ Alternative brain fuel during prolonged fasting and in uncontrolled type 1 diabetes

16

Describe the general pathways by which the body uses or stores fat

• Triacylglycerol synthesis
○ De novo lipogenesis
○ Fatty acids are the central building block of many lipid classes
○ When glucos is present in excess within a liver cell or adipocyte there can be a rise in acetyl-CoA
§ 2-carbon intermediate that enterys TCA cylce within mitochondria
○ Acetyl-CoA can be used to make fatty acids derived from glucos for storage in a process known as de novo lipogenesis
○ Fatty acids are then put together 3 at a time and the 3 carbon alcohol glycerol to make triglyceride
§ The form of fat that is tored in adipose tissue or is secreted from the liver in triglyceride rich lipoproteins
□ VLDL
○ This energy consuming process converts glucose, which the body has limited ability to stor, to fat which can be stored longer

• Triacylglycerol degradation
○ Beta-oxidation and ketogenesis
○ When the body is in negative energy balance
○ Stored fat in the form of triglyceride in adipose tissue can provide energy to oxidizing tissues such as skelatal muscle and liver as al alternative to glucose
○ Allows circulating glucose to preferentially be available to brain which can't oxidize fat directly
○ In the liver the energy provided by fat oxidation can be used to provide the energy necessary for gluconeogenesis which is an eergy consuming set of reactions
○ In adipose tissue, triglyceride is broken down to fatty acids and glycerol that are released into the circulation
○ Fatty acids are then taken up by tissues like liver and muscle where they are catabolized two carbons at a time in beta-oxidation
§ End-product here is acetyl coA which enters TCA cycle to generate NADH and FADH2
§ These then entery electron transport for ATP production
○ Alternative product of fatty acid breakdown is ketone bodies
§ When insulin is low and counter-regulatory hormones are very high
§ Alternative brain fuel during prolonged fasting and in uncontrolled type 1 diabetes

17

Describe in general how the body handles protein intake and breakdown

• The important aspects of amino acids
○ Structural units of proteins
○ Precursors for other molecules like NT and hormones
○ Substrates for gluconeogenesis
○ Nitrogen carriers
• Urea cycle
○ Amino acids are nitrogen carriers, which is pretty important
○ Pathway involved in disposal of nitrogen derived from metabolism of amino acids is the urea cycle
○ Multi-enzyme pathway that produces urea which enters the blood as blood urea nitrogen or BUN
○ BUN is excreted by kidneys in the form of urine urea nitrogen
○ Plethora of congenital errors in this pathway