Introduction to Energy Balance Flashcards
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
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
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
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
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%
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
You need to know how the body handles what three nutrients like the back of your hand?
- Glucose
- Fatty acids
- Amino acids
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
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
What is the most accurate way of measuring body composition?
- DEXA
* Dual energy x-ray absorptiometry
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
What are the main forms of energy currency in cells?
- ATP
* And NADH, NADPH, FADH2 to a lesser extent
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?
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
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
