Energy balance Flashcards
What is energy Balance
- Energy balance is the relationship between Total Daily Energy Intake (TDEI) and Total Daily Energy Expenditure (TDEE)
- A balance between these determines if the body stores energy (positive balance), uses stored energy (negative balance) or remains stable
Two components of Energy Balance
- Total daily energy intake (TDEI)
- Total daily energy expenditiure (TDEE)
What are the components of TDEE?
○ Resting Metabolic Rate (RMR)
○ Thermic Effect of Food (TEF)
○ Energy Expenditure of Activity (EEA)
What does TDEI refer to?
TDEI is the total energy (in kcals) from food ingested and absorbed.
- It is important to note that the calories ingested are not always the same as the calories available for human use
How is the energy content of food measured, and what is the unit of measurement?
○ The energy content of food is measured in calories (cal), with kilocalories (kcal) being the common unit (1 kcal = 1000 cal).
○ A kcal is the energy needed to raise the temperature of 1kg of water by 1°C.
○ A direct calorimeter (bomb calorimeter) burns food to measure its energy content
○ However, the energy available for humans is not always the same as the energy measured with a bomb calorimeter.
○ Software (e.g. ESHA, My Fitness Pal) is often used to estimate available energy, although this has limitations
How is the energy in food measured or estimated?
- Direct calorimetery
- burn food in the bomb calorimeter and see the increase in water temperature
What is RMR? How is it measured?
- RMR is the energy needed to sustain basic life functions at rest
- Measured through direct calorimetry (heat production), indirect calorimetry (analysis of expired gases), or prediction formulas
- RMR is measured under less restricted conditions than BMR
RMR= resting metabolic rate
What is BMR and how is it measured?
- BMR is the basal metabolic rate. It is the number of calories your body needs to accomplish its most basic (basal) life-sustaining functions
- Measurements are taken in a darkened room upon waking after 8 hours of sleep, 12 hours of fasting, with the subject resting in a reclined position
BMR is taken under very strict conditons
What is Thermic Effect of Food (TEF) or Diet-induced thermogenesis (DIT)?
- the energy needed to digest, absorb and store nutrients. it typically accounts for about 10% of TDEE
- The type of macronutrient influences TEF, with protein requiring the most energy
- 50-75% of DIT is obligatory, the rest can be blocked with adrenergic blockade
What is the Energy Expenditure of Activity (EEA)
- The energy needed for all activities involving skeletal muscle
- includes TEE (thermic effect of exercise) and NEAT (non-exercise activity thermogenesis)
EEA is the most variable component of TDEE
What is NEAT?
- Non-exercise activity thermogenesis. It is the energy expanded for everything that is not sleeping, eating or sports/exercise-like activities
- It can be a very variable component of TDEE
What is a direct calorimeter?
- A device that burns food to measure its energy content.
- Using a calorimeter, which would be a sealed room that controls and measures O2 used and CO2 produced and temperature to acess energy production
What is metabolizable energy?
The amount of energy available for the human body to use from ingested food
What is the Atwater factor?
- A system that allocates energy values to food based on the heat of combustion, corrected for losses in digestion, absorption and excretion
- Atwater factors represent the total amount of digestible energy in an energy source, expressed as kcal/g.
What are the Atwater factors for carbohydrates (CHO), fat, and protein (PRO) & ethanol?
- CHO: 4 kcal/g,
- Fat: 9 kcal/g,
- PRO: 4 kcal/g
- Ethanol: 7 kcal/g
What is subtracted from CHO before calculating calories?
Dietary fiber
How is the coefficient of digestibility calculated?
Coefficient of digestibility= Energy available / Energy of combustion
Are the coefficients of digestibility for CHO and fats typically high or low?
High, typically >90%
Is the coefficient of digestibility for protein higher or lower than for CHO and fats?
Lower
What factors can lower energy availability?
- 15-19% of protein is nitrogen, which is excreted as urea and doesn’t provide energy
- Insoluble fiber, which is not absorbed
- High levels of fiber
Approximately what percentage of potential energy is lost in protein?
20%
How many kcals per gram does insoluble fiber provide?
0 kcals/g
How many kcals per gram does soluble fiber provide (in Canada)?
2 kcal/g or lower
Why are Atwater specific factors not used by the general public?
Because they are too complex
What are some limitations of energy availability estimations?
Energy availability may differ from Atwater factors, mixed meals may not equal the sum of their parts, dietary fiber affects digestibility and gut microbiota
What affects food metabolism?
Gut microbiota
What is the oxidative hierarchy?
- the order in which the body prioritizes fuel combustion, based on storage capacity and survival
- An indicator of a fuel’s dominance within metabolic pathways
What is the order of fuel combustion in the oxidative hierarchy?
- Alcohol; burned first because it cannot be stored
- CHO; are next due to limited storage and obligatory requirements (e.g., the brain).
- Protein; limited storage and an obligatory requirement
- Fat; a small obligatory requirement and large storage capacity
Why is alcohol burned first in the oxidative hierarchy?
Because there is no capacity for storage
What does alcohol consumption suppress?
Other fuel oxidation, especially fat
What happens to excess protein or CHO consumption?
It results in an autoregulatory increase in their oxidation
What controls fat oxidation?
The ingestion of other macronutrients, such as CHO
What is the body’s response to excess macronutrient intake?
◦ Excess protein or carbohydrates: results in an autoregulatory increase in their oxidation.
◦ Excess fat: is efficiently stored as body fat (adipocytes), with minimal effect on fat oxidation
Does the body care about the source of calories (fat vs. CHO) in energy balance?
When in energy balance, no! The body does not care about the source of calories. Energy expenditure is similar across a range of fat and carbohydrate intakes.
Fat oxidation is suppressed as CHO oxidation is increased and vice versa.
However, the respiratory quotient (RQ) changes to reflect which macronutrients are being metabolized
Does the body care about the source of calories (fat vs. CHO) when NOT in energy balance?
Yes, When over/underfed CHO, CHO metabolism changes to a similar extent.
High CHO intake suppresses fat oxidation, and low CHO intake increases fat oxidation.
When fat intake is manipulated there is minimal change to fat metabolism. The system is effectively blind to differences in fat intake
What changes when macronutrients are metabolized in energy balance?
Respiratory Quotient (RQ)
RQ reflects the gas exchange ratio at the cellular level
What happens to CHO metabolism when over/underfed CHO?
It changes to almost the same extent
What happens to fat metabolism when over/underfed fat?
Minimal response of fat metabolism. The system is effectively blind to differences in fat intake
Is fat storage efficient?
Yes. Fat is very efficiently stored as body fat
the macronutrient source matters in terms of storage
What is the most variable component of TDEE?
EEA
What is the approximate percentage of TDEE for RMR?
~60-75%
What is the approximate percentage of TDEE for TEF?
~ 10%
What is the approximate percentage of TDEE for EEA?
~ 15-30+ %
What are examples of ways to measure TDEE?
Doubly Labeled Water, Calorimetric Chamber, and measuring or estimating components (RMR, TEF, EEA
What is Doubly Labeled Water?
Water in which both hydrogen and oxygen have been partly or completely replaced with uncommon isotopes for tracing purposes.
Used to measure TDEE
How is Doubly Labeled Water used to measure EE?
By measuring the difference in the excretion rates of oxygen-18 and deuterium
What are the differences between RMR and BMR measurement?
BMR is measured under more restrictive conditions like darkened room and after 12 hours fasting whereas RMR is measured under less restrictive conditions
What are the conditions for measuring RMR?
Overnight fast, subject awake, controlled phase of menstrual cycle, abstinence from exercise (12 hr), resting in a supine position, thermoneutral conditions
What is indirect calorimetry?
- Measuring expired gases to determine metabolism
- energy expenditure is calculated from measuring the amounts of O2 used and CO2 produced using open circut spirometry
What is adaptive thermogenesis?
Heat production, which is made up of obligatory and facultative thermogenesis
What is obligatory thermogenesis?
The energy required to digest, absorb, and metabolize nutrients (eg. BMR)
What is facultative thermogenesis?
A specialized form of thermogenesis activated as a cold defense mechanism to maintain body temperature
What activates facultative thermogenesis?
Shivering (skeletal muscle) and brown fat metabolism
What happens to RMR with weight loss?
RMR decreases linearly with weight loss but often drops lower than predicted. Repetitive weight loss can cause a significant drop in RMR
Is RMR linearly related to body weight?
Yes, if you lose 10lbs, expect a similar decrease in RMR
What is the effect of acute and chronic exercise on RMR?
Research shows inconsistent results. Acute exercise may increase RMR due to Excess Post-exercise Oxygen Consumption (EPOC) which may last up to 48 hours
What happens to RMR during diet-induced weight loss?
RMR can drop more than expected based on the amount of tissue lost, especially with severe, repetitive weight loss
What does increased FFM mean for RMR?
Greater resting metabolic rate
What is EPOC and how does it affect RMR
- Excess Post-exercise Oxygen Consumption
- The increased energy expenditure (EE) that occurs mostly in the first few hours after exercise.
- It can lead to a ~5% increase in RMR
What influences DIT?
Type of macronutrients (protein requires the most energy), and exercise
Which macronutrient requires the most energy for DIT?
Protein
What percentage of DIT is thought to be obligatory?
50-75%
What is the effect of increasing age on DIT?
Lowers DIT
What is a MET?
A measure of the metabolic rate during physical activity (1 MET = 3.5 mLO2 / kg / min)
Is the energy cost of PA over or underestimated by METS?
understimated
How does diet affect TEF?
TEF is proportional to the energy and protein content of a meal. Protein requires the most energy to process
What is the Physical Activity Level (PAL)?
Total Energy Expenditure divided by Basal Metabolic Rate
What are some factors that affect EEA?
Frequency, Intensity, Time, and Type of activity
What is the set point theory?
The theory that the body has an internal control mechanism that regulates metabolism to maintain a certain level of body fat. It hypothesizes that there is a target level for body weight
Why is the set point theory unlikely?
- It does not explain why the world’s set points have increased over the last 50 years.
- It is contradicted by studies showing that starvation and subsequent refeeding results in even higher body and fat mass
What is the settling point theory?
The idea that weight loss and gain are more related to patterns of diet and physical activity that people “settle” into as habits based on the interaction of their genetic dispositions, learning, and environmental cues to behavior
What is the steady state theory?
The theory that an increase in inflow will equal an increase in outflow. Perturbations in energy intake or expenditure result in compensatory changes in these components
What is hunger?
Sensations that promote food consumption
What is satiation?
sensations that goven meal size and duration
What is satiety?
Sensations that determine the intermeal period of fasting
What are orexigenic and anorexigenic substances?
Orexigenic: Stimulating effect on the appetite (e.g., Ghrelin)
Anorexigenic: Causing loss of appetite (e.g., Leptin)
How do we measure appetite?
Brain imaging, biomarkers, food intake, and questionnaires (e.g., Visual Analogue Scales)
What is the role of the brain in regulating EI and EE?
The brain integrates signals from meals and fat stores to regulate EI and EE to maintain stable fat stores
What happens to the rewarding properties of food when you are starving?
They increase, and satiety signals decrease
What happens to the rewarding properties of food when you are overfeeding?
They are inhibited, while meal-induced satiety is enhanced
What are peripheral signals in energy balance regulation?
Leptin, insulin, ghrelin, PYY, CCK, GLP-1
What is leptin?
A protein synthesized and secreted from adipose tissue
Where is leptin secreted?
adipose tissues
What is the relationship between leptin and fat mass?
[Leptin] is proportional to fat mass (+ve
What is the function of leptin?
decrease in food intake and weight loss (anorexigenic)
Most obese individuals are leptin resistant
What is the relationship between Leptin and obesity?
-Most obese individuals are leptin resistant not deficient
- When a leptin deficient individual is treated with leptin, they lose weight
What is insulin?
- A peptide hormone secreted by the β-cells of the pancreas in response to a rise in glucose load
- It reduces appetite or increases EE
- It’s less effective in obese or type 2 diabetes (insulin-resistant)
Where is insulin secreted?
By the β-cells of the pancreas
What is the role of insulin in appetite?
In the periphery it increases appetite, in the brain it reduces it
What is ghrelin?
A peptide synthesized predominantly in the stomach, which stimulates growth hormone (GH), increases food intake (orexigenic), levels rise with fasting and fall with feeding
What is Peptide YY (PYY)?
- A peptide secreted from the small and large intestine after feeding that leads to reduced food intake
- Individuals with obesity may be resistant to PYY
What is Glucagon-like-peptide-1 (GLP-1)
A peptide co-secreted with PYY in response to nutrients in the gut. It inhibits feeding, enhances insulin secretion, and suppresses glucagon after a meal
What is Cholecystokinin (CCK)
A gut hormone that inhibits feeding, and stimulates digestion of fat. It is secreted by the duodenum
What is Low Energy Availability (LEA)
- The amount of dietary energy remaining after exercise, available for other physiological functions such as growth, muscle recovery, and homeostasis.
- It is associated with the majority of consequences of Relative Energy Deficiency in Sport (RED-S)
Why is energy availability important in sport?
Sufficient energy availability and quality of nutrition are essential to support health and desired adaptations
How does LEA happen?
Can occur intentionally, due to body weight concerns, or unintentionally, due to poor biological regulation matching energy intake to expenditure. It can also happen at both upper and lower limits of EE
What are the signs and symptoms of LEA?
Reduced training capacity, repeated injury or illness, delayed or prolonged recovery times, change in mood state, failure to lose weight, reduced or low bone density, reduced libido, cessation or disruption in menstrual cycle, excessive fatigue
