Energy Balance and Substrate Metabolism Flashcards
Energy Intake
Protein - 15%
Fat - 30-35%
Carbohydrate - 45-50%
Ethanol - 5%
Energy Expenditure
Resting metabolic rate
Diet induced thermogenesis
Physical activity energy expenditure
Energy stores
Fat
Carbohydrate
Energy store - Fat
4.4g in blood
12kg in adipose tissue
300g in muscle - intramuscular triglyceride
> 100,000 kcal
Can be increased to >400,000 kcal
Energy store - Carbohydrate
5g in blood
350-700g in muscle - stored alongside water
100g in liver - can be released in circulation
<3200 kcal
What is leptin?
Hormone secreted by adipocytes and enterocytes
Function of leptin
Regulates energy balance by inhibiting hunger
Acts on cell receptors of the hypothalamus
By injecting leptin, fat mass starts to decrease
Increase in leptin, leads to increase in leptin in order to decrease energy intake
FTO Gene
Fat mass and obesity
Having both alleles predisposes you to carry extra weight
Genetic variations act through energy balance
Methods of measuring intake
Covert
Overt
Covert methods of measuring intake
Researcher weighs food without participants knowing
Overt methods of measuring intake
Researcher weighs food and tells participant
Participant weighed
Participant recall
Participant Food Frequency Questionnaire
Energy density of food
CHO ~ 4 kcal/g
Fat ~ 9 kcal/g
Protein ~ 4 kcal/g
Ethanol ~ 7 kcal/g
Impact of Macronutrient Composition
Alters energy intake independent of energy density
Higher protein intake can suppress appetite and energy intake when in exchange of CHO
Measuring energy expenditure
Laboratory
Free Living
Laboratory methods of measuring energy expenditure
Indirect calorimetry
- Foodstuff
- O2
Direct calorimetry
- Heat
- CO2
- H2O
Free living methods of measuring energy expenditure
Physical activity questionnaires
Doubly labelled water
Pedometers
Accelerometer
Actiheart
Accelerometers and Actiheart
Allow to see difference between intensities of exercise and sedentary time
Doubly labelled water
Ingest 2H218O - heavy water - extra neuron
18O is lost in expired CO2 and water
2H lost in water only
Difference represents average expired CO2 over time period
Strength of doubly labelled water
CO2 production over free-living conditions
Weaknesses of doubly labelled water
Assume RER to determine O2 consumption
Average VCO2 over time
Lean Mass
Primary determinant of resting metabolic rate
Each kg of muscle is responsible for ~13 kcal/d
Metabolic Adaptation
The reduction in RMR during energy restriction
Attenuated when adjusted for body cell mass
Diet Induced Thermogenesis
Fat - 0-3%
Carbohydrate - 5-10%
Protein - 20-30%
Ethanol
- Dehydrogenase pathway ~ 12%
- Microsomal ethanol oxidising system ~ 28%
Physical activity
Most variable component of energy expenditure
Major determinant of muscle mass
Tissue Specific Substrate Metabolism
Muscle biopsy
[6,6-2H2] glucose, stable isotope injection
[U-13C] glucose drink
Muscle biopsy
CHO utilisation
Calculate pre- and post- glycogen levels
[6,6-2H2] glucose, stable isotope injection
Fatty acid kinetics
Liver glucose output
[U-13C] glucose drink
CHO oxidation detected in breath
Measuring liver glycogen use
Liver glycogen concentration decreases with CHO restriction
Increases dramatically with CHO refeeding
Liver biopsy is too dangerous
13C Magnetic Resonance Spectrometry
Exercise Intensity
Primary regulator of substrate metabolism
As intensity increases, oxidation rate of plasma glucose and muscle glycogen increases
Fat oxidation decreases as intensity increases
Most elite events would be mainly reliant on CHO
Factors that influence substrate metabolism
Intensity and duration of exercise
Nutritional status
Training status
Biological sex
Mode of exercise
Environmental temperature and altitude
Wallis et al., 2006
CHO intake suppresses fat oxidation during cycling exercise
Found that women oxidise more fat than men - linked to oestrogen
Areta & Hopkins, 2018
Training status and diet influence muscle glycogen content
Even on low CHO diet, those with a higher VO2max have higher muscle glycogen content
Training status and exercise intensity influence muscle glycogen utilisation
People that are more endurance trained use muscle glycogen more sparingly during moderate to high intensity exercise
Untrained individuals rely more on liver glycogen
Increasing contribution from circulating fuels with exercise duration
Diagram
Regulation of glycogen metabolism
Diagram
Muscle Glycogen Stores
Subsarcolemmal stores
Intermyofibrillar stores
Intramyofibrillar stores
Buchholz & Schoellar, 2004
The substitution of one macronutrient for another has been shown to have a statistically significant effect on energy expenditure part of energy balance equation, mainly high-protein diets.
Hall & Guo, 2017
Meta-analysis of 32 controlled feeding studies with substitution of CHO for fat to review components of energy balance and mechanisms to resist weight loss
Influence of exercise on energy expenditure and body weight
Reductions in energy intake lead to decreased energy expenditure greater than expected due to metabolic adaptation
Energy expenditure (26 kcal/d) and fat loss (16 g/d) were greater with low fat diets
Influence of exercise on energy expenditure and body weight (Hall & Guo, 2017)
Large amounts of exercise are required to result in modest weight loss
Leads to loss of body fat and maintenance of FFM
Individual weight changes are highly variable
Energy expended during exercise is variably compensated by changes in food intake and non-exercise physical activity behaviours
Biomechanical efficiency improvements may decrease cost of exercise, meaning energy expenditure does not progress as exercise does
Jeppesen & Kiens, 2012
Focus on the limitations in fatty acid oxidation in the transition from moderate to high intensity exercise
Inability of fatty acid oxidation to support energy demand during high intensity exercise could be due to:
- Failure of adipose tissue lipolysis
- Limitation in skeletal muscle to oxidise fatty acids
Regulatory candidate for fatty acid oxidation is muscle metabolite carnitine, which is essential for CPT-1 regulation
At high intensity exercise, rapid glycolysis provides mitochondria with excessive acetyl-CoA, which is buffered by free carnitine to form acetylcarnitine
Fall in concentration of free carnitine may reduce CPT-1 activity, so the ability to transport fatty acids into mitochondria
Therefore, rapid glycogen breakdown and glycolysis are suggested to have a major impact on inhibiting fatty acid oxidation
