Lecture 2b: Fat Metabolism Flashcards
What lipids are transported directly into blood?
- Glycerol
- Short-chain fatty acids
- Medium-chain fatty acids
What lipids are transported through lymph system and then blood?
- Triglycerides
- Cholesterol
- Phospholipids
What is the historical overview of fat and CHO usage?
In the 1900’s high fat diets were promoted, then came fat and CHO diets in the 1910’s and by 1960s CHO popularity grew
High CHO diet increases the stores of what?
Increases muscle glycogen stores
What does increased muscle glycogen stores do for endurance capacity?
Delays onset of fatigue and therefore increases endurance capacity
Trained vs Untrained fat usage during exercise
A trained person will use more fat than an untrained person at a given intensity
High fat diet: Metabolic adaption to capillarisation
Increased capillarisation of muscle (Increased blood flow)
High fat diet: Metabolic adaption to TAG
Increased Intramuscular Triglycerides (IMTG) content
High fat diet: Metabolic adaption to sensitivity
Increased sensitivity of adipose & muscle cells to epinephrine
High fat diet: Metabolic adaption to mitochondria
Increase in number & size of skeletal muscle mitochondria
High fat diet: Metabolic adaption to enzymes
- Increase in enzymes involved in fat transport and metabolism
- Increased activity of oxidative enzymes
What do all the metabolic adaptions to exercise from high fat diets lead to?
increased use of fat as a fuel
What is the adaption to endurance exercise?
Metabolic adaptations to endurance exercise allow a trained individual to use proportionally more fat and less CHO at a given workload.
What is the adaption to high fat diets?
Some research has shown that people adapted to high fat diets undergo similar metabolic changes as those seen with endurance training e.g. Increased intra-muscular TG, changes in enzymes involved in fat oxidation e.g. carnitine palmitoyl transferase.
What is one potential limitation of high CHO diets?
CHO oxidation is increased, reducing fat oxidation
Increasing the proportion of fat used during exercise will increase what?
the rate of CHO utilisation - spare muscle glycogen. Optimising fat usage means you can conserve the CHO store for when intensity is high.
Why do we want to savour CHO stores?
Unlike CHO there is virtually unlimited storage of fat
Why is fat the easiest way to increase energy intake?
It is energy dense:
Per gram of fat = 37kJ
Per gram of CHO = 17kJ
How much ATP does fat produce per gram?
147ATP
How much ATP does CHO produce per gram?
38ATP
How much storage of fat does the body have?
5500 - 10500 g
How much storage of CHO does the body have?
620 - 650 g
Disadvantage of fat as a fuel - oxygen
CHO produces greater ATP yield per unit of oxygen
Disadvantage of fat as a fuel - transportation in blood
Fat = via lymph system
CHO = intestinal abosrbtion
Disadvantage of fat as a fuel - intensity
Cannot be used anaerobically - need oxygen
What are the main storage sites of fat?
As triglycerides in Adipose tissue (5000-10000g)
As intra-muscular triglyceride in muscle (350g)
What are the main storage sites of CHO?
As glycogen in Muscle (500g)
As glycogen in Liver (100-120g)
As glucose in blood plasma (25g)
What happens to fat when you just start exercising?
TAG’s are broken into FFA and glycerol. Glycerol goes to the liver and FFA’s are transported to muscle
What happens once FFA’s reach muscle cells?
Enter the mitochondria to generate ATP
What effects the rate of fat oxidation?
- Exercise intensity
- Exercise duration
- Preceding diet
- Training status
- Plasma FFA (Free Fatty Acids) concentration
- Endogenous and exogenous CHO availability
At rest, what percentage of energy comes from fat?
over 50%
At 25% VO2 max, what percentage of energy comes from fat?
over 80% (fat dominant)
At 65% VO2 max what percent of energy comes from fat?
50% fat, increased IMTG use
At 85% VO2 max, what percent of energy comes from fat?
25% fat, decreased plasma FFA, decreased IMTG use
What is the short term adaption to high fat diets? (1-3 days)
Decreased resting muscle & liver glycogen stores.
Decreased CHO oxidation during subsequent exercise.
Impairment of endurance capacity & performance of prolonged exercise.
What are the short term adaptions to high fat diets (5-10 days)?
- Metabolic adaptations -> increased fat oxidation during exercise
- Compensate for decreased CHO availability
How long does it take for training capacity to be restored on a ketogenic/high fat diet?
within 2-3 weeks, but very variable between athletes
What does fat oxidation look like after 3 weeks on a ketogenic diet?
- Maximal rates of fat oxidation shift from 45% to 70% VO2peak
- Overall fat oxidation rates increase
What is the general consensus of performance on a ketogenic diet?
No difference or worse off
High fat vs High CHO diet for endurance performance
Majority of studies show no difference
What diet do sports nutritionists recommend?
do not recommend a “high carbohydrate diet’ for all athletes, an individualised approach
How should CHO intake be periodised?
should not be static, but periodised across training cycles according to the fuel cost of training load, and importance of training
When should there be high CHO availability?
high intensity /volume /quality / technique
What factors do we need to consider when designing diets? (Individual)
Individual preference: High fat diets = psychological impact
What factors do we need to consider when designing diets? (energy)
Total energy expenditure: Many sporting events require athletes to exercise for many hours over
several days or weeks
What factors do we need to consider when designing diets? (recovery)
Limited time for recovery could mean limited time for glycogen repletion
What should you conduct a meal plan and nutrition principles based on?
- Meeting energy expenditure
- Minimising weight loss
- Optimise Energy : weight ratio of foods
- Nature of event
- Preference
