Lecture 6: Carbohydrates Flashcards
What is anaerobic glycolysis?
the process of breaking down glucose (carbohydrate) to release energy to phosphorylate ADP and form ATP
When is anaerobic glycolysis used?
without oxygen, rapidly producing ATP for short-term, high-intensity activities
What is glucose broken down into during anaerobic glycolysis?
pyruvate and lactic acid
What is the final product of anaerobic glycolysis?
Lactate + H+
Where is glycogen stored?
in muscle or liver
What is glycogen?
the stored form of glucose
How many ATP is produced during anaerobic glycolysis from glucose?
2 ATP
How many ATP is produced during anaerobic glycolysis from glycogen?
3 ATP
What is aerobic metabolism?
the process by which cells produce energy (ATP) through the oxidative phosphorylation of glucose, fatty acids, or amino acids in the presence of oxygen
What is oxidative phosphorylation?
the process by which ATP is produced in the mitochondria through the transfer of electrons from NADH and FADH2 to oxygen
Does aerobic metabolism stop?
continuous supply of ATP as long as O2 is available
Where does aerobic metabolism occur?
Mitochondria
What are the 3 phases of aerobic metabolism?
- Preparation
- Krebs cycle/TCA cycle
- Electron transport chain (ETC)
What happens in the Krebs cycle/TCA cycle?
oxidises, removes, electrons
What happens during the ETC?
electrons undergo a number of reactions releasing energy to rephosphorylate ADP to ATP
How many ATP does aerobic metabolism produce?
30-32 ATP
What type of exercise is CHO one of our most important fuels for?
endurance exercise - anything over an hour, energy is generally coming from CHO sources
Where does carbohydrate digestion begin?
In the mouth
What happens to CHO in the mouth?
Salivary a-amylase hydrolyses dietary starch
Where does CHO go after the mouth?
The stomach
What happens to CHO in the stomach?
The acidity of the stomach temporarily inhibits a-amylase and stops carbohydrate digestion
Where does CHO go after the stomach?
The small intestine
Is the small intestine acidic?
No
How is the small intestine neutralized?
Bicarbonate secretion from the pancreas neutralises the stomach contents and pancreatic a-amylase continues to digest starch
How are CHO broken down into smaller molecules in the small intestine?
Several disaccharide enzymes breakdown disaccharides in the brush border of the small intestine producing monosaccharides
What are monosaccharides?
glucose, fructose, galactose
Where are CHO absorbed?
The small intestine
How is glucose absorbed in the small intestine?
via a sodium glucose transporter (SGLT-1)
How is fructose absorbed in the small intestine?
via the transporter GLUT5
How are glucose and fructose transported across the basolateral membrane?
via the transporter GLUT-2
After being transported out of the small intestine where do glucose and fructose go?
Transported to the liver where fructose is removed from the circulation
What is glycogenesis?
the process by which glucose molecules are converted into glycogen for storage in the liver and muscle cells
What is insulin?
a hormone produced by the pancreas that helps regulate blood glucose levels
How does insulin regulate blood glucose levels?
by facilitating the uptake of glucose into cells and promoting its storage as glycogen in the liver and muscles
What does CHO ingestion stimulate?
the release of insulin from the pancreas
What does insulin stimulate?
GLUT-4 translocation to muscle membrane
What is glucose-6-phosphate?
an important intermediate in glycogenesis
What does glucose-6-phosphate stimulate?
the production of glycogen
What is the total carbohydrate store for an 80kg male?
approx. 450-500g
What are carbohydrate stores affected by?
fasting, exercise and diet
What is the biggest store of CHO?
Muscle
What is the smallest store of CHO?
Blood
What is the second biggest store of CHO?
Liver
What is CHO a fuel for?
muscle and brain during exercise
What do low levels of CHO cause?
fatigue and reduced performance
What is the daily CHO recommendation for very light training?
3-5g/kg/d
What is the daily CHO recommendation for moderate/low intensity training (1hr/d)?
5-7g/kg/d
What is the daily CHO recommendation for moderate to heavy training (1-3hr/d)?
6-10g/kg/d
What is the daily CHO recommendation for extreme exercise (>4-5hr/d)?
8-12g/kg/d
Do athletes generally meet their CHO needs?
No, very few do
What factors cause suboptimal intakes of CHO?
- Restricted energy intake
- Inadequate skills
- Culture
- Availability
- GI discomfort
- Fad Diets
- Chaotic lifestyle/travel
What is the first step in changing future behaviour?
understanding current behaviour
What is the stigma around CHO?
that if you eat a high carb diet you will get fat
What happens when insufficient CHO is ingested?
Progressive decrease in muscle glycogen which don’t get replaced
How do you replace glycogen stores?
With a high CHO diet
How does a high CHO effect training?
Maintain performance better and have a higher mood state during intensified training
Can CHO before exercise improve performance?
Yes, even if you have an overall high CHO diet, having right before/morning of CHO before exercise improves performance - this is because even when we are sleeping our glycogen stores are being used
Why can we not endlessly consume CHO to improve performance?
GI stress
When is GI stress common?
during long distance races
Is GI stress consistent between different athletes?
No, highly individual, perhaps genetically determined
What could GI stress be related to the intake of?
- highly concentrated CHO solutions
- hyperosmotic drinks
- intake of fibre, fat and protein
What is CHO/glycogen loading?
Maximizing the amount of glycogen stored in muscles and liver
What is the downside of glycogen loading?
When we store glycogen in our muscles we also store water which can cause water retention in our muscles which makes the athletes feel very heavy
What are the positive impacts of CHO loading?
improve performance approx. 2-3%
How much CHO do you need to consume for loading?
can vary from around 10-12g/kg/d depending on the athlete and their activity
What are pre-event meal considerations?
- Time of day event is
- Length of event
- Nerves
- Location
- Past experience
- GI stress
What are the aims of pre-exercise fueling?
- Prevent muscle and liver glycogen depletion
- Prevent hypoglycaemia
- Prevent GI stress
What should dehydration be limited to during exercise?
limit to less than 2% BM loss
The longer the exercise…
the more CHO needed per hour
How much glucose can you utilize per hour?
about 60-90g, if you are consuming more then you need to increase the fructose
Can the gut be trained?
By gradually increasing intakes the gut is able to increase uptake with exposure
How do we restore muscle and liver glycogen levels to pre-exercise levels?
CHO intake of 1/5g/kg/d during first 30 mins and again every 2h for 4 to 6h
What considerations need to be taken when restoring CHO stores?
- Time to next session
- Intensity of session
- Demands of next session
- GI tolerance
- Logistics
Why is it important to re-fuel directly after exercise?
first few hours are most important as the muscle is most receptive to storing glycogen
What is oestrogen?
a group of steroid hormones responsible for regulate the development and function of the female reproductive system - present in smaller amounts in males
What are the main types of oestrogen?
oestrone, oestradiol, oestriol
What functions does oestrogen have?
important for muscle mass, inhibits bone resorption
What is progesterone?
a steroid hormone that plays a crucial role in the menstrual cycle and pregnancy - present in smaller amounts in males
What functions does progesterone have?
increases muscle protein synthesis rates, stimulates osteoblasts
What is a eumenorrheic cycle?
a regular menstrual cycle characterized by predictable and consistent patterns
What percentage of female athletes are eumenorrheic?
67-91%
What does estrogen increase during exercise?
fatty acids availability and promote lipid oxidation
What does progesterone limit during exercise?
fat oxidation
Why is it important to individualise according to an athletes menstrual cycle?
there will be an increase and decrease in CHO and fat absorption over the month
The menstrual cycle effects are seen to a greater extent in…
those with PMS, and recreational athletes
How does hormonal contraception affect endurance exercise?
Elevated plasma estrogen concentrations increase the reliance on fat as an energy source during endurance exercise
What is the best way to prescribe dietary CHO intake based on the menstrual cycle?
There is insufficient high quality evidence
How much water retention is there per gram of glycogen?
Approx. 3g water per gram of glycogen
In order for an athlete to actually oxidise 90g per hour they should likely ingest…
100-120g/h, owing to the fact that oxidation efficiency is not uniform
