Carbohydrate and Fat

Question 1

Carbohydrate in the body

Answer 1

• glycogen in liver: 80-110g
• glycogen in muscle: 300-600g
• glucose: 4-6g

Question 2

carbohydrate function

Answer 2

• energy
• central nervous system
• physical activity
• fibre: health benefits

Question 3

influence of exercise intensity

Answer 3

• increase in muscle glycogen use
• stable plasma FFA
• slight increase in plasma glucose

Question 4

liver (hepatic) glucose output and blood glucose

Answer 4

• exercise increases liver glucose output in a intensity dependent manner
• closer matching between muscle glucose uptake and liver glucose output

Question 5

carbohydrate utilisation during exercise

Answer 5

• exercise increases carbohydrate oxidation in an intensity dependent manner
• this involves:
  
  • increased liver glucose output (to equal muscle glucose uptake)
  • increased muscle glycogen breakdown

Question 6

muscle glycogen and fatigue

Answer 6

‘at high relative workloads, glycogen stores in exercising muscle is a decisive factor for maximal work time

Question 7

fatigue during prolonged strenuous exercise

Answer 7

• fatigue strongly correlated with carbohydrate depletion
  
  • muscle glycogen depletion
  • hypoglycemia reflecting liver glycogen depletion
• evidence that diet (carbohydrate feeding) can affect these processes
  
  • carbohydrate loading to increase muscle glycogen
  • carbohydrate during exercise to maintain blood glucose

Question 8

high carb, low carb… flexi carb

Answer 8

• carbohydrate intake can be flexible, depending on training and competition needs
  
  • periodised approach
  • fuel for the work required
• the second thing to understand is that daily carbohydrate recommendations are typically periodised to energy and carbohydrate demands

Question 9

acute fuelling strategies

Answer 9

promoting high carbohydrate availability to promote optimal performance in key training sessions or competition

Question 10

daily carbohydrate intake goals for athletes

Answer 10

• light: 3-5g/kg/d
• moderate: 5-7g/kg/d
• high: 6-10g/kg/d
• very high: 8-12g/kg/d

Question 11

day/days leading up to the event

Answer 11

• general fuelling up - prep for events lasting <90 min exercise - 7-12g/kg/d as per daily daily fuel needs
• carb-loading - prep for event >90 min in sustained, intermittent exercise - 10-12g/kg/d for 36-48 hours pre-event

Question 12

day of the event

Answer 12

• the main goal here is around ensuring liver glycogen stores are high ready for performance
• pre-event fuelling - exercise lasting >60 mins - 1-4g/kg body mass, consumed 1-4 hours before exercise

Question 13

recommended carbohydrate intake for athletes before exercise

Answer 13

• 4 hours prior = 4g/kg
• 3 hours prior = 3g/kg
• 2 hours prior = 2g/kg
• 1 hour prior = 1g/kg
• e.g. toast, bagels, porridge, cereal, rice, scotch pancakes, cereal bars, bananas

Question 14

after exercise (before the next training session or competition)

Answer 14

priority to replenish muscle glycogen after training/competition

Question 15

what about fat?

Answer 15

• fat availability for energy production not limited even in leanest of athletes
• fat is a fuel source during low-to-moderate intensity aerobic exercisef

Question 16

fat recommendations for sport

Answer 16

• fats have many important functions in the body and should not be excluded from the diet
• daily fat intake: 20-35% of total energy intake
• proportion of saturated fat limited to less than 10% of energy intake
• for weight loss/body composition changes, chronic fat intake <20% of energy intake discourages

Question 17

functions of fat

Answer 17

• fuel source
• protection of vital organs
• cell membrane constituents
• precursors of bile, hormones and steroids
• essential fatty acids and fat-soluble vitamin intake
• palatability

Question 18

fat adaptation, carbohydrate restoration studies

Answer 18

• fat adaptation:
  
  • increased fat oxidation
  • decreased carbohydrate oxidation
  • spared muscle glycogen
• fat adaptation impairs high-intensity exercise performance

Question 19

ketogenic diets and keto-adaptations

Answer 19

• <50g carbohydrate/day, fat intakes >70-80% energy
  
  • ~15% or 1.5g/kg/d protein (not >25%)
  • ensure adequate sodium/potassium
• at least 2-3 weeks adaptation, keto-adaptation
• elevated blood levels of ketones and tissue adaptations to enhance their use as fuel
• increase use of fat as muscle fuel

Question 20

rethinking fat as a fuel for endurance exercise

Answer 20

• fatigue due to reduced CHO availability and inability to use alternate lipid sources
• lowering CHO intake and increasing fat intake will induce ketosis (>0.5mmol/L) over several weeks
• keto-adaptation ensures stable fuel source for exercising muscle (and brain) in the face of low CHO availability
• shift to fats and ketones as primary fuels could benefit endurance performance