Carbohydrate and Fat Flashcards
Carbohydrate in the body
- glycogen in liver: 80-110g
- glycogen in muscle: 300-600g
- glucose: 4-6g
carbohydrate function
- energy
- central nervous system
- physical activity
- fibre: health benefits
influence of exercise intensity
- increase in muscle glycogen use
- stable plasma FFA
- slight increase in plasma glucose
liver (hepatic) glucose output and blood glucose
- exercise increases liver glucose output in a intensity dependent manner
- closer matching between muscle glucose uptake and liver glucose output
carbohydrate utilisation during exercise
- exercise increases carbohydrate oxidation in an intensity dependent manner
- this involves:
- increased liver glucose output (to equal muscle glucose uptake)
- increased muscle glycogen breakdown
muscle glycogen and fatigue
‘at high relative workloads, glycogen stores in exercising muscle is a decisive factor for maximal work time
fatigue during prolonged strenuous exercise
- 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
high carb, low carb… flexi carb
- 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
acute fuelling strategies
promoting high carbohydrate availability to promote optimal performance in key training sessions or competition
daily carbohydrate intake goals for athletes
- light: 3-5g/kg/d
- moderate: 5-7g/kg/d
- high: 6-10g/kg/d
- very high: 8-12g/kg/d
day/days leading up to the event
- 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
day of the event
- 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
recommended carbohydrate intake for athletes before exercise
- 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
after exercise (before the next training session or competition)
priority to replenish muscle glycogen after training/competition
what about fat?
- fat availability for energy production not limited even in leanest of athletes
- fat is a fuel source during low-to-moderate intensity aerobic exercisef
fat recommendations for sport
- 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
functions of fat
- fuel source
- protection of vital organs
- cell membrane constituents
- precursors of bile, hormones and steroids
- essential fatty acids and fat-soluble vitamin intake
- palatability
fat adaptation, carbohydrate restoration studies
- fat adaptation:
- increased fat oxidation
- decreased carbohydrate oxidation
- spared muscle glycogen
- fat adaptation impairs high-intensity exercise performance
ketogenic diets and keto-adaptations
- <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
rethinking fat as a fuel for endurance exercise
- 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
