Carbohydrate Intake and Athletic Performance. How much carbohydrate do athletes need to eat?. What do you need the CHO for?. At rest, brain/nerve cells use about 7 grams/hr= 150g but 50% from gluconeogenesis so need to eat 75g
At rest, brain/nerve cells use about 7 grams/hr= 150g
but 50% from gluconeogenesis so need to eat 75g
Other use (muscle cells, fat cells, etc. using glucose after a meal) plus general “out and about”= 125-150g
Total = about 200-225 grams
30 minutes of easy walking = about 25 grams
45 minutes of moderate running = about 75 grams
60 minutes of hard running = 125 grams
120 minutes of interval running = 200 grams
An average 70 kg male has 1500-1600 kcal of CHO stored in the liver and muscle glycogen and circulating blood glucose.
Muscle: 1200 kcal = 30g
Liver: 320kcal = 80g
Blood Glucose: 20 kcal = 5g
225g + (100-300g) = 325-625g CHO
The daily recommended intake for athletes
is 5-10 g of CHO per kg of body weight.
Ex: 70 kg = 350-700g CHO (1400-2800 kcal)
This is 60% of a 2500 kcal - 5000 kcal diet
(athlete in training).
Glucose, fructose, galactose
Table sugar: sucrose
Milk sugar: lactose
Corn syrup: glucose/fructose
STARCH-plants store extra CHO in the form of starch.
High Glycemic Index CHO = enters the blood from the gut quickly. They are easy to digest/ absorb and enter the circulation within minutes.
Ex: Source g/serving
Low/Mod GI CHO = enter the bloodstream more
slowly. They must be broken down first by
digestive enzymes before being absorbed.
(generally have a higher fiber content).
Choc milk 8oz=25g
60% seems like a lot!
So if CHO is good, is more better?
Is there any evidence in the literature that
increasing CHO consumption will increase
muscle glycogen levels?
And, if you increase your glycogen stores,
does this have any impact on performance?
Supercompensation involves “swelling” muscle glycogen by changing diet and exercise patterns several days before a major competitive event.
2. Modified moderate approach
- depleting glycogen reserves as much as possible through a combination of an extremely long bout of exercise about 7-10 days prior to a major competition, followed by a few days on a very low-CHO diet. Another bout of exercise on the 4th day and then 3 days of a high CHO diet.
2. much as 50% over the usual “full” condition (e.g. from 300 More popular approach is to taper training the week before competition while increasing the %CHO in diet (e.g. from 50-60% up to 70-75%).
Benefits from CHO loading:
(time trial; endurance by 2-3%)
The downside to CHO loading/muscle glycogen supercompensation:
Only good for a one-time ultra distance event (marathon). A cyclist riding over several days would not see benefits...consecutive competition days are not improved with this protocol.
Every gram of CHO is stored with 3g of water. This means that the storage of 500g of CHO is accompanied by a water weight gain of approximately 2kg. This would not be good for sports where an increase in body mass is not desirable.
3-5 hours: this is usually breakfast supercompensation:
Large meal to replenish liver glycogen
Increase muscle glycogen stores
Remember that the liver glycogen is used to:
Maintain blood glucose levels (it’s the brain food)
It’s decreased after an overnight fast.
It’s decreased by 50% after an hour of exercise at 75% VO2max.CHO intake before exerciseGoal: maxmize exercise performance
Common belief: ingesting High GI CHO right before exercise will create rebound hypoglycemia and decrease performance.
Insulin release stimulated by glucose promotes skeletal muscle glucose uptake. Exercise (muscle contractions) also stimulate glucose uptake...both are working...
There is little evidence to support this hypothesis that performance is decreased...
However, two strategies are widely used to prevent rebound hypoglycemia in athletes.
“once on gatorade-stay on gatorade”
CHO consumption during exercise >45min can improve performance.
How much should I consume? performance is decreased...
What should I drink?
glucose polymer (gatorade=good)
galactose,fructose-not so good, must first be converted to glucose by the liver to be used as a substrate.
The delivery rate from the gut to the muscle tissue is 1.0g/min, as intensity increases blood flow to the digestive system decreases and there is a greater reliance on muscle glycogen as a fuel source.
Choose drinks ranging from 4-8% CHO. Drinks with too much CHO (coke has 11.25% CHO) will not be absorbed as efficiently and could cause stomach upset.
Remember that CHO replacement during exercise is not generally needed for activities lasting less than 90 minutes.
GOAL: To replenish muscle glycogen
The rate of glycogen synthesis depends on glucose transport to the muscle and the enzymes involved in glycogen synthesis.
- GLUT 4 (transporters)
- glycogen synthase
There are two phases of muscle glycogen replenishment after post-exercise CHO consumption:
Rapid (not dependent on insulin-but enhanced)
Slow (>3hrs, insulin dependent)
Once CHO needs are met, the effect of protein supplementation does not enhance muscle glycogen storage.
Glycogen synthesis relative to control
The key to optimal recover is to create a hormonal environment that is anabolic and provides the necessary raw materials.
Eating foods high in CHO provides glucose and also stimulates a large insulin response that facilitates entry of glucose into cells and its storage as glycogen.
Maximizing the amount of glycogen stored depends on both the quantity of CHO and the insulin response: in the short-term (first 2-6 hours) there does appear to be an advantage to consuming simple sugars rather than complex CHO because the insulin response is greater.