Questions and Answers
What is the percentage of CHO in a 14g/240g fluid?
What is the process by which plants form carbohydrates from the energy of the sun?
Why is a cola beverage not a good sports drink?
How much of a 6% CHO-containing sports drink does the cross country skier need to consume each hour to obtain 30g of CHO?
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What is the recommended daily intake of carbohydrates for adults and children?
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Who may benefit from CHO supplementation before exercise?
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What is the main component of sports drinks?
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What is the effect of consuming CHO during prolonged exercise?
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What is the percentage of daily energy intake recommended to come from carbohydrates?
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When should simple sugar be taken before exercise?
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What is the percentage of total calories that should come from added sugars?
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What is the primary function of carbohydrates in the body?
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Which of the following is an example of a polysaccharide?
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What is the percentage of total calories that should come from carbohydrates for athletes engaged in prolonged heavy exercise?
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What may limit performance in intermittent, anaerobic type exercise tasks?
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What is the recommended amount of CHO to be consumed 4 hours prior to performance?
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What is a contributing factor to fatigue in prolonged endurance exercises?
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What happens to BCAA in the blood after prolonged exercise bouts?
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How often should CHO feedings be consumed during exercise?
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What is the recommended concentration of CHO in sports drinks?
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What is the result of an increase in Trp:BCAA ratio in the brain?
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How much CHO is recommended to be consumed during ultraendurance events?
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How soon after ingestion can exogenous CHO be used as an energy source?
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What is the recommended amount of glucose polymer to be consumed within 10 minutes of the start of exercise?
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What is the peak time of use of exogenous CHO after ingestion?
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What is a limitation of glucose ingestion in preventing fatigue?
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What is the effect of consuming CHO both before and during exercise?
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How much CHO is recommended to be consumed during maximal exercise lasting less than 45 minutes?
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What is the approximate maximum amount of energy derived from exogenous carbohydrate per minute?
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Is there a difference between the different types of CHO to enhance endurance performance?
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What is the daily recommended intake of AI of fibers for men over age 50?
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Where does the majority of absorption occur in the digestive tract?
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What is the function of salivary amylase in the digestion process?
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What happens to insoluble fiber in the digestive process?
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What is the effect of high concentrations of simple sugars on the intestine?
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What is the fate of most of the absorbed CHO and the majority of the absorbed fru and gal?
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What is the effect of lactose on some athletes?
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What happens to glucose after it is absorbed into the bloodstream?
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Study Notes
Carbohydrates: The Main Energy Food
- Carbohydrates are formed when the energy from the sun is harnessed in plants through the process of photosynthesis.
- There are different types of dietary carbohydrates, including:
- Monosaccharides (e.g. glucose, fructose, galactose)
- Disaccharides (e.g. sucrose, lactose, maltose)
- Polysaccharides (e.g. starch, glycogen, cellulose)
- Other types of carbohydrates (e.g. sorbitol, polydextrin, B-glucans)
Common Foods High in Carbohydrates
- Sports drinks (e.g. Gatorade) contain 6-8% carbohydrates in the form of glucose, fructose, sucrose, and/or glucose polymers.
- Sports gels (e.g. Power Gel, ReLode) contain the same types of carbohydrates as sports drinks, but in a more solid form.
- Sports bars contain 20-45g of carbohydrates.
- Energy drinks contain 30-50g of carbohydrates per 8 oz serving.
Carbohydrate Requirements
- The recommended daily intake of carbohydrates is 130g for adults and children, with the brain accounting for 50% of total body glucose utilization.
- The acceptable macronutrient distribution range (AMDR) for carbohydrates is 45-65% of daily energy intake.
- The daily value (DV) on food labels is based on a recommendation of 60% of caloric intake from carbohydrates.
- No more than 25% of total calories should come from added sugars.
- The adequate intake (AI) of fiber is 38g/d for men up to age 50, 30g/d for men over age 50, 25g/d for women up to age 50, and 21g/d for women over age 50.
Metabolism and Function
- Digestion is the process by which food is broken down mechanically and chemically in the digestive tract and converted into absorbable forms.
- Absorption occurs in the stomach and large intestine, but the majority occurs in the small intestine through passive diffusion and facilitated diffusion.
- Some starch is broken down to maltose in the mouth by salivary amylase.
- Salivary amylase is inactivated by strong acid in the stomach.
- Pancreatic amylase breaks down starch into maltose in the small intestine.
- Enzymes in the wall of the small intestine break down disaccharides into monosaccharides.
- Glucose, fructose, and galactose are absorbed into the blood to be taken to the liver by the portal vein.
- Some soluble fiber is fermented into various acids and gases by bacteria in the large intestine.
- Insoluble fiber escapes digestion and is excreted in the feces.
Carbohydrate Digestion and Absorption
- The composition of dietary carbohydrates may influence delivery into the body.
- Certain dietary practices may predispose individuals to GI distress, which can compromise exercise performance.
- Foods containing carbohydrates and sodium enhance the absorption of water.
What Happens to Carbohydrates After Absorption
- Most of the absorbed carbohydrates are converted to glucose (blood sugar).
- Low levels of glucose in the white, fast-twitch IIb muscle fibers may limit performance in intermittent, anaerobic type exercise tasks.
- Hypoglycemia and low glucose in red muscle fiber type are contributing factors to fatigue in prolonged endurance exercises.
Low Endogenous Carbohydrate Levels and Central Fatigue Hypothesis
- Prolonged exercise bouts lead to low muscle glucose and hypoglycemia, which can cause gluconeogenesis from muscle protein.
- Decreased release of branched-chain amino acids (BCAAs) from the liver or increased uptake by muscle leads to decreased blood BCAA concentration, causing fatigue.
- An increase in tryptophan concentration and competition with BCAAs for similar receptors that facilitate their entry into the brain leads to an increase in serotonin formation, causing fatigue sensation.
Effect of Carbohydrate Ingestion on Physical Performance
- Exogenous carbohydrates may be used as an energy source within 5-10 minutes of ingestion.
- The peak of use occurs at 75-90 minutes after ingestion.
- Possible fatigue-delaying mechanisms include:
- Maintenance of blood glucose levels
- Reduction of psychological effort by reducing the rate of perceived exertion
- Sparing of muscle glycogen
- Limitations to prevent fatigue include:
- Intestines: maximum rate of carbohydrate absorption (1.5-1.7g/min)
- Fluid supplementation is even more important than carbohydrate supplementation during exercise
When, How Much, and in What Form Should Carbohydrates be Consumed Before or During Exercise?
- General recommendations for individuals exercising at 60-80% of their VO2 max for 1-2 hours or longer:
- 4 hours prior to performance: 4-5g/kg of carbohydrates (fiber intake minimized)
- 1 hour prior to performance: 1-2g/kg of carbohydrates (glucose polymers or foods with low glycemic index)
- Within 10 minutes of the start: 50-60g of glucose polymer (40-50% solution)
- During exercise: feedings every 15-20 minutes appear to be a reasonable schedule.
- Sports drinks averaging 6-10% carbohydrates have been found to enhance prolonged endurance performance.
- Type of exercise and carbohydrate needs:
- Maximal exercise lasting less than 45 minutes: none required
- Maximal exercise lasting about 45-60 minutes: <30g/h
- Team sports lasting about 90 minutes: up to 50g/h
- Submaximal exercise lasting more than 2 hours: up to 60g/h
- Near maximal and maximal exercise lasting more than 2 hours: up to 50-70g/h
- Ultra-endurance events: 60-90g/h
Best Practices for Carbohydrate Consumption
- The best effect is observed when carbohydrates are consumed both before and during exercise.
- Type of carbohydrate: no difference between the different types of carbohydrates to enhance endurance performance when used appropriately.
- Glucose polymer solution preparation: 1T (15g) + 200ml water = 7.5% solution.
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Description
Learn about the different types of dietary carbohydrates, their formation, and importance in nutrition. This quiz covers monosaccharides, disaccharides, and polysaccharides.
