Chapter 3: Carbohydrates

What are carbohydrates?

• carbon, hydrogen and oxygen

• formed by plants via photosynthesis

• stored in plants as starch

What are simple carbohydrates?

monosaccharides 1 and disaccharides 2

What CHOs are monosaccharides?

glucose, galactose, fructose

What CHOs are disaccharides?

sucrose - glu + fru

lactose - glu +gal

maltose - glu +glu

What are complex CHOs?

oligosaccharides 3-10, polysaccharides >10

Which CHOs are oligosaccharides?

maltodextrin and corn syrup

Which CHOs are polysaccharides?

starch and glycogen

What is dietary fiber?

polysaccharides, nondigestible, plant sources, soluble (stay gelatinous, lower cholesterol) versus insoluble (add bulk to stole, helps digestion)

What are the functions of carbohydrates?

4kcals/g, primary energy source, only energy source for high intensity anaerobic levels, energy source for cells of CNT

metabolic primer for fat metabolism: provides intermediates for energy production from fat breakdown, prevents ketosis

prevents protein catabolism in body: decreases gluconeogenesis, spares muscle tissue

What are phytochemicals?

found in plants, antioxidants, enhance immune function

What is fiber related to?

• reduced risk of heart disease (cholesterol lowering)

• reduced risk of cancer (phytochemicals, antioxidants, decreased intestinal transit time)

• improved weight management (feeling of fullness)

Why are simple sugars (refined sugars) harmful for health?

dental cavities, weight gain

What are the recommendations for CHO intake?

• 3-12g/kg of bw

• 50-65% of total daily calories

  • as high as 75% during carb loading

• recommendations will change based on athletes stage of training and competition schedule

What are sources of carbohydrates?

• whole grains

• veggies and fruit

• dairy/dairy alternative products

• beans, lentils, nuts, seeds and soy products

• sweets

What is the glycemic index?

• body’s increase in BG and insulin after consumption of given food, glycemic effect of isolated food

• based on blood sugar levels 2 hrs after ingestion

• based around piece of white bread (GI = 100)

What is glycemic load?

glycemic effect on diet

What are limitations of GI and GL?

not everyone responds the same, other macronutrients = different effect

How useful are GI and GL in sports nutrition?

• timing eating around practice/game

• high GI foods before competition for energy

• foods low in GI tend to be higher in fiber

What is hypoglycemia?

eating bunch of carbs too close to exercise = feeling shaky

What is rebound hypoglycemia?

drop in BG due to additive effect of intensity and exercise

What is the importance of CHO in exercise?

• main energy source

• becomes side source of energy during very intense exercise

• limited store

• carbs increase the time to exhuastion

What factors determine CHO needs during exercise?

frequency, duration, intensity (primary factor), type, environmental conditions, nutrition status (fasted, just ate, fullness of glycogen stores)

Where do CHO come from during exercise?

• endogenous (liver - gluconeogenesis)

• BG

• muscle and liver glycogen stores

• exogenous sources

What determines if gluconeogenesis is used during exercise?

• CHO levels before

• CHO ingested during exercise

• mode, intensity, duration

• environment - anything limiting O2 delivey = increase CHO use

• aerobic fitness (endurance)

Why don’t we want to rely on gluconeogenesis during exercise?

because it’s slower and relies on proteins, increases fatigue and lowers performance

Why is 3 days depletion followed by 3 days of loading not beneficial?

• reduces practice performance

• makes athlete feel bloated during competition

What should an athlete eat 4-24 hours before competition?

• balanced high-CHO meals/snacks

• familiar foods

• CHO = 60-70% total calories

What should an athlete eat 0-4 hours before competition?

• 1-4g/kg

• easily digested, low fiber

• complex carbs

• carb-rich protein sources

• fluids - 2c 2hr prior, 1c 1 hr prior, 7oz 30 min prior

What should an athlete eat during competition?

• 30-60g/hr

• up to 90g/hr ultra endurance events

• begin soon after onset, continue at regular intervals

• liquid form is best for 1) rate of gastric emptying 2) intestinal absorption

What types of carbs are recommended to ingest during competition?

variety

What should an athlete eat after competition?

• consumed asap

• 4:1 carb to protein ratio

• 1-1.2g/kg every 4 hours

• factors

  • 1) timing CHO

  • 2) type of CHO and inclusion of other macros

  • 3) quality of CHO in post exercise snack

Why is it important to experiment during practice and not during/before a game?

how the body will react is unknown and could decrease performance

What’s the difference between complex and simple carbs?

• complex - primarily starches

  • chemical structure

  • good source vitamins, minerals and fibers

• simple - processed foods

  • glucose, sucrose, fructose, high-fructose corn syrup

  • low in vitamins, minerals, fiber

Is it true that simple CHOs have a higher GI than complex?

no, it isn’t that simple

Why is it important to know the factors of CHO used during exercise?

to help prolong fatigue and increase performanceWh

What source of CHO do we want to spare and why?

liver glucose because it’s last resort and the maintainace of BG is needed

Gluconeogenesis is the opposite of which metabolic pathway?

glycolysis

What are the substrates of glucoenogenesis?

• lactate - CHO

• pyruvate - CHO

• alanine - PRO

• glycerol - FAT,

What happens to glucose when it goes into the muscle?

once it goes to muscle it cannot share, give off lactate and converted to glucose (gluconeogenesis)

What is the cori cycle?

• Lactate

  • working muscles get depleted, non-working muscles share lactate

  • conversion lactate to glucose in live

What is the relationship between aerobic lactate threshold and MG depletion?

stores deplete = decrease lactate threshold bc body is breaking glucose causing an increase in H+

What are the hormonal controls of CHO metabolism in exercise?

• epinephrine/norepinephrine - stimulate fat and CHO breakdown

• insulin - decreases or remains the same

• glucagon - increases

  • released from pancreases to increase BG (stimulator of glycogenolysis and gluconeogenesis)

What are the effects of various horomones on fuel production?

• cortisol - simulates gluconeogenesis, helps mobilize FFAs and AAs

• epinephrine - promotes gluconeogenesis in muscle+live, activates lipolysis in adipose tissue, raises BG and FA levels

• glucagon - released BG low, stimulate gluconeogenesis + glycogenolysis

• insulin - maintains BG, increase synthesis glycogen from glucose, decrease gluconeogenesis, promotes lipogenesis (inhibits fat mobilization)

Where is glycogen concentration the highest?

in the liver

What are the goals of CHO fueling before exercise?

• promote additional glycogen synthesis

• supply body with glucose

• minimize fatigue during exercise

• avoid discomfort

When should CHO be consumbed during exercise?

• mod intensity 60-80% >60 minutes

• long duration >90 minutes

What does research show about CHO feeding during exercise?

improved performance with or TTE (time to exhaustion)

What is the progression of sources of energy as exercise duration increase?

1 - muscle glycogen and muscle triglycerides

2 - increase blood glucose and FFA

What is hypoglycemia?

glucose output from liver can’t keep up with demands of working muscles

What type of CHO should be consumed?

all simple sugars, combo is best option - increases ability of various transport mechanisms

What simple sugar should be “avoided” and why?

fructose - can’t maintain BG, large amounts cause GI distress, slower oxidation rate, muscles not take up fast = lower insulin response

works well in combo w/ other sugars post exercise

What is rapid and slow glycogen synthesis?

• rapid

  • 30-60 min post exercise

  • not require insulin

  • occurs if MG is low

• slow

  • several hours

  • insulin dependent

  • CHO and insulin levels high

  • 90% ingested stored in MG (priority over LG)

  • greater depletion enhances synthesis

What is the relationship between CHO and protein?

CHO + Pro = 17-26% more glycogen synthesis

Why is the role of protein in exercise?

• resistance training

  • tissue growth

  • tissue repair

• aerobic training

  • energy expenditure

  • tissue repair

What does the amount of glycogen stored after exercise depend on?

• total energy intake

• CHO content of diet