ch 13 Flashcards
Why is nutritional advice varied and contradictory?
-food is complex
-interaction between food and physiology is complex
-exercise affects the food-physiology interaction
-the way food is grown
-nutritional info is contradictory
-dose-response relationships
-advice is contrary to evolutionary logic (eggs and cholesterol misconception)
-ancestry and genetic adaptations
-incorrect research
-too many rules for the public to digest
-nutritional guidelines can be influenced by companies
how to evaluate claims suggesting a single optimal diet?
-we don’t really know what our ancestors ate
-might seem “logical” but not based on true science
-rule of thumb= stay away from processed foods
traditional diets low in processed foods
traditional diets are all low in processed foods, once they adapted to western diets –> much more diseases and health problems
glycemic index
amount of blood glucose after eating carbohydrates
why do nutritionists prefer “glycemic load” over glycemic index?
glycemic index does not take into account the AMOUNT of food consumes (same for 1 rice cake vs 10 rice cakes)
glycemic load= multiply grams of carbohydrates by the glycemic index and divide by 100
Major fuel for exercise
carbohydrates (4kcal/g) and fats (9kcal/g) are the major fuel during exercise
Under normal circumstances, our muscles have 4 major energy sources
- Plasma (blood) glucose-
- Muscle glycogen
- Intramuscular triglycerides
- Plasma fatty acids
Blood glucose:
-which hormones regulate it?
insulin and glucagon
-they are produced in the pancreas
Blood glucose: how does it work?
-after meal
-glycogen stores full
-blood glucose decreases
after a meal, blood glucose it higher, liver removes excess glucose from blood and stores it as glycogen.
if glycogen stores are full, excess blood sugar will be stored as fat in adipose tissue.
If blood glucose decreases, the liver releases stored glycogen to be broken down to glucose
–> even blood lactate can be converted to glucose during exercise!!
Muscle glycogen: what does it depend on?
-higher exercise intensity= higher use of glycogen
-muscles involved in the exercise: glycogen will be depleted in muscles that are used
-type of muscle fibre or motor unit recruited (type 2 prefers glycogen/glucose: bc higher intensity/speed, more power w type 2 fibres)
Explain how exercise intensity is related to muscle glycogen
higher exercise intensity= higher use of glycogen
ex. walking slowly, will not use much muscle glycogen
but walking quickly= near VO2 max= using more glycogen
Explain Gluconeogenesis
when glycogen levels are too low, the body makes glucose from protein
–> this occurs during low carbohydrate diets (less than 30% total kcal)
“gluco”= glucose
“neo”= new
“genesis”= creating
Would there be more glycogen usage during uphill or level running?
the muscles that are recruited for running experience greater glycogen usage running uphill
–> maximizing glycogen stores in quadriceps can help w running uphill
–> but running on uneven terrain can quickly deplete glycogen in muscles if not trained for it
Explain the relationship between muscle glycogen and slow/fast twitch fibres in the “distance run”
–> vastus lateralis
distance run= recruiting more slow twitch fibres (so they will be depleted much faster than fast twitch)
Sprint bouts on a stationary bike: which muscle fibres will be depleted faster? (in the vastus lateralis)
fast twitch fibres will be depleted faster
how is blood glucose protein sparing?
if we don’t have enough glycogen, gluconeogenesis occurs (amino acids –> glucose)
fat can’t be converted into carbohydrates
consuming enough carbohydrates is recommended to prevent gluconeogenesis
Fat (intramuscular triglycerides and plasma fatty acids)
–> when are fat stores used for energy
other main source of fuel during exercise
there will always be enough fat fuel, even in ulta-long endurance events
–> pushing bodily limits= depletion of intramuscular triglycerides
Intramuscular stores account for – of the fat used in endurance events
half
If enough calories from fat and carbs are available, the breakdown of amino acids only accounts for –% of total energy used
2-5%
–> but during end of exercise lasting 3-5 hours, protein use may reach 5-15% of total fuel supply
Factors that govern the selection of fuels during muscular work (2)
Intensity of endurance exercise
Duration of endurance exercise
Explain intensity of endurance exercise in selection of fuel (at rest, at 95% VO2 max)
At rest: 2/3 ATP production comes from fatty acids, 1/3 from glycogen and glucose
At 95% of VO2 max and above: carbohydrate is used almost exclusively
Explain duration of exercise in selection of fuels
Intensities between 65-85% of VO2 max, it takes 80-120 min to deplete glycogen stores
As endurance increases, the proportion of energy produced from fat increases
Carbohydrate and Fat metabolism during prolonged (duration) exercise
–> which fuel is depleted first?
–> and what information is missing from the graph?
as duration increases, fat is mostly metabolized for fuel
less fuel from carbs
glycogen depletion during 30km run (2.5 hr), 86km xcountry ski (7 hr), and 100km run (12 hr)
–> why does 7hr xcountry have greater glycogen depletion than 12hr 100km run?
xcountry ski= more intense, more muscle groups used
fitter people are able to use – for fuel longer than a less fit person for the same workload
fats
why is it better to use fats as fuel for longer?
because of the theoretical “endless” fuel of fats stored in our body
–> very high intensity= carbohydrates as fuel
A person on a high carb diet will have higher — levels
muscle glycogen
training with low carbohydrate availability can improve…
the body’s ability to metabolize fats
(strategically training w low carbs on some days)
–> beneficial for endurance races
Carbohydrate and work time
–> explain graph/study
time to exhaustion was much higher with a high carb diet
–> idea of carb loading came from this study
Glycemic index and exercise: when to consume?
diet w a lot of high GI foods are usually bad
–> high GI foods prior to exercise may be a problem
but glucose feeding DURING exercise is essential for endurance training
–> high GI foods can HELP refuel carb stores after exhaustive exercise (most people don’t exercise hard enough to need this)
Explain rebound hypoglycemia
dramatic drop in blood glucose levels after consuming high GI carbs before exercise
–> blood glucose spikes, insulin released to pick up as much glucose as possible, but ALL cells pick it up (not just muscle cells), not ideal for exercise bc blood glucose drops
Explain consuming a glucose polymer during an endurance competition
blood glucose goes down during exercise, coming glucose during exercise helps to maintain enough glucose in blood
Explain difference in energy consumption breakdown between strength/power athletes vs. endurance athletes
endurance= more kcal, more carbs
strength/power= more protein
fats stay the same
challenges in counting calories
not accurate, especially if using a watch to track calories
–> focus on performance and a well-balanced diet
