Transcript Optimal Nutrition for Exercise

Optimal Nutrition for Exercise
Stored energy
Energy is stored as body fat or glycogen (carbohydrate in
muscles and liver) & is broken down to provide energy.
Glycogen is the main source of energy during short
bursts of activity & at the start of exercise.
Only a small store of glycogen in the body  as exercise
continues the store becomes depleted =the body starts
to use fat to provide energy.
Fitter athletes use up store of glycogen more slowly &
tend to use stores of body fat for fuel more easily.
The importance of carbohydrates
High carbohydrate diet = muscle & liver glycogen stores
are maintained.
If most of the glycogen in muscles and liver is used (after
prolonged exercise) blood sugar levels can drop below
normal = fatigue, nausea, dizziness.
Carbohydrate rich foods are also
important for replenishing glycogen
stores after an event.
Protein needs
Athletes need slightly more protein to repair & build
muscle.
Athletes generally eat more (to meet energy
requirements) = meet protein needs by choosing a
balanced diet.
They do not need to consume food high in protein.
Athletes do not need large amounts of meat or to
take supplements.
Eating more protein than the body needs does not
increase the amount of muscle in the body.
• Protein
- 0.83g per kg  adequate for physically active
- 1.2g per kg  intensive training
• Lipids
-Standards not firmly established
- Asia 10%; Western 40-45%
- Should not exceed 30% of diet
 70% should be in the form of unsaturated FA
High Protein Diet?
 Extreme high protein diets:
- displace other nutrients from diet
- expensive (often higher in saturated fat)
- increase dehydration
- promote calcium loss from bones
 Excess protein is not stored – it is used as an
energy source or is converted to fat
High Fat Vs. Low fat diets for Exercise
Training
High Fat diets:
- Shift in substrate use to wards higher fat use
during exercise
But: high carb = better for endurance performance
 increased fatigue & higher perceived exertion
Low fat diets:
Restricting dietary fat below recommended levels =
impairs performance
Contemporary approach: High fat diet
• High fat diet will slow down
rate of muscle glycogen use
Benefits:
1. Muscle glycogen will be maximised (because not
using them)
2. Muscle glycogen used at slower rate (because
not using them)
3. Can still exercise when muscle glycogen is low –
fat drives performance
Carbohydrate diet:
- Low carb diet compromises glycogen reserves
- Physically active – 55-60% calories from carbs
- Competitive athletes:
high daily carb intake relates
more to high energy demands
of training rather than the
short term demands of the
competition
Intensive training:
- Regular intensive training = increase carbs to
allow glycogen resynthesis
Pre-competition meal
• Fasting = rapidly depletes liver & muscle
glycogen  impairs performance
•
-
NB:
Food preference of athlete
Psychological set of competition
Digestibility of food
PREPARATION
• Pre-event food: high carb, low fat
– Larger meal 3 – 4 hrs before:
• Cereal, skim milk & fruit / Toast with
baked beans
– Smaller snack 1 – 2 hrs before:
• Banana / Bread with honey
Carbs prior to exercise
• No carbs 1 hour before = rapid rise in blood
sugar  hyperglycemia = impairs CNS
• High insulin levels inhibit lipolysis = premature
glycogen depletion & early fatigue
Carbs during exercise
• Eat carbs during exercise = improves performance
 delays fatigue (15-30mins)
• Ingested carbs provide readily available energy
for active muscles
• ±60g carbs each hour benefits high intensity, long
duration exercise
spare muscle glycogen (esp. type 1 slow twitch)
maintains optimal blood glucose level
 Lowers RPE
• Single, concentrated feeding ± 30mins before
perceived exhaustion/ fatigue  restore
blood glucose
• Fats = primary energy source in light –
moderate exercise
How much Carbs?
During Training/ event:
 30 – 60g per hour
 In each 600mL powerade drink = 46g
 2.5 muesli bars = 50g
 2 bananas = 50g
Nutritional Periodization
• Train for most of year on high carb diet
• High fat diet 7 -10 days in 2 weeks before
competition/ event
• High carb diet in last 3 days before
competition
Periodization of Calorie Needs
• Competition day:
Exclude foods high in fats & proteins
slow to digest
Stays in intestinal tract longer
makes athlete feel bulky & heavy
Timing: 3-4hours to digest & store carb-rich food
* Meal should maximize liver & muscle glycogen +
provide glucose for intestinal absorption during
exercise
Carbohydrates after event
After exercise:
Athletes should consume 1.0 to 1.5 g of carbs per
kg body weight immediately post exercise & again
one hour later
To replace muscle glycogen stores
To prevent gradual depletion of muscle glycogen
stores over time caused by repetitive daily bouts
of heavy exercise
To decrease muscle breakdown
Ideal Meal?
• 150-300g of carbs
• 3-4hours before event
• Low in fat & fibre
*Liquid meals:
High in carbs  digest rapidly, supplies fluid & practical
** Don’t substitute meals with protein/ energy bars 
lack plant fibres & contain high levels of saturated fats
*** Don’t substitute meals with nutrition powders/ drinks
 contain high protein levels & lack plant fibres
Too little energy?
If an athlete’s diet contains too little energy from
carbohydrates, protein from the diet will be used to
provide energy.
Not desirable  less protein will be available for
forming and repairing muscle tissue
Carbohydrate should be the main source of energy.
Some fat can also contribute to the body’s energy
source.
Hypoglycemia & Fatigue
• Low blood sugar (glucose)
• First reported in Marathon runners (1924)
• 1925: Eat high carb diet day before & ate
sweets after 24km
 No depletion of blood glucose = performance
improved
• Noakes 1980: Comrades
- Wasn’t prepared
- After 60km = difficulty in concentrating
- Mind would clear 5min after drinking 100ml
coke
- 65km pace began to fall
- 80km Had to sit down
- Other runners
had similar responses
Signs of hypoglycemia
• Feeling weak, fait, giddy
• Intense craving for sweets
• Pace has huge effect on hypoglycemia
• Marathon at 85%VO2max:
Muscle glycogen can supply energy for 115mins
Liver glycogen can supply energy for 140mins
• Ultra-marathon: 70-75%VO2max
Muscle glycogen: 310mins
Liver glycogen: 140-220mins
*Muscle glycogen outlasts liver
glycogen = Need to replenish
carb stores
** Ultra-marathon runners limited by onset of
hypoglycemia (compared to standard marathon
runners).