Utilization
- Fuel for activity
- Immediate fuel for activity
- Sustained energy for aerobic activity
- Major energy for high intense activity like weight training
or sprinting
- Protein sparer - nervous system uses carbohydrates
- Lack of carbohydrates causes protein to go through gluconeogenesis
(conversion of protein to glucose) and be metabolized
- Contrary to popular belief, brain can metabolize lactate
and ketones as well
- Lactate (and other nutrients) also shuttle from astrocytes
to neurons (Rev Med Suisse Romande, 2000)
- Carbohydrates are metabolic primers, they are needed to completely
burn fat
- Incomplete combustion of fat will result in ketone bodies
- Fat burns in the flame of carbohydrates.
- Carbohydrates are the primary fuel for the CNS.
- Accute carbohydrate depletion may cause tunnel vision, nausea,
irritability
- Metabolism can adapt to prolonged low carb, high fat/protien
diet.
Requirements
- Too little carbohydrates
- More fat utilized as fuel source
- Endurance can be reduced up to 50% until metabolism adapts
- Glycogen stores become depleted
(Costill and Miller, 1980)
- Ketosis: Break down of protein (muscle wasting) and incomplete
combustion of fats (ketone bodies)
- Possible symptoms: weakness, dizziness, tunnel vision, fatigue,
panting, abnormal EEG, strange breath
- Possible symptoms in diabetics: unconsciousness, coma and
even possibly death in rare cases
- Blood acidosis may impair exercise tolarance and performance.
- Body can adapt and convert dietary protein to carbohydrates
via gluconeogenesis
- If low carbohydrate diet is coupled with insufficent dietary
protein or calories
- risk of burning lean tissue (muscle) by gluconeogenesis
- Too many carbohydrates
- Converted to fat and stored
- Increases body fat by suppressing fat oxidation
Recomendations for athletes or
physically active
- 50%-60% of calories should be carbohydrates
- 40%-50% from complex carbohydrates
- 10% from simple sugar
- Carbohydrate feedings during long duration (> 90 min.)
submaximal (<70% VO2) can improve endurance performance (Coyle
E & Montain S, 1992; Maughan R, 1991).
- Carbohydrate ingestions of 30 to 60 grams per hour are required
to improve performance
-
Glycemic Index (GI)
- High glycemic indexed food should be eaten with other foods
- Soluble fiber, fat, acidic foods, and protein (particularly
meat) significantly blunts insulin spike
- Keep blood sugar stable
- Inhibit hunger shortly after meal or snack
- All values based on 50 grams of Carbohydrates
- Does not take into account variations of portion size
- Example: how often does someone eat 50 grams of carbohydrate
of carrots?
Glycemic Load (GL)
- Takes into account fiber content and portion size of food
- GL = GI x Carb (grams) / 100
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