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.
- Acute carbohydrate depletion may cause tunnel vision, nausea,
irritability
- Metabolism can adapt to prolonged low carb, high fat/protein
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 tolerance and performance.
- Body can adapt and convert dietary protein to carbohydrates
via gluconeogenesis
- If low carbohydrate diet is coupled with insufficient dietary
protein or calories
- risk of burning lean tissue (muscle) by gluconeogenesis
- Too many carbohydrates
- Increases triglyceridef5r levels
- Converted to fat and stored
- Increases body fat by suppressing fat oxidation
Recommendations 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
- Keeps blood sugar stable
- Inhibit hunger shortly after meal or snack
- GI monitoring may not have applicability in real world
- Food is typically eaten with other foods
- Breakfast is only time we eat after fast
- Studies show those who eat lower GI diet
- do not have significantly lower blood glucose levels
- do not lose more weight
- 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
GI (Glycemic Index) is a percentage expressed as decimal relative
to white bread
|
Food |
Serving Size |
Carbs (g) |
GI |
GL |
|
Potato, baked |
1 medium |
37 |
1.21 |
45 |
|
Grape-Nuts (cereal) |
1/2 cup |
47 |
0.95 |
45 |
|
Cornflakes (cereal) |
1 cup |
26 |
1.19 |
31 |
|
White rice, cooked |
1/2 cup |
35 |
0.81 |
28 |
|
Pasta, cooked |
1 cup |
40 |
0.71 |
28 |
|
Cheerios (cereal) |
1 cup |
22 |
1.06 |
23 |
|
White bread |
2 slices |
24 |
1.00 |
22 |
|
Beans, cooked |
1/2 cup |
27 |
0.60 |
16 |
|
Corn Chips |
1 oz |
15 |
1.05 |
16 |
|
Whole-grain bread |
2 slices |
24 |
0.64 |
15 |
|
Wild rice, cooked |
1/2 cup |
18 |
0.78 |
14 |
|
All-Bran |
1 cup |
24 |
0.60 |
14 |
|
Carrots, cooked |
1/2 cup |
8 |
1.31 |
10 |
|
Lentils, cooked |
1/2 cup |
20 |
0.41 |
8 |
|
Popcorn, air-popped |
1 cup |
5 |
0.79 |
4 |
Ornish, D (2007), The Spectrum, Ballantine Books, New York.
|
|