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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) Ketogenesis Triggered when glycogen store are depleted Fasting, low carbohydrate diets, prolonged exercises Liver produces ketone bodies acetoacetat and ß-hydroxybutyrate via incomplete combustion of fats Ketone bodies are used for energy State of Ketosis Possible symptoms: weakness, dizziness, tunnel vision, fatigue, panting, abnormal EEG, strange breath (acetone) Possible symptoms in diabetics: unconsciousness, coma and even possibly death in rare cases Blood acidosis acid-base homeostasis in the blood is normally maintained (>7.35) through various buffering systems may impair exercise tolerance and performance. Blood glucose levels are initially maintained by converting dietary protein to carbohydrates via gluconeogenesis After about 48 hours, brain utilizes ketones, decreasing reliance on gluconeogenesis thereby decreasing depletion of protein from muscle. If low carbohydrate diet is coupled with insufficient dietary protein or calories protein from lean tissue (muscle) continues to be metabolized by gluconeogenesis Too many carbohydrates Increases triglyceride levels Converted to fat and stored Increases body fat by suppressing fat oxidation Types of Carbohydrates Simple Monosaccharides Fructose, Glucose, Galactose Disaccharides Lactose, Sucrose, Maltose Intermediate Oligosaccharides Repeating units of monosaccharides with glycosidic bonds Eg: raffinose and stachyose found in legumes Metabolized in large intensine with with assistance of bacteria Gas producing Complex Polysaccharides Typically monomer consisting of thousands of repeating glucose Straight chain Amylose Branched Amylopectin Glycogen Fiber Dietary Fiber Undigestible and resistant starches Eg: cellulose, hemicellulose, pectin, gum and mucilage May help in prevention or treatment of certain diseases heart disease, cancer, obesity, diabetes, and hypertension Types Soluble fiber: reduction of serum cholesterol Insoluble fiber: decreases constipation and reduction of colon cancer Resistance starches 20-35 grams recommended Pinto bean and apple supply soluble fiber requirements 40-50 may cause gas; may need to increase fluid intake Fructose Simple sugar found in many plants Eg: fruits, table sugar, high fructose corn syrup (HFCS) Absorbtion and metabolism Lower Glycemic Index as compared to glucose Absorbed from the gastrointestinal tract by a different mechanism that is glucose Metabolized primarily in the liver Also see Fiber's effect on Insulin Refined fructose Chronic consumption of refined fructose linked to metabolic syndrome Diets high in refined fructose increase appitite which may contribute to excessive caloric consumption (Teff, et al. 2004). Recommendations Athletes or Physically Active 50%-60% of calories from carbohydrates have traditionally been recommended 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 Also see High Fat Diets Effect on Endurance. Weight Managment See Macronutrient Ratio Studies. Glycemic Index (GI) GI is a measure of the effects of carbohydrates on blood sugar levels 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) 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.