Sports Nutrition - HECO 336....

Unit Topics
 

Characteritics of Carbohydrates	Carbohydrate Loading
Digestion and Absorption	Carbohydrate Replacement
Blood Glucose Homeostasis	Carbohydrate Supplement Table
Metabolism  -  Glycolysis	Sugar Substitutes/Alternatives
Storage (Glycogenesis)

Sugar Substitutes/Alternatives
 

Characteristics of Carbohydrates

Carbohydrate should comprise between 50 and 60 percent of all athletes' diets.  For endurance athletes levels up to 70 percent are not unusual.  Th emphasis should be on complex carbohdrates from whole grains, breads, cereal, rice, pasta and vegetables.  Fruits and added sugars should makeup the rest.  Due to their high energy requirements, endurance athletes and adloescents often need to consume calorically dense products to meet their energy needs.

Simple Sugars
The chemical term for sugar is saccharide, single sugars are called monosaccharides and include: glucose, fructose and  galactose.
Glucose - the body's energy source.
Fructose - found primarily in fruits, converted to glucose in the liver.
Galactose - found primarily in milk, converted to glucose in the liver.

When two sugars are combined they become disaccharides and include: maltose, sucrose and lactose.
Maltose - is made from two glucose units and is found in grains.
Sucrose - is made from one glucose and one fructose unit. Small amouts are found in fruits and vegetables but sucrose (know as table sugar) is refined from sugar cane and sugar beets.
Lactose - is made from one glucose and one galactose unit and is the sugar found in milk.
A  Guide to Lactose Intolerance

Complex Carbohydrates - Oligo and Polysaccharides
    Complex carbohydrates are chains (polymers) of sugars linked together.  The most common kinds are amylose (starch), which is a straight chain of glucose in a a1,4 glycosidic linkage. Similar to amylose is amylopectin which is also composed of glucose units, however these chains have branches which slows the amount of time it takes to digest them.  Amylose has an a 1,4 glyosidic linkage with 1,6 branches.
    When carbohydrate chains are hydrolyzed and produce chains with two to ten units they are termed oligosaccharides.  When more than ten units in a chain are produced they are termed polysaccharides.

Grains in Your Diet

 Fiber
 Substances  (usually carbohydrate) which are not digestible by humans are called fiber.  Fiber exists in two forms, soluble (gums, pectins, mucilages, hemicellulose) which disssolve in water forming a viscous solution; and insoluble, (cellulose, lignin, hemicellulose) which simply takes up space in the digestive tract.
 
 

Digestion/Absorption
 
 

Glucose Homeostasis  N = 70-110 

Glucose homeostasis - to maintain blood glucose levels in a normal range (not too high(hyperglycemia) and not too low (hypoglycemia).

Normal Range  -  70 mg/dl - 110 mg/dl
hyperglycemia - high blood glucose; new standard  > 126 mg/dl
hypoglycemia  - low blood glucose:  < 55 mg/dl

Insulin  -  A hormone produced by beta cells (islets of langerhans) of the pancreas in response to rising levels of blood glucose.  Insulin assists glucose to move into cells, thus lowering blood glucose levels.

Glucagon  -   A hormone produced by the alpha cells of the pancreas in response to low blood glucose levels.  Glucagon helps to mobilize glycogen breakdown to glucose in the liver so glucose may enter the blood stream and raise blood glucose levels.

Glycemic Index   p.102 in the text
Glycemic Index is a guideline for the rate at which carbohydrate foods are digested, absorbed and raise blood glucose levels.  Foods are generally catergorized as having a high, medium or low glycemic index.  Carbohydrate foods which contain fiber especially soluble fiber have lower glycemic indexes.  Glycemic index does not take into account consuming foods that also contain protein and fat such as eating a baked potato with butter and sour cream or as part of a meal.

The American Diabetes Association

GLYCOLYSIS 

Glycolysis is the anerobic breakdown of glucose to pyruvate
Glycolysis occurs in the cytoplasm of all tissue with a higher concentration of glycolytic enzymes found in white type IIb fast twitch followed by red type IIa fast twitch and finally the lowest concentration in red type I slow twitch muscle fibers.  The heart muscle is aerobically oriented and does not do well during low oxygen availability.  Glycolysis also utilizes fructose and galactose in small amounts .

Fructose is phosphorylated by fructokinase and ATP to fructose-1-PO4 then aldolase B [liver] splits it into DHAP and glyceraldehyde 3 PO4 where it will proceed through glycolysis.

Glycolysis occurs at all levels of activity and attains an increasing responsibility for work as Vo2 max rises above 50%.  However, the higher the level of aerobic training the athlete has attained, the longer he will be able to use fat as an energy source through aerobic metabolism.
At rest about 40% energy comes from carbohydrate
 AT 70 -80 % VO₂Max  carbohydrate IS THE PRIMARY AND PREFERRED FUEL!

Cori Cycle   - recycling lactic acid
When lactate is produced it migrates out of the muscle cell and is absorbed into the vascular system.  The liver removes lactate from blood and resynthesizes glucose which is then released back into the vascular system where it may be used for glycolysis.  Using lactate to synthesize glucose is one form of gluconeogenesis.

Glycogenolysis - the breakdown of glycogen
Their is an immediate increase in glycogenolysis when muscle begins to contract.  This is facilitated by glycogen phosphorylase [catabolic enzyme] activity which is stimulated by Ca++ at the same time the muscle fiber is stimulated by Ca++.  In the muscle epinephrine is the primary stimulator, in the liver both glucagon and epinephrine are stimulators of glycogenolysis.  Falling blood glucose level stimulate the release of glucagon which acts in the liver.  Glucagon also stimulates gluconeogenesis from amino acids and lactate.
 
 
 
 

AEROBIC METABOLISM [TCA Cycle & ETC]
  Aerobic metabolism may be sustained by a variety of fuels including CHO, amino acids and fatty acids.  The primary sites of entrance include pyruvate for glucogenic amino acids, acetyl CoA for fatty acids and ketogenic amino acids, and at several points in the TCA cycle itself for other amino acids.  The TCA cycle produces H+ or electrons which are processed in the electron transport chain where ADP is regenerated to ATP.  while fat is the primary fuel for this system, CHO must be utilized, thus glycogen stores are essential to maintain endurance activity.
 
 

Glycogenesis -  the formation of glycogen   (Storing Energy for Later Use)
Glycogen formation is stimulated by the presence of insulin which activates the glycogen synthase enzyme.  Insulin is available because high glucose loads have increased the release of insulin.  Insulin moves glucose into muscle cells and the liver.  To concentrate glucose in muscle and the liver, branched chains of glucose are formed [glycogen]  Glycogen occupies less space than individual glucose molecules but has 3-4 grams of water attached to every gram of stored glycogen.  Excess glycogen storage from traditional CHO loading may cause muscle stiffness and actually reduce performance
 
 

Carbohydrate Loading

Carbohydrate
    Supplements
     A variety of products are available  which include simple sugars, complex carbohydrates, and mixtures of both in liquid, gel, powder and bar form.  However, ordinary food items meet the needs of most athletes at a fraction of the cost of commercial products.

FOODS

BEVERAGES	8 oz
BARS
NutriïGrain Bar   (cherry)	37 g	27 g	cherry filling: preserves, HFCS, puree, maltodextrin

COMMERCIAL PRODUCTS

BEVERAGES	Serving	CHO	Kcal	Carbohydrate Sources, etc.	Other  Ingredients
Carbo Pump	2 1/2 scp	8 g	32	glucose polymer
Exceed Carbohydrate replacement	8 oz	59 g		glucose polymers, dextrose, sucrose
Gatorlode
Torq* (fruit juice drink)
GELS
Powergel	41 g	28 g	110	maltodextrin, fructose
Gu	32 g	25 g	100	maltodextrin, fructose	amino acids <1g vit. C & E
BARS
Gatorade Energy Bar	65 g	47 g	250		pro 7g, fat 5g
PowerBar/Performance   (vanilla crisp)	65 g	45 g	230	HFCSa, grape & pear juice conc. oatbran, maltodextrin	pro 9g, fat 2.5g
PowerBar/ Essential (chocolate)	54 g	28 g	180		pro 10g, fat4g; vitamins, minerals,herbs
PowerBar/ Harvest (cherry crunch)	65 g	45 g	240	oats, brown rice syrup, dried fruit, sugar, soy	pro 7g. fat 4g
PYRUVATE					.

* Currently availability limited to the western US (excluding NM,AZ so. CA) plus AK and HI.
  Check availability at:    http://www.gatorade.com/content.cfm?Alias=Torq
^a high fructose corn syrup
 
 

Sugar Substitutes/Alternatives
     For additional Information on limiting sugars in your diet see.......
The Calorie Control Council

  Aspartame
    NutraSweet & Equal
 

  Saccharin
     Sweet & Low

  Acesulfame-K
     Sweet One

  Sucralose
     Splenda
 
 

Home	Carbohydrates	Lipids	Protein
Energy Systems	Muscle Anatomy	Recommendations	Fluids
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 Last Modified: Jul 18, 2000