Carbohydrates for Athletes

Objectives

• Carbohydrates requirements for athletes need to be identified
• Different types of carbohydrates require identification too
• Carbohydrates loading strategies must be understood

Carbohydrates

• The primary source of energy
• The digestive system converts carbohydrates into glucose
• The body uses glucose as energy for cells, tissues, and organs
• They contribute to 60-70% of the body's total caloric needs
• From a nutritional view, are grouped into:
  • Simple carbohydrates
  • Complex carbohydrates

The Role of Carbohydrates

• The body converts carbohydrates into glucose
  • Glucose is the main source of energy
• Unused glucose is stored in the liver and muscles as glycogen
• Glycogen is converted back to glucose when energy is needed
• Excess carbs are converted to body fat rather than glucose

Carbohydrates Stored as Glycogen

• Glycogen is a polysaccharide found in mammalian muscle and liver
• Glycogen is synthesized from glucose during gluconeogenesis
• Glycogenolysis provides a rapid extra muscular glucose supply
• Liver glycogen content is around 80-110g
• Muscle glycogen content is around 400-500g

Functions of Carbohydrates

• The principal source of energy
  • Supplies 60-80% of the body's caloric needs
• Contains 4 kcal per gram
• Spares proteins from being misused for caloric purposes
• The central nervous system is dependent on glucose for energy
• Acetyl CoA is formed in fatty acid oxidation
• Acetyl CoA combines with oxaloacetate, derived from carbohydrate
• Fats need carbohydrate to burn effectively
• Excess fat utilization and carbohydrate deficiency leads to ketosis
• Muscle glycogen breaks down to lactic acid for muscle contraction
• Pentoses are constituents of nucleic acids and coenzymes
  • Pentoses are produced in carbohydrate metabolism
• Intermediates of carbohydrate metabolism serve as non-essential amino acid precursors
• Excess consumption leads to fat formation

Classes of Carbohydrates

• Sugars:
  • Monosaccharides
    • Includes glucose and fructose
  • Disaccharides
    • Includes sucrose, maltose, and lactose
• Polysaccharides:
  • Storage
    • Includes glycogen and starch
    • Animal cells store glucose as glycogen
    • Plant cells store glucose as starch
  • Structural
    • Includes cellulose and chitin
    • Plant cell walls are made of cellulose
    • Chitin is found in arthropod exoskeletons

Monosaccharides

• Glucose (dextrose or blood sugar):
  • Used directly by cells for energy
  • Stored as glycogen in muscles and liver
  • Converted to fat and stored for energy
• Fructose:
  • Called levulose or fruit sugar
  • Absorbed in the small intestine and quickly metabolized in the liver
  • Converts to glucose
  • Forms into fat if consumed in high amounts
  • Often found in fruits
• Galactose:
  • Forms milk sugar called lactose
  • Does not exist in nature in large pure quantities
  • Converted to glucose for energy metabolism

Disaccharides

• Formed when two monosaccharide molecules combine
• Each contains glucose as its main component
• Sucrose (table sugar) includes glucose and fructose
• Lactose (milk sugar) includes glucose and galactose
• Maltose is an ingredient used in alcohol production, includes glucose only

Simple Carbohydrates

• Sugars include fructose and lactose
• Found primarily in fruit and milk
• Sucrose is found naturally in plants
• Refined to make table sugar
• Also added to manufactured foods
• Often referred to as empty calories

Complex Carbohydrates

• Starch and fiber are forms of plant polysaccharides
• Plant starch accounts for 50% of the total carbohydrate intake for Americans
• The term "complex carbohydrate" refers to dietary starch
• Found in:
  • Whole grains
  • Nuts
  • Seeds
  • Legumes and tubers (root veggies)
• Must be broken down into simple carbohydrates to use for energy

Fiber

• Fiber contains vitamins, minerals and fiber
• Indigestible complex carbohydrate in vegetables, fruits and grains
• Helps move waste through the digestive system
• Prevents constipation
• Lowers LDL cholesterol
• Improves blood glucose levels
• Reduces inflammation
• Binds to potential cancer-causing agents

Soluble Fiber

• Slows digestion
• Assists absorption of nutrients from foods
• Dissolves in water
• Forms a gel in the large intestine
• Aids in lowering total cholesterol and improving glycemic index
• Found in oat and rice bran, barley, peas, beans, apple pulp, citrus fruits, strawberries, and psyllium husk

Insoluble Fiber

• Does not dissolve in water
• Increases waste movement
• Decreases cardiovascular risk
• Prevents constipation
• Removes toxic waste
• Found in wheat bran, whole grains, rice, flax seed, nuts, popcorn, cabbage, beets, carrots, brussels sprouts, turnips, cauliflower, and apple skins

Carbohydrate Intake

• Athletes should consume 3-12 grams of carbohydrates per kilogram of body weight
• The amount depends on the training routine
• This percentage is only a guideline for estimating carbohydrate needs

Carb Loading Diet: Marathon, Cycling, Running

• It is the concept of glycogen loading that came from research in Sweden by Drs. Saltin and Hermanson
• Dietary carbohydrates discovered as the major energy source
  • Energy is stored in muscles as glycogen
• Muscle glycogen content links to endurance performance
• Lower concentrations result in premature fatigue
• Nutritional strategies increase muscle and liver glycogen before competition
• Maximizes performance
• Endurance athletes require proper endurance foods for energy and stamina
  • Specifically cyclists, swimmers, and runners performing for >90 minutes

Carb Loading and Pre-Race Fueling

• Carbohydrates are the primary energy source
• A strategy to maximize energy stores for performance
• Normally athletes will load 1-3 days before an event
  • Specifically, endurance athletic events lasting >90 minutes
  • This allows for large storage of carbohydrates
• Studies show the intakes of 8-12g/kg/body mass in the days before
• Reduces fatigue, improves endurance performance

The Purpose of Carb Loading

• To store energy
• Glycogen in the muscles and liver may delay fatigue
• Best in endurance and high-intensity intermittent sports

Carbohydrate Loading and Performance

• Normal muscle glycogen levels:
  • 100-120 mmol/kg
• Carbohydrate loading enables muscle glycogen levels to increase to 150-200 mmol/kg
• Extra carbohydrate improves athletes' endurance exercise by improving the pace
• It is thought to boost performance to 2-3% over a set distance

Who Should Load Carbohydrate?

• Anyone exercising continuously for 90 minutes or longer may benefit
• Typically, sports such as:
  • Cycling
  • Marathon running
  • Longer distance triathlon
  • Cross-country skiing and endurance swimming
• Not practical for team sports where games are played every 3-4 days

Types of Carb Loading

• Increases carbohydrate intake
• Combines foods, drinks, and gels
• Reduced training volume leads to increased glycogen stores
• Can be done from one to six days before an event

Classical 6-Day Regimen

• Three days of intense glycogen-depleting exercise
• Followed by three days of a high-carb diet with no exercise
• Studies suggest depletion in the initial phase will help in producing more glycogen

Modified 6-Day Regimen

• Modified 6-day carb-loading diet includes gradually increasing carbs
  • Decreasing the training volume
• Includes three days of exercise taper and a normal diet
• High carb (70%) and light exercise the three days prior
• Diet must consist of 50% carbohydrate at a minimum
  • Gradually increase
• The minutes of exercise must not exceed 20 minutes by the end

Classic 3-Day Regimen

• Shorter and easier than the six days period
• Perform intensive endurance exercises for the initial phase
• Then, have a high carb diet with no exercise for the rest of the three days

Modified 3-Day Regimen

• Same as the classic three days except that there is no exercise
• Consumes 10 grams of carbohydrate per kilogram of weight a day

1-Day Regimen

• Most simple form of carb loading
• There is no exercise
• A high-carb diet is consumed targeting 10-12g/kg body mass

Risks/ Side effects of Carb Loading

• Slight stomach discomfort (from digestive issues)
  • Avoid high fiber and high-fat foods, and protein
• Stratigically planned diet or excessive calorie intake and overall weight gain

Types of Carbohydrates

• Foods get absorbed by the muscles without gastrointestinal discomfort
• The glycemic index (GI) determines the effect a certain food has on blood glucose
  • High-GI foods are broken down quickly during digestion
  • High-GI foods are absorbed by the muscles effectively
• Glycaemic Load (GL) has a greater quantity of carbohydrates
  • A given weight of food and GI increases carbohydrate absorption
• Large intake of fibrous foods lead to gastrointestinal discomfort
• Focus on lower fibre foods and carbohydrates
• White potatoes are high-GI and GL
  • Removing skins reduces the fibre, making mashed potatoes an ideal choice

Glycemic Index

• Variations increase levels of blood glucose after eating foods containing carbohydrates
• Measured by glycemic index
• Postprandial glucose concentrations from a graph

Calculating Glycemic index of carbohyrate levels

• Glycemic index defined as the area under the blood glucose curve
  • After ingesting the compared food, the blood glucose curve is compared to glucose in the same amount
• The result is expressed as a percentage
• The formula for glycemic index: Area under the blood glucose curve after ingestion of test meal/Area under the curve after ingestion of glucose x100

Glycemic Index Foods

• Foods with high glycemic index foods increases the body’s sugar at a faster rates and and provoke a response in blood sugar levels rapidly
  • Includes; white bread, white rice, potatoes
• Low glycemic index foods increases sugar slowly by releasing glucose gradually into the blood stream
  • Includes; lentils, chickpeas, navy beans
• Glycemic index if lower when combined with protein, fat or fiber

Glycemic Load

• (GL) measures carbohydrate food, and how quickly it affects the level of sugar consumed
• The formula is; GL is calculated: GI of particular food is multiplied by the grams, divide it to 100

Pre-race Meal

• This helps to prioritise to digest carbohydrates with proteins or fluids
• Foods such as honey, or banana
• Lower GI foods; helps in the hours before the race to maintain satiety and enhances the performance

Food to eat

• Foods should be in high carbs, low fat, less fibre is great for carb loading
• Great protein sources, fish and dairy

Food Recommendations

• Include :
  • Low-fiber cereals
  • White bread
  • White rice
  • Sports drinks
  • Low-fat Energy bars
  • Fruit juices and smoothies
  • Fruits (banana, pineapple, and apple)

Foods to avoid

• Higher in carbs and fats
• Should be avoided as they make the stomach uncomfortable
  • Chips
  • Cookies
  • Pizza
  • Ice creams
  • Pastries
  • Cake
  • Donuts
  • Creamy sauce

Foods To Limit

• Include :
  • Beans
  • Lentils
  • Peas
  • Oats
  • Broccoli
  • Raspberries
  • Chickpeas, etc

Carbohydrates and Post-Exercise Recovery

• Replenishing muscle and liver glycogen stores to support subsequent training sessions is crucial
• Consuming carbohydrates and carbohydrates after exercise is important