Optimal Nutrition for Exercise

Stored energy Energy is stored as body fat or glycogen (carbohydrate in muscles and liver) & is broken down to provide energy. Glycogen is the main source of energy during short bursts of activity & at the start of exercise. Only a small store of glycogen in the body  as exercise continues the store becomes depleted =the body starts to use fat to provide energy. Fitter athletes use up store of glycogen more slowly & tend to use stores of body fat for fuel more easily.

The importance of carbohydrates High carbohydrate diet = muscle & liver glycogen stores are maintained. If most of the glycogen in muscles and liver is used (after prolonged exercise) blood sugar levels can drop below normal = fatigue, nausea, dizziness. Carbohydrate rich foods are also important for replenishing glycogen stores after an event.

Protein needs Athletes need slightly more protein to repair & build muscle. Athletes generally eat more (to meet energy requirements) = meet protein needs by choosing a balanced diet. They do not need to consume food high in protein. Athletes do not need large amounts of meat or to take supplements. Eating more protein than the body needs does not increase the amount of muscle in the body.

Protein g per kg  adequate for physically active - 1.2g per kg  intensive training Lipids -Standards not firmly established - Asia 10%; Western 40-45% - Should not exceed 30% of diet  70% should be in the form of unsaturated FA

High Protein Diet?  Extreme high protein diets: - displace other nutrients from diet - expensive (often higher in saturated fat) - increase dehydration - promote calcium loss from bones  Excess protein is not stored – it is used as an energy source or is converted to fat

High Fat Vs. Low fat diets for Exercise Training High Fat diets: -Shift in substrate use to wards higher fat use during exercise But: high carb = better for endurance performance  increased fatigue & higher perceived exertion Low fat diets: Restricting dietary fat below recommended levels = impairs performance

Contemporary approach: High fat diet High fat diet will slow down rate of muscle glycogen use Benefits: 1.Muscle glycogen will be maximised (because not using them) 2.Muscle glycogen used at slower rate (because not using them) 3.Can still exercise when muscle glycogen is low – fat drives performance

Carbohydrate diet: -Low carb diet compromises glycogen reserves - Physically active – 55-60% calories from carbs - Competitive athletes: high daily carb intake relates more to high energy demands of training rather than the short term demands of the competition

Intensive training: - Regular intensive training = increase carbs to allow glycogen resynthesis

Pre-competition meal Fasting = rapidly depletes liver & muscle glycogen  impairs performance NB: -Food preference of athlete -Psychological set of competition -Digestibility of food

PREPARATION Pre-event food: high carb, low fat – Larger meal 3 – 4 hrs before: Cereal, skim milk & fruit / Toast with baked beans – Smaller snack 1 – 2 hrs before: Banana / Bread with honey

Carbs prior to exercise No carbs 1 hour before = rapid rise in blood sugar  hyperglycemia = impairs CNS High insulin levels inhibit lipolysis = premature glycogen depletion & early fatigue

Carbs during exercise Eat carbs during exercise = improves performance  delays fatigue (15-30mins) Ingested carbs provide readily available energy for active muscles ±60g carbs each hour benefits high intensity, long duration exercise  spare muscle glycogen (esp. type 1 slow twitch)  maintains optimal blood glucose level  Lowers RPE

Single, concentrated feeding ± 30mins before perceived exhaustion/ fatigue  restore blood glucose Fats = primary energy source in light – moderate exercise

How much Carbs? During Training/ event:  30 – 60g per hour  In each 600mL powerade drink = 46g  2.5 muesli bars = 50g  2 bananas = 50g

Nutritional Periodization Train for most of year on high carb diet High fat diet days in 2 weeks before competition/ event High carb diet in last 3 days before competition

Periodization of Calorie Needs

Competition day: Exclude foods high in fats & proteins  slow to digest  Stays in intestinal tract longer  makes athlete feel bulky & heavy Timing: 3-4hours to digest & store carb-rich food * Meal should maximize liver & muscle glycogen + provide glucose for intestinal absorption during exercise

Carbohydrates after event After exercise: Athletes should consume 1.0 to 1.5 g of carbs per kg body weight immediately post exercise & again one hour later  To replace muscle glycogen stores  To prevent gradual depletion of muscle glycogen stores over time caused by repetitive daily bouts of heavy exercise  To decrease muscle breakdown

Ideal Meal? g of carbs 3-4hours before event Low in fat & fibre *Liquid meals: High in carbs  digest rapidly, supplies fluid & practical ** Don’t substitute meals with protein/ energy bars  lack plant fibres & contain high levels of saturated fats *** Don’t substitute meals with nutrition powders/ drinks  contain high protein levels & lack plant fibres

Too little energy? If an athlete’s diet contains too little energy from carbohydrates, protein from the diet will be used to provide energy. Not desirable  less protein will be available for forming and repairing muscle tissue Carbohydrate should be the main source of energy. Some fat can also contribute to the body’s energy source.

Hypoglycemia & Fatigue Low blood sugar (glucose) First reported in Marathon runners (1924) 1925: Eat high carb diet day before & ate sweets after 24km  No depletion of blood glucose = performance improved

Noakes 1980: Comrades - Wasn’t prepared -After 60km = difficulty in concentrating -Mind would clear 5min after drinking 100ml coke -65km pace began to fall -80km Had to sit down -Other runners had similar responses

Signs of hypoglycemia Feeling weak, fait, giddy Intense craving for sweets Pace has huge effect on hypoglycemia Marathon at 85%VO2max: Muscle glycogen can supply energy for 115mins Liver glycogen can supply energy for 140mins

Ultra-marathon: 70-75%VO2max Muscle glycogen: 310mins Liver glycogen: mins *Muscle glycogen outlasts liver glycogen = Need to replenish carb stores ** Ultra-marathon runners limited by onset of hypoglycemia (compared to standard marathon runners).