Carb Loading, Glycemic Index and Glycemic Load

Nelson PE pages 93 and 94, 345 and 347

Food Fuel used during exercise and rest.

• Carbohydrates – preferred fuel source during exercise. Contribute about 1/3 of energy at rest.

• Fats – preferred fuel source at rest (contribute 2/3 of energy) . Also used during sub-maximal exercise in addition to carbs.

• Protein – usually used for growth and repair but is used as a last resort if the body is starved of other sources.

Glycemic index

• Glycemic index (GI)- measure how quickly a food releases sugar into the bloodstream.

• Low glycemic index foods are better to eat before physical exercise because the energy last longer.

• Glycemic load – GI x carbohydrates in grams per serving.

Basal metabolic rate

• The amount of energy used at rest.

Factors that affect GI

• Fatty foods can delay stomach emptying and slow release of sugar into the blood.

• Organic acids can lower GI e.g. vinegar• Physical entrapment of sugars within food.• Type of starch involved.

GI and endurance sports

• Low GI foods should be consumed 45 to 60 minutes before exercise.

• High GI food reduce performance if consumed in this period.

• High GI foods need be consumed immediately before exercise.

Carbohydrate loading

• In sports such as marathons where you exert yourself for long periods without a chance to refuel it carb loading is a strategy used to make sure there is stored carbs available for the body to use.

• Not useful for teams sports where you have a chance to eat and only exert yourself in bursts.

Practical exercise

• Look at cereal boxes and work out the GI and GL.