CONVERSION OF FOOD TO ENERGY

Week 12

What you need to know…

What happens when CHO break down? How are CHO used? What is the glycemic index? High GI & Low GI

examples How can GI be used to benefit performance? How are fats used? How is protein used? What is the importance of fluid?

Introduction When food is digested, _____________ is

released The amount of energy released from food is

measured in kilojoules The three main food fuels are:

• Fat• 38 kilojoules per gram

• Carbohydrate• 17 kilojoules per gram

• Protein• 17 kilojoules per gram

Carbohydrates (CHO)

Most readily available source of energy to fuel working muscles

Digestion breaks CHO down to simpler forms to use for energy

• _____________ (stored in the blood)

• _____________ (stored in the muscles and liver)

• Any excess CHO is stored as fat

• Triglycerides (muscles)

• Adipose tissue (around the body)

Carbohydrates (CHO) The body uses glycogen as one of its major

fuels during exercise CHO are versatile. Predominant supplier of

energy for:• High intensity, short duration activities (lactic acid

system)• Eg:

• Repeated work periods (restoring ATP-PC system)• Eg:

• Sub-maximal, longer duration activities (aerobic system)• Eg:

CHO Needs of the AthleteSituation Recommended CHO

Everyday activity <90mins

Low intensity

5-7 grams per kg of body mass

Training programs >90-120mins 7-10 grams per kg of body mass

Pre-event meal Meal eaten 1-4hrs pre-competition

1-4 grams per kg of body mass

CHO intake during training sessions & competition events >1hr

60 grams per hr

Rapid recover after training session or multi-day competition

1 gram per kg of body mass in first 30mins, repeated every 1-2hrs until normal meals resumed

Glycemic Index A ranking of _____________ according to how quickly

they are digested and therefore release energy, as well as the way they affect blood glucose levels

Foods that break down _____________ have the highest glycemic index

• Blood glucose response is fast and high

• Appropriate for recovery of muscle glycogen stores after strenuous exercise

Foods that break down _____________ have low glycemic indexes

• Slower rise in blood glucose

• Appropriate for pre-event meals for sustained energy during the event

Glycemic Index of Common CHO

Low glycemic index

< 50

Moderate glycemic index

50-70

High glycemic index

>70

Glycemic Index and Exercise

The ideal meal immediately before exercise should provide CHO that sustain blood glucose levels while minimising increases in insulin release

By keeping insulin levels relatively unchanged, blood glucose should be preserved, fats should be mobilised and broken down and both liver and muscle glycogen stores spared for later use

Glycemic Index and Exercise Consuming high glycemic index foods

immediately before exercise results in rapid increases in blood glucose and insulin (hypoglycaemia)• Impairs functioning of central nervous system• Reduces free fatty acid mobilisation• Accelerates glycogen depletion

Consuming low glycemic index foods 45-60mins prior to exercise allows a slower rate of glucose absorption and supplies slow release glucose for use during exercise• These foods also avoid the insulin surge associated

with food that have a high GI

Fat

Stored as triglycerides (adipose tissue and skeletal muscle)

Triglycerides broken down into free fatty acids (FFA)• FFA broken down aerobically to provide

energy for movement

• Uses _____________ oxygen than CHO, therefore not the preferred fuel during exercise

Importance of Fat

Provides FFA that provide energy Produces more energy per gram than all other

nutrients (39kj per gram) Makes up to 50% of body’s everyday energy Carries fat-soluble vitamins A,D,E&K Contributes to taste, texture, aroma of food Provides protection for certain organs Helps produce cell membranes, skin hormones

and cholesterol

Fat During Exercise Recommended amount is 20-30% of a sporting diet Any more can cause health problems Not preferred to CHO because it is harder to break

down (uses more oxygen) When _____________ depleted during prolonged,

continual exercise fat becomes vital Athletes can teach their body to use fats first

(through aerobic training) in long events to keep glycogen stores in reserve for the high intensity end part of an event• Known as CHO/glycogen sparing

• Avoid ‘hitting the wall’

Protein Broken down into _____________ _____________ Makes up to 15% of diet Protein has several important functions:

• Formation and _____________ of body tissues, especially muscle tissue and cells

• _____________ and recovery of damaged such as muscle tissue

• Production of red blood cells, hormones, antibodies and enzymes

• Provision of emergency fuel source during exercise when CHO and fat stores are depleted

Protein During Exercise

Average diet supplies sufficient protein and essential amino acids to meet an athlete’s requirements

Some endurance athletes and power athletes believe more protein is required• Disadvantages:

• Less CHO in diet

• Excess fat intake associated with animal protein

• Increase chance of dehydration and constipation

Other Food Nutrients

Vitamins Minerals Fibre Fluid

Vitamins

Assist chemical reactions within the body Two types

• Fat soluble: stored in the body

• Water soluble: not stored in the body A balanced diet ensures adequate vitamin

intake No need for additional intake as these tend to

leave the body via urine Athletes should increase their intake via

increased food intake

Minerals

Important role in muscle contraction, nerve transmission, fluid balance, assisting enzymes in energy production and an important component of bone, muscle, skin and blood

Readily available in a well-balanced diet Two most important minerals

• Iron

• Calcium

Fibre

Eg: Important functions:

• Helps ensure a slow release of energy

• Helps to feel full

• Regulates bowel movements

Two types• Soluble:

• Insoluble:

Fluid

70% of our body is water Each day the body needs to replace 2 litres of

fluid• Not even accounting for sweating

Important functions• Transport energy, waster, hormones, antibodies

• Dilute waste products

• Lubricate surfaces and membranes

• Help regulate body temperature

• Involved in all chemical reactions in the body

Fluid Dehydration is a major cause of

_____________ Athletes must ensure fluid intake

compensates for sweat lost during exercise Dehydration leads to a drop in performance

and can be life threatening 300-400mL prior to exercise 400-1000mL per hr during exercise Sports drinks that contain CHO and

electrolytes are better during prolonged exercise