NUTRITION AND EXERCISE. FOOD FUELS Food is the source of energy for all cellular activity in the body. When we eat, food travels to the stomach and intestines.

NUTRITION AND EXERCISE

FOOD FUELS

Food is the source of energy for all cellular activity in the body.

When we eat, food travels to the stomach and intestines to be digested.

The digestive system breaks down the foodstuffs, absorbs the nutrients and transports wastes to the bowel.

Our food intake consists of 3 basic nutrients…. Carbohydrates (CHO) – fruits cereal, bread,

pasta and vegetables. The body’s preferred fuel source during exercise.

Fat – eg butter , margarine, cheese, oil, nuts. The body’s preferred fuel source at rest.

Protein – eg meat, fish, poultry. Makes little contribution to energy production during exercise. Mainly used for growth and repair.

Nutrients are carried, via the bloodstream surrounding the digestive system, to cells of the body.

Other essential dietary ingredients Water, minerals and vitamins are

also essential in the diet. However, CHO, Fats and Proteins

are the ONLY nutrients from food that form fuel for ATP resynthesis.

ATP resynthesis Only a small amount of ATP exists at the

muscles. ATP must be continually rebuilt or

resynthesised so that energy can be provided for longer periods of time.

This process occurs through the energy systems

The three energy systems

There are 3 pathways in the body that resynthesise ATP.There is the Aerobic System and two anaerobic systems called the Lactic Acid System and the ATP-PC System.

Fuels for each energy system

The ATP-PC system requires phospho-creatine (PC), which occurs and replenishes naturally with appropriate rest

PC will not increase with dietary supplementation

A balanced diet and healthy body will maintain PC levels

Fuels for each energy system

The Lactic Acid system requires glucose

The muscles (and liver) store glucose in the form of glycogen

Carbohydrates in food breakdown to glucose for blood transport

The Lactic Acid system may draw glucose from the blood or stored glycogen

Fuels for each energy system

The Aerobic system can use glucose/glycogen, fat or protein as fuel

Which System At rest, our demands for ATP are low and can be

met aerobically with little input from the anaerobic systems

As we exercise the demand for ATP increases and our oxygen intake cannot always keep up. This is where the anaerobic systems become more involved

For any sub-maximal activity of longer duration the aerobic system will supply most of the energy…

…But higher intensity efforts, required during that activity, will call on the anaerobic systems to be dominant

Food Fuels at rest.

At rest about two thirds of food fuel is contributed by Fats and about one third by carbohydrates (glucose). The contribution of protein is negligible.

The aerobic system is the major energy system at work because sufficient oxygen is available to the organs and muscles.

Food Fuels during exercise For exercise of short duration and high

intensity the anaerobic systems supply most of the energy and the food fuel used by the Lactic Acid System is the stored form of carbohydrate, glycogen.

For exercise of longer duration, at intensity below 85% of max effort, the aerobic system is the main supplier, with carbohydrates generally being the preferred fuel. If CHO stores are depleted, fats become the main fuel source for aerobic energy production.

Carbohydrate contribution Energy from muscle contraction stems from muscle

and liver glycogen. An average 80kg person can only store 100 grams of

glycogen in the liver and 400 grams in muscles around the body. This is enough to fuel a 25km run at moderate pace.

It is important to eat a CHO rich diet if preparing for an endurance event, to increase these glycogen stores.

Even though fats will produce more ATP per unit during aerobic energy production, CHO (glycogen) is preferred over fats as a fuel source during exercise. It requires less oxygen and still produces a high amount of ATP.

Fat Contribution

Fats are stored throughout the body in adipose tissue and in skeletal muscles as triglycerides.

Fats are transported in the blood as fatty acids

Fat contribution (cont) One fat molecule can produce up to 100 ATP (compared

to one glycogen molecule producing just 38 ATP), but its breakdown requires a lot more oxygen than glycogen.

This is why CHO is the preferred source of fuel during exercise – as intensity increases, oxygen is in more demand.

Approximately 50% of the body’s everyday energy production comes from fat. It becomes a very important source of energy when glycogen levels are low.

Endurance athletes train to improve their capacity for oxygen uptake so they can use fat more as a fuel source. That way they can “spare” glycogen for the anaerobic glycolysis required during high intensity efforts like surges and sprint finishes.

Protein contribution Protein forms the building blocks of tissue

growth and repair. All enzymes which speed up chemical

reactions are proteins. Protein is generally not required for aerobic

energy production under “normal” sporting circumstances

Protein is only used more for energy in extreme circumstances, such as high stress endurance events and starvation.

The Glycemic (GI) index The GI index is a ranking of carbohydrate based on

how quickly they breakdown to glucose and enter the blood stream.

CHOs that break down quickly have the highest GI index. The blood glucose response is fast and high.

CHOs that break down slowly, releasing glucose gradually, have the lowest GI index.

Low GI leads to a slower rise in blood glucose levels after meals and can prolong endurance performance.

Nutrients from food

Pre-exercise food

The ideal meal before exercise should provide carbohydrates that sustain blood glucose levels while minimising increases in insulin levels.

Consuming High GI foods immediately before exercise results in rapid surges in blood sugar and insulin - both detract from endurance performance.

Pre-Exercise food

A good preparatory meal 2 to 3 hours before competing will focus on Low GI foods and might include…

Muesli with

yoghurt Baked Beans on whole grain toast

OR

Low Fat milk or water would be good fluid intake

During Exercise food

High GI food is best during competition It helps to maintain normal blood sugar

levels and prolongs the availability of muscle glycogen

Unless the event is continuous for at least 90 minutes OR a field/court sport lasting at least 60 minutes nutrition during is largely unnecessary.

Hydration should be maintained though at around 200mls per 15-20 minutes

During Exercise food

During the event you need High GI intake

Recovery from exercise After exercise an athlete should intake

1.2 gram of High GI carbohydrate per kg of body mass each hour for at least 4 hours post exercise.

For at least the first 3-4 hours of recovery, this CHO intake will accelerate muscle glycogen recovery from the normal 5% to 7-8% per hour

Hydration needs to be also maintained

Food for Recovery 1.2 gram of High GI carbohydrate

per kg of body mass each hour for at least 4 hours post exercise.

Other Food Nutrients

Vitamins are important as they assist chemical reactions in the body (and help release energy from food)

Also particularly important for athletes are minerals, known as “electrolytes” (eg: sodium, potassium), which help maintain muscle contraction, nerve transmission, fluid balance and enzyme activity

Vitamins There are 14 vitamins divided into fat

soluble vitamins and water soluble vitamins.

Although not an energy source in themselves, they assist chemical reactions in the body that help break down food fuels.

They are also involved in red cell production, tissue repair and protein synthesis

Minerals There are 10 main minerals needed in

various amounts by the body. Minerals such as sodium and potassium play

an important part in muscle contraction, nerve transmission, fluid balance and assisting enzymes in energy production.

Iron (carrying of O2 in red blood cells) and Calcium (bone density and strength) are also important considerations in a well balanced diet.

Fibre Fibre is the part of the plant that is

not digestible. It helps ensure a slow release of

energy by slowing the release of sugar from the blood.

It helps the feeling of being full without extra kilojoules and regulates bowel motions

Fluid Over 70% of your body mass is water. Each day the body has to replace at least two

litres of water to replace what is lost (not including sweating)

Fluid serves many functions such as:

- transporting energy waste, hormones and antibodies- diluting waste products- lubricating joint surfaces and membranes- helping to regulate body temperature