The relationship between nutrition and physical activity.

Good nutrition and adequate physical activity are important throughout our lives. The amount of exercise an individual gets, affects their nutritional status and overall health. In turn, diet and nutritional status can influence exercise performance.

A good level of fitness reduces the risk of chronic diseases, such as cardiovascular disease and obesity. Whether your goal is o maintain your health or to compete in an athletic event, good nutrition provides a launching pad from which physical fitness can be improved.

The right mixture of the energy-yielding nutrients Carbohydrate, fat and protein (along with adequate micro-nutrients and water) enhances the performance of the body.

Energy for activity

Carbohydrates, fats and proteins are the fuel sources for the body, but before they can be used to fuel activity, their energy must be converted into high energy compound adenosine triphosphate or ATP. ATP is the immediate source of energy for all the body’s functions. In a resting muscle, there is enough stored ATP to sustain activity for a few seconds. As the ATP in the muscle is used, enzymes break down another high-energy compound called Creatine phosphate (CP) to replenish the ATP supply. As with ATP, the amount of CP stored in the muscle at any time is small. During the first 10-15 seconds of exercise, the muscles use the energy from the ATP and CP that is stored there, but activity of longer duration requires the body to replenish ATP from the metabolism of energy-yielding nutrients.

Carbohydrates, fats and proteins are all used to produce ATP when oxygen is available. When no oxygen is available, only carbohydrates can be used; although carbohydrates produce ATP rapidly, it is not used efficiently. The availability of oxygen in the muscle cells is determined by how quickly the heart can pump oxygen via the blood to the working muscles.

EXERCICE DURATION SOURCE OF ATP

100m 10 secs Creatine phosphate

200-800m 20-120 secs Glucose

Marathon 2+ hrs Fatty acids and glucose

Producing energy from carbohydrates

The carbohydrates fuel used for exercise is glucose. Glucose is found in the bloodstream and is stored as glycogen in the muscles and the liver. The transformation of glucose into energy occurs in one of the two ways: with oxygen (aerobically) or without oxygen (anaerobically). Glucose burned with oxygen produces carbon dioxide (a waste product), water, ATP and heat. Glucose burned without oxygen produces lactic acid, ATP and heat.

Glucose is converted to energy in muscle cells which have mitochondria (tiny bodies found inside most cells) so they can process glucose with oxygen. Being able to turn glucose into energy without oxygen ( i.e. when exercising strenuously) is one of the advantages of using carbohydrates as fuel. The disadvantage is that the lactic by-product can lead to muscle soreness.

Producing energy from fats

Fats can only be used as energy source when oxygen is present (when working aerobically). They provide a lightweight, energy dense fuel supply. The process of burning fat for energy is called lipolysis. During exercise, the triglycerides in adipose tissue and in muscle fibres are broken down into acids and glycerol.

Fatty acids are released into the blood and taken up by the muscle cells. Inside the muscle cells, fatty acids are transported to the mitochondria to produce ATP.

The energy yield of fats is 9 kcal per gram. Carbohydrates provide 4 kcal per gram, so fats are more economical source of fuel.

Producing energy from proteins

Proteins are broken down into amino acids, which can also be used to produce ATP when oxygen is available. For most exercise protein contributes only a small percentage of the energy used. It becomes an important source of energy only when exercise continues for many hours.

Endurance exercise increases the use of amino acids, both as an energy source and to help maintain blood glucose levels. If amino acids are in excess of the body’s biological requirements, they are converted into glycogen or fat so that they can be used for energy metabolism. Burning proteins for fuel produces carbon dioxide, water, ATP, urea, and ammonia. Proteins provide 4 kcal of energy per gram (the same as carbohydrates).

Which fuels are used and when.

As a general rule, the body burns either fat or carbohydrates depending on the intensity of the activity. However, the body does not completely stops using one fuel source to use other. The intensity and duration of exercise and the conditioning of the exerciser can affect the contributions that carbohydrates and fats make as fuels for energy production. Fat utilisation, in turn, affects ow long exercise can continue before fatigue sets in. while rest, the cardio-respiratory system is able to deliver enough blood and oxygen to the muscles to allow aerobic metabolism of fatty acids. But during exercise, the delivery of oxygen to tissues can become limited, causing the muscle cells to rely (at least partially) on the anaerobic metabolism of glucose. In general, the more intense the exercise, the more muscles rely on glucose to provide energy.

Source: active iq