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Carbohydrates

The main function of carbohydrates is to serve as an energy fuel for the body. Carbohydrates are carbon and water based molecules which range in size and are found in most plant foods, mainly fruits and grains. There are many different types of carbohydrates ranging from simple sugars such as glucose and fructose to long polysaccharides, which may contain many simple sugars. Regardless of the size, once it has been consumed it is broken down into the smallest unit, a glucose molecule, in order to be used by the body.

Disaccharides

  • Sucrose = Fructose + Glucose
  • Lactose = Glucose + Galactose
  • Maltose = Glucose + Glucose

Monosaccharides

  • Glucose
  • Fructose
  • Galactose

Complex Carbohydrates (Starches)

Amylose Average chain length of 600 glucose residues
Amylopectin Average chain length of 6000 glucose residues

Dietry Fibre

Soluble Absorbs water, delays the absorption of sugar and binds bile salts
Insoluble Binds to water and has a bulking affect which aids and improves the efficiency of the action of the gut and colon and the movement of nutrients and waste products through the digestive tract

Glucose, Glycogen and Performance

Glucose is transported into muscles and other tissues where broken down to create energy. When glucose is not needed immediately for energy, its stored into muscle and liver in long chains called glycogen. Skeletal muscle favours glucose to replenish glycogen while the liver favours fructose. Glycogen stores in the liver are used to fuel organs such as the brain and glycogen stores in the muscles are used to fuel muscle activity. The body's capacity for storing glycogen is limited. Once the glycogen stores are replenished it is possible for excess glucose to be converted into fat and stored for later use.

Because carbohydrates can be stored around the body as fat, carbohydrates have developed a bad name, and many athletes strive to reduce their intake of carbohydrates in order to avoid gaining fat, however extreme carbohydrate restriction is counter-productive and potentially dangerous for athletes. Since muscle and liver glycogen stores are limited, a low carbohydrate diet will not provide you with the energy you need to perform a hard workout. In addition since carbohydrate provides essential fuel for the immune system, low carbohydrate diets make you more susceptible to colds and infection.

Consuming carbohydrates around training times can have positive effects on muscle growth and performance, however when consumed in excess carbohydrates can have negative effects on the body. When dietary carbohydrate is high, blood insulin levels raise and after many years your body begins to resist the hormone. This results in higher blood insulin levels which can lead to fat storage around the body and increased risk of developing (type2) diabetes.

Glycemic Index

The glycemic index is a method of categorising foods by their effect on blood glucose levels. A food with a low glycemic index produces a mild, sustained increase in glucose levels. A food with a high glycemic index produces a large glucose spike. At one time conventional wisdom held that foods containing mostly simple sugars had a high glycemic index and those containing mostly complex carbohydrates had a low glycemic index however there are some exceptions to this rule. Generally whole grains have a lower glycemic index than refined grains, high fibre foods have a lower glycemic index than high fibre foods, and foods containing high amounts of protein and fat have a lower glycemic index than foods with small amounts of protein and fat, as they slow down the absorption process. The general perception is that high glycemic index foods are a bad nutritional choice because they cause insulin spikes and also result in fatigue and overeating due to blood sugar crashes, however their powerful effect on insulin also makes high glycemic index sugars valuable during and immediately after exercise. They not only provide energy but also through their action on insulin help lower blood cortisol levels and turn on cells anabolic machinery.

Another overlooked benefit of carbohydrate during extended exercise is that they help with the metabolism of fat. The muscle cell has a metabolic priority system when it comes to nutrients it uses for energy. For short exercise bouts such as resistance exercise, carbohydrate is the primary nutrient used. During extended exercise the muscles tend to rely on fat stores as its source of energy. But carbohydrate is still a required nutrient in order to drive the use of fat for energy. After 45 minutes of exercise protein primarily BCAA's can provide up to 15% of the muscles total energy needs.

Summary

  • Simple carbohydrates are broken down rapidly and are useful when energy is needed rapidly.
  • Complex carbohydrates are broken down more slowly and found in potatoes and pastas.
  • Fibres delay the absorption of sugar and can help keep blood sugar levels more stable as well as having positive effects on digestion
  • Carbohydrates have a glycemic index which is a measure of its impact on blood sugar levels
  • Glycogen is our body's main store of carbohydrate and can be found in the liver and muscles Excess consumption of carbohydrate can lead to fat storage and raised blood insulin levels which over time can have negative effects on health

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