Читать книгу Eating for Sport - Shelly Meltzer - Страница 11

No matter what your sport, carbohydrate (foods rich in starches and sugars, see 50g carbohydrate list p17) is the critical fuel for optimal performance. Exercising muscles rely on carbohydrate as the main source of fuel. Therefore diets low in carbohydrate can lead to a lack of energy during exercise, early fatigue, loss of concentration and delayed recovery. All carbohydrate, once digested, are eventually converted into blood glucose or stored as glycogen in the liver and muscle for later use. Excess carbohydrate will be stored as fat.

Since the 1920s scientific studies have revealed the ergogenic properties of carbohydrates. Later studies showed that a relatively high carbohydrate intake appears to delay the onset of fatigue during endurance-type events. This refers to pre-event carbo-loading of 600–700g/day to maximize liver and muscle glycogen stores. Similarly, carbohydrate ingestion during exercise also delays the onset of fatigue by sparing liver glycogen, but the mechanisms of this effect seem to be governed by central regulatory functions rather than solely as a consequence of delaying an impending ‘energy crisis’.

There is also evidence that in high-intensity, intermittent exercise lasting less than one hour, carbohydrate loading and carbohydrate ingestion during exercise (30–60g/hr) appear to impart some neuro-protection from fatigue.

MACRONUTRIENT	ENERGY
Carbohydrate	17kJ/g (4kcal/g)
Protein	17kJ/g (4kcal/g)
Fat	38kJ/g (9kcal/g)
*Alcohol	29kJ/g (7kcal/g)

Energy content of macronutrients. *Although alcohol supplies energy, it is not available as a source of fuel during exercise and has little nutritional value (see pp68–69).

In the world of performance, carbohydrates are essential. Once ingested, they are turned into glucose and stored in the muscles and liver as glycogen.

In summary, all the evidence shows that carbohydrates have an important role before, during and after exercise. This may vary between individuals and the mechanisms are not completely understood. Ingesting carbohydrate during exercise is the most effective way of preventing hypoglycaemia (low blood sugar levels).