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even in competition preparation when these other nutritional goals are of lower priority, it appears advantageous to eat a variety of carbohydrate-rich foods to meet carbohydrate intake goals. It has been noted from a review of several laboratory studies of carbohydrate loading that when athletes are fed 'loading' diets in which the additional carbohydrate is supplemented from a single food source, the increase in glycogen above the athletes' control diet appears less than that attained from a high-carbohydrate diet of mixed origin (9). Whether this is a real effect requires further investigation; it is possible that reliance on a single food in a diet can lead to an underestimation of total carbohydrate intake, due to the compounding of inaccurate food composition data or malabsorption of the food.
Chocolate Bars and 'Fuelling Up'
Chocolate bars offer a compact and enjoyable source of carbohydrate for an athlete who has high carbohydrate requirements. They may provide a useful part of a 'fuelling up' programme, particularly as a portable snack that requires minimal preparation or storage facilities. However, the value of a varied food intake should be promoted, particularly in the everyday eating patterns of athletes in heavy training.
Studies have shown that eating a large, carbohydrate-rich meal (> 200 g carbohydrate) in the 4-hour period before exercise promotes endurance (10) and enhances the performance of a time trial undertaken at the end of a prolonged exercise session (11, 12). Pre-exercise meals may enhance carbohydrate availability during situations of endurance exercise by increasing muscle and liver glycogen stores (13), or by providing a source of glucose in the gut for later release. This may be particularly important for exercise undertaken in the morning after an overnight fast, when liver glycogen stores are likely to be depleted.
Guidelines for pre-exercise meals need to take into account gastrointestinal comfort as well as the potential for enhancing body carbohydrate stores. In some cases, an athlete may need to eat prior to a prolonged work-out or competition in order to prevent hunger during the subsequent exercise session. However, in all cases the athlete must ensure that such pre-exercise intake does not cause excessive fullness, or result in gastrointestinal discomfort and upsets during exercise. Excessive stomach fullness caused by the ingestion of large volumes of fluid before intense exercise is not only associated with gastrointestinal problems, but also with impairment in exercise performance (14). This presumably also applies to the excessive intake of solid foods, and to the intake of meals close to
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