However, in situations where maximal glycogen storage is desirable or the athlete must meet the fuel bill of prolonged exercise sessions, carbohydrate needs are higher and more specific. Studies have determined the absolute requirement of the muscle for carbohydrate in these situations (see Table). However, some sports nutritionists have continued to describe the increased needs for carbohydrate in terms of energy ratios - for example, an endurance athlete should eat 70% of energy from carbohydrate.

We think, in these specific situations, that it is best to set definite carbohydrate intake goals for athletes, scaled to their body size and therefore, their muscle mass. A guideline to consume 7-10 g of carbohydrate per kilogram body mass (BM) is not only tailored to the muscle's needs, but is more "user-friendly" for the athlete. An athlete can calculate a definite carbohydrate target in grams, and use food tables or information on food labels to plan meals to reach this goal. Even better, the athlete can see a sports dietitian for advice to further narrow this target range according to their specific situation, and have an individualised meal plan fitted to their needs.

And although total amounts of carbohydrate in grams may be a better guide, they still must be regarded with some flexibility. In all areas of nutrition, judgements of adequacy or deficiency cannot be made from a single piece of evidence. This is particularly the case when the evidence comes from a food record or another type of self-reported dietary assessment. Athletes, just like sedentary people, are not necessarily accurate in describing their real food intake - and most often they underestimate or under-reporte their true intake of food and nutrients.

Dietary assessments should be done by an expert such as a sports dietitian, who will work with an individual athlete to collect different sources of information related to their nutritional needs and eating patterns. Specific information about the athlete's training load and their ability to recover between sessions may help to fine- tune carbohydrate intake targets. It is important, particularly in terms of judging everyday carbohydrate intake, to regard guidelines as an approximation rather than a fixed rule. Generally, though, for athletes who have an important or increased need for carbohydrate needs, it is both more reliable and more practical to set guidelines in terms of a fixed amount of carbohydrate, rather than an energy percentage.