· Index  Carbohydrate Intake Targets for Athletes:  Grams or Percent?
	Louise Burke, Australian Institute of Sport, Canberra, Australia

Using different terminology to educate athletes about their carbohydrate intake goals interferes at times with the interpretation of studies on carbohydrate and sports performance, and may cause athletes to have their diets unfairly criticized.  Nutrition guidelines for the community express carbohydrate intake goals in terms of the percentage of energy that should be consumed from carbohydrate.  This works because the message is general and the emphasis is on a relative change in fat and carbohydrate consumption.   When the muscle fuel needs of an athlete are moderate, adequate carbohydrate intake should be provided by a diet that meets these guidelines for healthy eating.  In most Western countries this message is to increase carbohydrate intake to at least 50-55% of energy.

However, in situations where maximal glycogen storage is desirable and/or the athlete must meet the fuel bill of prolonged exercise sessions, carbohydrate needs become more specific.  In these cases, the muscle has an absolute requirement for carbohydrate (see Table below).  Therefore, it is preferable to set definite carbohydrate intake goals for athletes, scaled to take the size of the muscle mass into account (i.e., the athlete's body mass).  The guideline to consume 7-10 grams of carbohydrate per kilogram body mass is not only considerate of the muscles needs, but is also user-friendly.  It is relatively easy to use a ready reckoner of the carbohydrate content of foods to add up the fuel provided by a meal or a diet - for example, to reach a target amount of 50 g snack after training, or a daily intake of 400-600 g.  It takes far more nutritional expertise to imagine what a dietary ratio of 50% or 60% or 70% carbohydrate looks like on a plate.  With the advice of a sports dietitian, an athlete should be able to narrow their carbohydrate intake targets to specific levels for specific occasions.

The absolute amount of carbohydrate required for optimal glycogen synthesis is greater than the typical intakes of most people, including athletes.  And it may require an athlete not only to eat more carbohydrate (in grams), but to devote more of their total energy intake to fuel foods to do so.  Typically, athletes need to earmark 50-70% of their energy intake to meet their carbohydrate needs.  This is a wide range, because in real life the total energy needs and the muscle fuel needs of an athlete are not always synchronized.  The "perfect" carbohydrate:energy ratio cannot be fixed.  Athletes who have large muscle mass and heavy training programs usually have very high energy requirements.  For these athletes, total intakes of 800-1000 grams of carbohydrate representing 8-10 grams per kilogram of body mass may be consumed from only 45% of their energy budget.  Other athletes may need to devote 70% of a restricted energy budget to achieve a carbohydrate intake of even 6-7 grams per kilogram.  This situation is particularly common in female athletes and others whose main dietary concern is to maintain lower body fat levels than seems natural.

There is an unfortunate tendency of those working with athletes to regard carbohydrate intake guidelines as rigid. Many judge the fuel intake of an athlete or a group of athletes to be deficient or inadequate based on the percentage of energy derived from carbohydrate.  Some sports nutrition guidelines, even from recognized bodies such as the American Dietetic Association, maintain the confusion because they set their dietary guidelines for athletes based on energy ratios.  However this is inappropriate if the goal is to judge fuel intake, and this doesn't track closely with total energy needs.  In the first situation described above, an athlete might be consuming a high total intake of carbohydrate, adequate to meet their fuel requirements.  However, they will be judged to be following a low-  or moderate-carbohydrate diet from the perspective of energy ratio. This often happens in the assessment of the diets of individual athletes, but has also led to some questionable interpretations of research data.  Some studies have exposed athletes to so-called high or moderate (low) carbohydrate diets and compared metabolic and performance outcomes.  They have found no differences between responses to the diets and concluded that high carbohydrate diets are not important for athletes.  However, their moderate carbohydrate diets (40% carbohydrate) may have provided reasonably large amounts of carbohydrate, thanks to a high total energy intake.  So, even the moderate carbohydrate diet met the fuel needs of the athlete. A high carbohydrate diet (80% of energy) may be superfluous for this group.

Although total amounts of carbohydrate may be a better guide for assessing or setting goals for an athlete, they still must be regarded with some flexibility.  In all areas of nutrition, judgments of adequacy or deficiency cannot be made from a single piece of evidence, particularly when it comes from a food record or another dietary survey tool.  Dietary survey methods suffer from many errors of reliability and validity which generally lead to an underestimation of true dietary intake.

A judgment of adequate or inadequate carbohydrate intake in an individual athlete can only be made by assessing overall nutritional goals and nutrient needs from a number of sources of information.   Specific information about an individual's training load and 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.   For athletes who have important or increased carbohydrate needs, it is both more reliable and more practical to set guidelines in terms of a fixed amount of carbohydrate, rather an energy percentage.

Summary of carbohydrate intake goals for the athlete
Goal	Carbohydrate Intake Target
5-6 hours of moderate intensity exercise, extremely prolonged and intense exercise.  Very high total energy requirements, daily muscle glycogen recovery, and continued refueling during exercise. (Tour de France cyclists)	10-12+ g/kg daily
To maximize daily muscle glycogen recovery in order to enhance prolonged daily training, or "load" the muscle with glycogen before a prolonged exercise competition	7-10g/kg daily
To meet fuel needs and general nutrition goals in a less fuel-demanding program - for example, < 1 hr of moderate intensity exercise, or many hours of predominantly low intensity exercise.	5-7 g/kg daily
To enhance early recovery after exercise, when the next session is less than 8 hrs away and glycogen recovery may be limiting.	1g/kg+  soon after exercise, and continued intake over next hours so that a total of ~1g/kg/2hrs is achieved in snacks or a large meal.
To enhance fuel availability for a prolonged exercise session (1 hr or longer)	1-4 g/kg during the 1-4 hours pre-exercise.
To provide an additional source of carbohydrate during prolonged moderate and high intensity exercise, particularly in hot conditions or where pre-exercise fuel stores are sub optimal.	30-60 g/hr in an appropriate fluid or food form

References

Hawley, J.A. and Burke, L.M. (1998). Peak Performance:  Training and Nutritional Strategies for Sport. Sydney: Allen and Unwin.