Variations exist between endurance runners, with elite runners, depending on metabolic and anthropometric characteristics, having varying needs for carbohydrate consumption ranging from 50 to 70% of total calories (Schroder et al., 2008). These needs also change as periodization of training occurs (Schroder et al., 2008). Some data suggest that male athletes will meet recommended carbohydrate intake whereas female athletes, especially endurance, may not (Burke, Cox, Cummings, & Desbrow, 2001, Deuster et al., 1986). Before any recommendations on food planning can be made a nutritional assessment should be done for each athlete to discern specific nutritional needs and preferences (Campbell & Spano, 2011). There is interindividual differences in what carbohydrate sources athletes find palatable and tolerate without gastrointestinal distress. Given this, any recommendation should be trialed during training sessions to figure out what carbohydrate sources work best (Campbell & Spano, 2011).
It has been suggested that optimal carbohydrate intake for daily consumption in the endurance athlete range between 8-10 g/kg/day. Under normal rested conditions this is purported to preserve resting muscle glycogen levels to complete 60-90 of aerobic activity. However, for intense aerobic competition, other ways to maintain muscle glycogen stores must be used. These include precise nutrient timing and content during the prerace, interrace and post-race periods (Campbell & Spano, 2011). Additionally, the combination of carbohydrate with protein or amino acids may facilitate improved performance and recovery more than carbohydrate alone (Campbell & Spano, 2011). Below are examples of foods that could be used to enhance performance and recovery.
The prerace feeding plans can last between hours and days. In traditional carbohydrate loading an athlete would start carbohydrate depletion 3 to 4 days with intense training then a 3 to 4-day low-intensity training and carbohydrate repletion to supersaturate the muscle glycogen. Using this plan any carbohydrate source that the athlete enjoys is fine. For example, pastas, breads, rice, potatoes, bagels, carrots, walnuts, salmon, and peanut butter. A mixture of high carbohydrate foods with protein and small amounts fats will help restore glycogen stores. During this period some elite runners will require up to 12g/kg/day of carbohydrate (“Carbohydrate-loading Diet,” 2018).
It should be noted that a nutritious diet with sufficient carbohydrates sustain exercise at competitive levels alone (McArdle, Katch, & Katch, 2012). The recommendation for the traditional loading scheme is to have the athlete practice the technique in an incremental fashion before attempting the full loading schedule (Campbell & Spano, eds., 2011; McArdle, Katch, & Katch, 2012). The traditional loading scheme presents a problem as a byproduct of the technique is weight gain via water bound to glycogen molecules (Campbell & Spano, eds., 2011; McArdle, Katch, & Katch, 2012). If an athlete adds 500 grams of additional glycogen above normal storage they could retain about 48 ounces of water or 3 pounds (McArdle, Katch, & Katch, 2012). This causes a heavy feeling for some athletes and may interfere with performance, especially in the uninitiated runner. Additionally, during depletion the ability to train hard is negatively impacted, mood states can change, vitamin deficiencies may occur, and there may be a loss of some lean body tissue (McArdle, Katch, & Katch, 2012).
A non-depletion loading for events exists with a well-nourished and rested runner consuming 10g/kg/day of carbohydrates from 1 -3 days prior to the event (Campbell & Spano, 2011) with similar foods as above. High versus low glycemic carbohydrates are not as much of a concern during this period as training intensity is low and the race is days away allowing for adequate digestion.
In the period of 2-4 hours before an event, it is suggested that single carbohydrate meals can increase muscle and liver glycogen stores. Recommendations of 1-4g/kg of carbohydrate several hours prior to the event is sufficient. Early morning starts where sleep may interfere with a 4-hour feeding time require special attention. In this case, lower carbohydrate intake prior to the event with working hard at ingesting the carbohydrates needed during the beginning period of exercise may be important (Campbell & Spano, 2011). The alteration of feeding based on the glycemic index has produced mixed results (Campbell & Spano, 2011; MaArdle, Katch, & Katch, 2012).
It has been suggested that consuming simple sugars before exercise causes blood sugar to rapidly rise and insulin levels to surge. This results in a cascade including rebound hypoglycemia, decreased fat catabolism, and premature depletion of glycogen reserves (MaArdle, Katch, & Katch, 2012). Consuming foods that have low-glycemic response theoretically should reduce the risk of this cascade. Foods that contain higher fiber slow absorption and extend the release of carbohydrate over time (MaArdle, Katch, & Katch, 2012). Given the above, such foods may include (1) oatmeal with dried fruit, (2) non-fat yogurt mixed with some fruit and granola, and (3) whole-grain pasta.
During the event
Carbohydrate oxidation rates during prolonged moderately intense exercise are about 1g/min. This is true for high, moderate and low glycemic feeding and when feeding schedule is altered (Campbell & Spano, 2011). Different types of carbohydrates have different digestive transport mechanisms and combining several different carbohydrates may increase absorption rate per unit of time. Recall that for a single carbohydrate the absorption rate is 1g/min. When a mixture of ingested sucrose and glucose was assessed during exercise absorption rates increased to 1.2g/min, a 21% increase (Campbell & Spano, 2011). A combination of maltodextrin and fructose resulted in an increase to 1.5g/min which is 40% more than maltodextrin alone (Campbell & Spano, 2011). Clearly providing more then one carbohydrate source is better than a single source. During the event, the ingestion of a 6-8% carbohydrate solution drinking 8-16 oz every fifteen minutes using a combination of glucose, sucrose, maltodextrin, and/or small amounts of fructose has been shown to be beneficial at maintaining blood glucose (Campbell & Spano, 2011). It should be noted that high levels fructose can cause gastric distress and should be used in moderation, if at all. Additionally, a carbohydrate to protein ratio of 4:1 has been shown to improve endurance (acute and subsequent) and reduce muscle damage (Campbell & Spano, 2011). Inclusion of branch chain amino acids to the solution may help. Protein content should not be greater than 2gs/kg. As a supplement during an event the runner can use gummies or raisins for carbohydrate replenishment.
Glycogen recovery is a key consideration for any athlete. The most consistent finding in the sports literature is that endurance athletes who ingest 1.5g/kg carbohydrate within 30 minutes of exercise have greater muscle glycogen synthesis (Campbell & Spano, 2011). Studies agree that both liquid and solid sources of carbohydrate work well. It has also been noted that higher glycemic foods should be avoided and lower glycemic foods included due to the rapid digestion (Campbell & Spano, 2011). It is also recommended that an athlete can consume high amounts of carbohydrates over a 4 to 6-hour period (0.6 -1.2g/kg/hr) after exercise to ensure adequate muscle and liver glycogen stores (Campbell & Spano, 2011). Combining carbohydrate and protein during recovery may help with the restoration of muscle glycogen, reduce muscle damage and preserve immune function (Campbell & Spano, 2011). Ultimately the carbohydrate content is the most important factor in glycogen replenishment (Campbell & Spano, 2011). Given the above foods that could be recommended are for the post 30-minute period (1) low-fat chocolate milk (27 grams carb), (2) organic fruit of life bar (42 grams carbs), (3) large banana (31 grams carbs) or a (4) smoothie with fruits (70 grams carbs). For the period of 1 to 6 hours progressively moving from high glycemic foods to lower glycemic foods.
Burke, L. M., Cox, G. R., Cummings, N. K., & Desbrow, B. (2001). Guidelines for Daily Carbohydrate Intake. Sports Medicine, 31(4), 267-299. doi:10.2165/00007256-200131040-00003
Campbell, B. I., & Spano, M. A. (2011). NSCA’s guide to sport and exercise nutrition. Champaign, IL: Human Kinetics.
Carbohydrate-loading diet. (2018, February 24). Retrieved from https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/carbohydrate-loading/art-20048518
Deuster, P. A., Kyle, S. B., Moser, P. B., Vigersky, R. A., Singh, A., & Schoomaker, E. B. (1986). Nutritional survey of highly trained women runners. The American Journal of Clinical Nutrition, 44(6), 954-962. doi:10.1093/ajcn/44.6.954
MaArdle, W. D., Katch, F. I., & Katch, V. L. (2012). Sports and exercise nutrition (4th ed.). Philadelphia, PA: Lippincott Williams and Wilkins.
Schroder, S., Fischer, A., Vock, C., Bohme, M., Schmelzer, C., Dopner, M., . . . Doring, F. (2008). Nutrition Concepts for Elite Distance Runners Based on Macronutrient and Energy Expenditure. Journal of Athletic Training, 43(5), 489-504. doi:10.4085/1062-6050-43.5.489