Timing of Eating and Exercise (Technical)

The role of nutrition in regard to physical activity and athletic performance is of high importance for all athletes. There are many aspects to consider in the realm of sports nutrition, and an important area is the timing of food and fluid consumption around exercise. The research in this area points to several specific guidelines to assist athletes in optimizing their performance by not only consuming the proper nutrients, but also consuming them in the appropriate time frame around exercise.

In general, nutrition guidelines for athletes for each of the macronutrients are as follows: 6-10 grams carbohydrate per kilogram body weight per day, 1.2- 1.7 grams protein per kilogram body weight per day, and 20% to 30% of total daily energy from fat (Rodriguez et al. 2009). For maximum benefit, spacing the consumption of each of these nutrients appropriately is essential. Each of these nutrients plays a specific role in regard to physical activity.

Carbohydrates are the body’s preferred source of energy, and consumption of carbohydrates is beneficial in supporting activity. Ingesting carbohydrates assists with the maintenance of blood glucose levels during exercise, and also replenishes muscle glycogen (the storage form of carbohydrates in the body; Dunford and Doyle 2012). The specific recommendations for total daily carbohydrate intake based on training load and type of exercise are shown in Table 1 (Nutrition Booklet 2010).

Table 1.

Training Load Type of Exercise Carbohydrate Intake Targets (g/kg body mass)
Light Low intensity or skill-based activities 3-5 g/kg/d
Moderate Moderate exercise program (i.e. ~1 hour per day) 5-7 g/kg/d
High Endurance program (e.g. 1-3 hours per day of mod-high-intensity exercise) 6-10 g/kg/d
Very High Extreme commitment (i.e., at least 4-5 hours per day of mod-high intensity exercise) 8-12 g/kg/d

Protein has many unique functions in the body, however protein can only be used for these important roles when there is sufficient caloric intake from carbohydrates and fat (Dunford and Doyle 2012). Though the body can use protein for energy, consuming sufficient carbohydrates will provide a protein-sparing effect. This means that protein will not be converted to energy, and can instead be used to carry out its other important functions in the body, such as tissue maintenance and repair, nutrient transport, muscle protein synthesis, and so forth (Gropper et al. 2008).

Fat is a necessary nutrient for athletes, and together with carbohydrate acts as an important energy source for moderate-intensity exercise. Fat provides essential fatty acids, and allows absorption of fat soluble vitamins (Mahan and Escott-Stump 2008). Careful consideration is required to allow sufficient but not excessive fat intake. Of particular concern is that fat slows gastric emptying and takes longer to digest than either carbohydrates or protein, so the timing of fat intake around exercise is a key factor to consider in meal planning (Dunford and Doyle 2012).

As has been demonstrated, each macronutrient plays a key role in exercise performance, and the timing of intake for each of these nutrients is an important consideration. The specific recommendations for food and fluid intake within each time frame surrounding exercise are detailed below.

Before Exercise

In sports nutrition, the recommendations for nutrition prior to exercise generally refers to the time frame approximately four hours before exercise begins (Dunford and Doyle 2012). Though overall nutrition status plays a role in athletic performance, this time frame has the most immediate impact on the upcoming bout of exercise. Fueling before exercise is important as improvement in exercise performance has been shown when food is ingested prior to exercise, as compared to exercising in a fasted state (Maffucci and McMurray 2000, Jentjens et al. 2003, Mosely et al. 2003).

There are several purposes to fueling the body appropriately before exercise. Though maximizing performance is the key benefit, avoiding gastrointestinal distress during exercise, maintaining blood glucose levels, and avoiding excessive or inadequate hydration are other purposes for fueling properly prior to exercise. Though fatigue during exercise cannot be prevented, the onset of fatigue can be delayed with proper fueling before exercise (Dunford and Doyle 2012). In order to accomplish these purposes, it is recommended that the pre-exercise meal or snack should be of a particular composition. In regard to macronutrients, it should be high in carbohydrates, low in fat, and moderate in protein. Other important considerations include low fiber options and adequate fluid consumption (Rodriguez et al. 2009).

The total amount of food consumed before exercise will be determined by the time between eating and the onset of exercise. The general guide is that larger meals can be consumed when there is a greater time gap between eating and exercise, whereas smaller amounts of food should be consumed if eating and exercise are in close proximity. In terms of carbohydrate, it is often recommended that 1-4 grams carbohydrate per kilogram body weight be consumed 1-4 hours prior to exercise (1 gram per kilogram if 1 hour prior, 2 grams per kilogram if 2 hours prior, etc.; Dunford and Doyle 2012). The key to pre-exercise feedings is that the athlete should start the exercise bout without feeling hungry, but also without food in the stomach that is undigested. As each athlete will tolerate various foods differently, the most important consideration with pre-exercise meals is that they should be familiar to the athlete, and new foods should be tried during training sessions before being used in competition settings (Rodriguez et al. 2009).

Considerations in regard to fluid intake include achieving sufficient hydration, while allowing sufficient time for fluid voiding prior to exercise. At least four hours prior to exercise it is recommended that water or a sports drink be consumed in the amount of approximately 5 to 7 milliliters per kilogram body weight (Rodriguez et al. 2009).

4673-clocks-81During Exercise

The ingestion of nutrients during exercise becomes of greatest importance during prolonged exercise. The purposes of fueling during exercise include maximizing performance, delaying fatigue, managing fluid and electrolyte balance, and avoiding gastrointestinal distress (Dunford and Doyle 2012). The composition and timing of the pre-exercise meal contributes to the determination of proper fueling during exercise. Of the body of research available, the two aspects of most importance for consumption during exercise include fluid and carbohydrate replacement.  For exercise bouts lasting less than 45-60 minutes, water is generally sufficient. However, endurance performance has been shown to be benefited with sports beverages that contain 6-8 percent carbohydrate, and this composition is appropriate for ingestion during exercise (Nicholas et al. 1995, Jeunjendrup et al. 1997, Sugiura and Kobayashi 1998). For events lasting longer than one hour it is recommended that carbohydrate intake be in the range of 30-60 grams carbohydrate per hour, or 0.7 grams carbohydrate per kilogram body weight per hour (Coggan and Coyle 1991, Currell and Jeukendrup 2008).

Though total carbohydrate ingestion is important, the type of carbohydrate consumed is another relevant consideration. Evidence suggests that fructose alone may not be tolerated or used as effectively as other forms of carbohydrate, such as mixtures of glucose and fructose, other simple sugars, and maltodextrins (Coggan and Coyle 1991). Carbohydrates may be obtained from food, gels, or sports beverages, the latter option also providing needed fluid. If carbohydrates are consumed from food or gels, water should also be consumed to maintain hydration status during exercise.

It is beneficial to begin carbohydrate ingestion shortly after beginning exercise, rather than waiting until later in the exercise bout. Additionally, the timing of carbohydrate consumption during exercise has been shown to be more effective when ingested every 15 to 20 minutes throughout activity rather than as a single bolus (McConell et al. 1996, Rodriguez et al. 2009).

In regard to fluid intake during exercise, the goal is to prevent dehydration, particularly fluid losses in excess of two percent of body weight. The regimen for fluid replacement should be determined based on individual sweat rate, environmental conditions, opportunities to drink, and the duration and intensity of exercise (Sawka et al. 2007). The American College of Sports Medicine has not established specific general recommendations for fluid replacement during exercise, as these general guides would likely be inappropriate for many situations and could lead to significant under- or over-consumption of fluid, which could have detrimental effects (Sawka et al. 2007).

After Exercise

The significance of the post-exercise meal is determined largely by the length of time until the next exercise bout, as well as the duration and intensity of activity. The purpose of the meal after exercise is to replenish glycogen stores, repair muscle protein, replace fluid and electrolyte losses, and aid in overall recovery (Dunford and Doyle 2012).

The timing of the post-exercise meal in regard to replenishing glycogen stores is of most importance if the next exercise bout will occur in twelve hours or less, however the period immediately following exercise is a time frame when the body is best positioned to restore glycogen stores at the highest rate (Dunford and Doyle 2012). Delaying carbohydrate intake can significantly reduce glycogen synthesis (Ivy 1998). In light of this, it is generally recommended that carbohydrates be consumed within 30 minutes after exercise and that 1.5 grams carbohydrate per kilogram be consumed in the first hour following exercise (Ivy et al. 1998, Dunford and Doyle 2012). In regard to the type of carbohydrate, fructose alone is less effective than either glucose or sucrose (Blom et al. 1987).

Other macronutrient considerations do not necessarily impact the rate of glycogen synthesis, however they may have other benefits. Adding protein as part of a meal after exercise may be beneficial in regard to muscle protein repair (Rodriguez et al. 2007). In order to increase the rate of muscle protein synthesis after exercise, it is requisite to consume protein in the period following exercise (van Loon et al. 2013). In regard to specific amounts of protein and a specific time frame for protein ingestion surrounding exercise, additional research is required in this area (van Loon et al. 2013).

In regard to fluid needs post-exercise, recovery time is once again the key. If recovery time is not limited normal meals, snacks, and water intake should be sufficient to replenish fluid that has been lost. In situations where recovery time is limited, or there is excess dehydration, 1.5 liters of fluid for each kilogram of body weight lost should be consumed (Sawka et al. 2007). Body weight lost can be determined using pre- and post-exercise weighing. It is preferable to drink the recommended amount over time rather than as a larger bolus to assist in rehydration(Wong et al. 1998, Kovacs et al. 2002).

Though post-exercise nutrition recommendations may be difficult to implement due to other demands and factors (sleep due to fatigue, returning to school or work after training, decreased appetite, etc.), this is a critical time to replenish nutrient stores and set up properly for the next bout of exercise (Dunford and Doyle 2012).

Conclusion

In sum, when attempting to meet nutrition needs the timing of eating surrounding exercise is an important consideration. Appropriate meal timing and composition before, during, and after exercise can assist in improving athletic performance. 

By: Jamie Saunders, University of Utah
Jamie Saunders has always been interested in the area of nutrition and wellness. Saunders graduated from Southern Utah University with a Bachelor’s degree in Human Nutrition, and from the University of Utah’s Coordinated Master’s Program in Dietetics, with an emphasis in Sports Dietetics. She is a Registered Dietitian and currently works as the Outpatient Dietitian for the University Health Care’s South Jordan Health Center.

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Articles by Jamie Saunders.

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