Nutritional Strategies for Endurance Athletes: Sustaining Energy and Performance

Participation in endurance sports has continued to increase, with over 3.5 million athletes worldwide identifying as endurance athletes. Endurance athletes include but are not limited to runners, cyclists, triathletes, mountain bikers, cross-country skiers, and swimmers.  Nutrition plays a critical role not only in optimal performance during a race event but also in recovery and maximizing training outcomes.

Sports nutrition is not a “one size fits all” approach, with endurance athletes often needing to work and plan alongside coaches and practitioners to ensure their macro- and micro-nutrient needs are being met to best respond to their training and perform well on race day. Tailored nutrition strategies are a key factor in sustaining energy, mental focus, and mood while also enhancing athletic performance.

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Understanding the Nutritional Needs of Endurance Athletes 

When it comes to meeting the nutritional demands of various endurance sports, it’s not just about the right food choices. Athletes also need to consider optimal meal timing and the amount needed to meet their training needs, as well as fluid and food intake needs during longer-duration training sessions or races. While nutrition strategies can be used strategically during training to help prepare for race days, generally speaking, endurance athletes need to emphasize carbohydrate intake, as prolonged low carbohydrate intake can lead to fatigue and performance deficits, as well as an increased injury risk.  

Swimming, which requires high aerobic and anaerobic training for both strength and technique, has higher caloric needs for both carbohydrates (6-12 g/kg body weight) and protein (2g/kg bodyweight) and may require a slightly higher fat content than runners (greater than 20-25% caloric content of diet). Endurance runners have historically consumed higher carbohydrate diets, though more recently awareness is growing around the importance of emphasizing protein intake as well to meet training needs and maintain muscle mass.  Low protein intake may cause fatigue earlier in race times and lead to a decrease in overall performance.  Female endurance athletes in particular are more likely to not meet their protein needs.

Vitamin and mineral intake are also important considerations for endurance athletes.  Micronutrients are essential for optimal metabolic health, as various vitamins and minerals support functions like energy production, muscle growth, and recovery, all of which are central to performance for endurance athletes. 

Carbohydrate Strategies for Energy Maintenance

Carbohydrates are an important macronutrient for endurance performance, as they provide a simple source of fuel for immediate energy production. Additionally, carbohydrate intake has been linked to immune health benefits in endurance athletes, and intake may also improve the bioavailability of other supplements, such as protein supplements, that are needed for athletes to meet their energy demands. While some endurance athletes may strategically train with lower-carbohydrate intake to improve fat oxidation and aerobic capacity, current research still points to carbohydrates as an essential energy source for endurance sports, particularly during higher-intensity training. While protein and fat can still provide energy, carbohydrates are most efficiently metabolized by the body and can be broken down quickly enough to be used intra-exercise by endurance athletes.  

Carbohydrates also help to replenish glycogen stores, with carbohydrate loading strategies primarily aimed at optimizing glycogen supply before an event. Inadequate glycogen reserve has been linked to a negative impact on performance in endurance athletes, especially during periods of strenuous training or competition. Carbohydrate loading strategies typically involve consuming on average 10-12 grams of carbohydrates per kilogram of body weight per day for 36-48 hours before an event, with most athletes also following a “low residue” (low fiber) diet during the loading protocol to minimize gastric distress. Rapidly absorbed, simple carbohydrates such as rice, potatoes, honey, or fruit are typically recommended over whole-grain, high-fiber carbohydrates for loading protocols. Immediately before an event, an additional intake of 1-4 grams of carbohydrates per kilogram of body weight in the 1-2 hours pre-event is often helpful to “top off” glycogen stores after an overnight fast.

Protein’s Role in Muscle Recovery and Adaptation

While protein intake after training is often emphasized for strength training, it’s also important for endurance athletes to consider protein intake as part of an overall nutritional strategy for optimizing performance. Endurance exercise has been found to alter protein metabolism and can lead to hypertrophy of skeletal muscle, making protein intake post-training essential for recovery and adaptation to training. Prolonged endurance training sessions also stimulate the oxidation of amino acids for energy, particularly branched-chain amino acids (BCAAs). For this reason, it can be beneficial for endurance athletes to consume adequate essential amino acids to not only repair exercise-induced muscle damage but also to supply supplemental energy for longer training sessions.  

Nutrition consensus statements from various dietetic associations state that athletes should aim for a protein intake of 1.2-1.4 grams per kilogram of body weight, which is 50-75% higher than the current RDA for the general population of 0.8 grams per kilogram of body weight. However, some studies suggest that a higher protein intake, upwards of 2 grams per kilogram of body weight, may be more beneficial for endurance athletes to maintain protein balance and meet training needs.  

Post-training or event sessions, protein intake accompanied by dietary fiber may be a good strategy to help prolong the availability of amino acids for endurance athletes. Endurance athletes may have a longer post-training window for protein synthesis than found with resistance training, so dividing up protein intake between two meals within a 6-hour window for ongoing protein synthesis may also be ideal. Readily digestible sources of protein with a high leucine content, such as grass-fed whey protein, are ideal for maximizing muscle protein synthesis after a training session. 

The Importance of Fats in Endurance Performance

While carbohydrate intake is often a focal point for endurance athletes, dietary fat intake is important for overall health, including optimal hormone function as well as serving as another energy source. Having fat intake fall to less than 20% of an athlete’s caloric intake can increase their risk for micronutrient deficiency and essential fatty acid deficiency, both of which can take a toll on recovery and performance.  

Endurance athletes can use nutritional strategies alongside training to help improve their metabolic flexibility, or the ability to switch between carbohydrates and fat-burning for energy production. Metabolic flexibility may be particularly beneficial towards the end of longer sessions or races, where glycogen reserves are depleted. “Train low” states involve completing training sessions with a lower-carbohydrate and higher-fat nutritional plan, aiming to improve fat adaptation for endurance athletes in longer, lower-intensity races (such as ultramarathons). However, if an athlete’s focus is on racing and performance time and may involve many “sprint” sessions within the race, a higher-fat and lower-carb diet may impede their ability to train at higher intensities and may not be as beneficial for performance.  

Ultimately, endurance athletes should consider lowering fat intake below 20% of their daily caloric intake only during carbohydrate loading protocols, or pre-race if gastrointestinal discomfort occurs during training from pre-session fat intake. A general intake of 20%-35% is recommended to help preserve overall health. It may be best to consume dietary fats away from training sessions to minimize gastrointestinal distress, having them after training sessions but avoiding pre-session and peri-session fat intake.

Hydration Strategies for Endurance Athletes

For any athlete, the longer the training session is, the more important hydration becomes as the risk increases for dehydration, salt loss, and an overall negative impact on body water balance. Dehydration of just 2-4% has been shown to have negative impacts on athletic performance, with endurance athletes competing in warmer environments more prone to dehydration. However, overhydration and resultant hyponatremia are also a risk for endurance athletes, making it clear that hydration strategies aren’t just about water intake, but also electrolyte and salt balance as well. It should be noted that athletes who often find “white salt stains” on their clothing after training have been observed to have a higher risk of hyponatremia and may need to be strategic about salt intake alongside fluids accordingly.  

No one recommendation can be applied to all athletes due to differences in training load, sweat rate, body mass, and other factors; however, the following recommendations apply to most endurance athletes and can help determine individual fluid intake needs. First, measuring body weight before and after training can help to estimate the amount of water loss experienced during activity, so an athlete can replace fluids accordingly. Second, athletes should pay attention to urine (it should be a pale color) and thirst sensation (it should be low) to ensure hydration is adequate before training.  

The American College of Sports Medicine recommends on average a 400-800 mL/hour fluid consumption rate for athletes and for sodium lost through sweat to be replaced via food or electrolyte supplementation. It’s recommended that athletes “practice” their hydration strategies in training sessions before committing to a plan for race day. For intense prolonged sessions lasting over an hour, fluid intake of 600-1200mL/hour of water that also contains 4-8% carbohydrate alongside 0.5-0.7 grams of sodium per liter can help ensure proper hydration during training.

Micronutrients and Supplement Use

Vitamin and mineral intake are important considerations for endurance athletes, as studies have shown that both men and women competing in endurance sports don’t meet recommended intakes of various micronutrients, including iron, calcium, and magnesium. Micronutrients may help boost mental performance while competing, as well as supporting hormone production and overall cognitive function. Female athletes are less likely to meet their iron intake requirements, and may also have lower levels of other micronutrients important to both overall health and athletic performance, including choline, selenium, zinc, and vitamin B12.

Three specific micronutrients that are especially important for endurance athletes are iron, magnesium, and calcium.  Iron is an important mineral for endurance athletes, as iron deficiency anemia can hurt athletic performance. Athletes are more prone to iron-deficiency anemia than the general population, due to post-training inflammation, sweating, training intensity and muscle repair, and a higher need for nutrient intake in general. While iron supplementation and increasing the frequency of iron-rich foods in the diet is most helpful for athletes who have deficiencies, low-dose iron supplementation even in non-anemic endurance athletes has been shown to help improve training-related stress, mood, and fatigue.

Magnesium benefits endurance athletes due to its impact on blood pressure, heart rate, and VO2 max. Even a slight magnesium deficiency can impact endurance exercise performance and may amplify the oxidative stress that naturally occurs with intense exercise. Additionally, the need for magnesium increases with higher levels of physical exertion, making magnesium needs for endurance athletes higher than that of the general population.  

A third example of a micronutrient important for endurance athletes is calcium.  Calcium is important to optimize bone health in athletes, though is also important for heart function and neuromuscular coordination. Calcium losses may also occur with excessive sweating during longer endurance events, making it an important micronutrient to track and replace as needed.

When it comes to supplementation, it’s best to guide micronutrient supplementation with testing to ensure athletes aren’t over-consuming certain vitamins and minerals. Other supplementations common amongst endurance athletes include caffeine, antioxidants, probiotics, protein supplements, and nitrates (beetroot powder or juice). It’s recommended that endurance athletes work with their coach and practitioners to determine if performance-boosting supplements may play a beneficial role in their training regimen, or if the specific nutrients can be obtained through strategic dietary implementation. 

Nutritional Strategies for Specific Endurance Events

When it comes to nutrition strategies for different types of endurance events, the use of periodized nutrition by athletes and coaches can help personalize a training and recovery program. Periodized nutrition refers to the strategic combination of exercise and nutrition to optimize performance, meaning that nutritional strategies may vary with types of training depending on the goal of each athlete, versus eating the same way constantly. Strategies may vary between types of race events as well.

An example of this concept can be explained by looking at strategies for triathletes. During triathlons, carbohydrates tend to be the primary fuel to ensure easy access to an energy source throughout a fairly long race event. Electrolytes or salt must also be replaced based on the sweat rate of the athletes, in addition to ensuring ongoing fuel intake. While for sprint triathletes, a 24-hour period before the race with a “topping off” of glucogen the morning of the race is likely sufficient to suffice for performance, for longer races, it may take 24-36 hours of carbohydrate loading pre-event followed by strategies carbohydrate intake during the race itself. For race times in the 1-2.5 hour range, consuming 30-60 grams of carbohydrates per hour helps to spare glycogen depletion, while races longer than 2.5 hours may require up to 90g of carbohydrate per hour. Athletes may strategically consume carbohydrates more in the cycle portion of the triathlon, through carbohydrate drinks, gels, or bars, as it tends to be easier to consume while seated on a bike.

Managing Nutrition During Training and Competition

While it can seem daunting to consider all of the different nutritional strategies an endurance athlete can employ to support optimal energy and performance, there are a few basic concepts that are simple to follow that will help to maintain proper nutrition. Prioritizing carbohydrates, fluids, and electrolytes during pre- and peri-training sessions helps minimize the risk of dehydration and ensures an ongoing, accessible fuel source to tap into for athletes. A well-planned hydration strategy that is practiced during training can help make race day much more efficient. Protein intake should also be a focus, with post-workout protein intake particularly important to support muscle recovery and training adaptations. Fat and fiber intake are important for overall health but may be best consumed away from training windows to minimize gastrointestinal discomfort during the race or training session. 

Common Nutritional Challenges and Solutions

Endurance athletes may face a few different nutritional challenges when it comes to optimizing their race-day performance. Common challenges include eating enough calories to meet training demands, as well as consuming enough key nutrients such as protein, calcium, and iron. The timing of food intake can also be challenging, as athletes want to consume food within a timeframe to optimize performance, but also simultaneously minimize gastrointestinal symptoms like bloating, stomach cramps, or needing to have a bowel movement while racing.  

Ongoing injuries, frequent colds, and slow recovery from training may all be signs that an athlete isn’t meeting their nutritional needs and may need to change up their nutritional strategy or supplement based on personalized lab testing. Athletes, especially female athletes, are at a higher risk for RED-S, or Relative Energy Deficiency in Sports, which can be a consequence of continually not meeting caloric needs and having low energy availability. RED-S can lead to poor recovery, poor adaptation to training, hormone imbalances, decreased immunity, and in severe cases compromise of bone health.  

To prevent and address these challenges, endurance athletes can incorporate several things into their training programs. Smart use of supplementation, guided by personalized lab testing, can help address any nutrient gaps identified in their diet alone, especially in athletes who may have dietary restrictions. Additionally, trying out different methods of meal timing and macronutrient intake around training sessions can help athletes identify which feeding schedules work best for their performance and recovery, helping to plan out race day strategies. For example, athletes may want to emphasize carbohydrates and protein closer to their training windows, while reserving fat and fiber intake for post-training meals to ensure they hit their overall dietary needs without compromising feeling their best during a session.  

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Nutritional Strategies for Endurance Athletes: Key Takeaways

When it comes to tailoring nutrition strategies for endurance athletes, it’s not just about eating the right types of foods. Athletes must also consider meal timing pre- and post-training, as well as during training, as many endurance athletes are participating in sessions that can last for multiple hours. A nutrient-dense, balanced diet that covers macro- and micronutrient needs is important for optimal performance, sustained energy, and recovery and training adaptation. Functional medicine lab testing can help identify nutrient gaps in an athlete’s diet that may be preventing them from reaching peak performance, so they can adjust their nutrition and personalized supplementation accordingly.