Nutrition for Ultra-Marathons: Fueling Ultra Runners

Ultra-marathons, those races exceeding the traditional marathon distance of 26.2 miles (42.2 km), have been gaining popularity over the past few decades. These events challenge athletes to run long distances, often in extreme conditions and remote locations. Training and racing in ultra-marathons require not only physical endurance but also careful attention to nutrition.

Nutrition for Training

Daily Caloric Requirements

Several factors influence your daily caloric needs, including your basal metabolic rate, daily activity level, training requirements, body composition, and the thermic effect of food digestion. For ultra-marathon runners, these needs are also affected by body mass, training status, session duration, environmental conditions, and terrain.

To give you an idea, a 50kg female with 15% body fat who runs for one hour at a moderate pace would require about 2004 calories per day to maintain balance. If she increases her training sessions to three hours at the same pace, her daily requirement would be approximately 2726 calories. On the other hand, running at a faster pace for three hours would necessitate around 3423 calories per day.

Training on challenging terrain and in extreme conditions, like heat or high altitude, significantly increases caloric and carbohydrate requirements.


To maintain energy balance, especially on heavy training days, you might need to consume more calories than usual. It’s essential to consider both training and recovery requirements throughout the week unless you have specific weight goals.

Macronutrient Distribution

For ultra-marathon runners, a typical macronutrient distribution consists of approximately 60% carbohydrates (CHO), 15% protein, and 25% fat to support their endurance training.

When adjusting for body weight, runners engaged in intense training sessions may need between 5-8 grams of carbohydrates per kilogram of body weight per day. Some might even require 7-10 grams per kilogram.

Protein intake is essential for recovery, and athletes should aim for at least 1.6 grams of protein per kilogram of body weight per day. In some cases, up to 2.5 grams per kilogram might be necessary.

Fat intake should range from 1.0-1.5 grams per kilogram per day, but heavier or faster individuals might need closer to 2.0 grams per kilogram to meet their caloric needs.

It’s important to note that these recommendations should be tailored to individual factors, including training duration, pace, and body mass.

Ketogenic Diets

Ketogenic diets, which are very high in fat and extremely low in carbohydrates, have gained attention among endurance athletes. While some early studies showed potential benefits for fat oxidation, there’s not enough evidence to recommend these diets for ultra-marathon training. Ketogenic diets can cause fatigue, gastrointestinal discomfort, and may compromise high-intensity performance.


Proper hydration is crucial for ultra-marathon runners, who can lose significant amounts of fluid during training and races. Dehydration can impair performance and health.

Day-to-Day Fluid Intake

For daily hydration needs, drinking to thirst is generally a suitable strategy. Individual fluid requirements can vary, but your body’s thirst sensation is a reliable indicator of when to drink.

Post-Exercise Fluid Intake

After training, it’s essential to replenish fluid losses. Simply drinking to thirst may not be enough at this time, so consider consuming a volume greater than what you’ve lost. Including sodium in your post-exercise drink can enhance hydration.

Hydration Monitoring Strategies

Simple tools like urine color charts can help you estimate your hydration status. Monitoring your hydration is essential for your overall health and performance.

Nutrition For Racing

The considerations for racing in ultra-marathons, including energy and macronutrient demands, energy expenditure, energy intake, carbohydrate versus fat intake, protein intake, and strategies to offset dehydration, are all critical factors to ensure optimal performance and overall health during these demanding races.

nutrition for running ultras

Energy and Macronutrient Demands:

Ultra-marathons involve prolonged and strenuous efforts, leading to substantial energy expenditure. Athletes should aim to minimize caloric deficits before and after the race.

Carbohydrate (CHO) availability is crucial for racing. A contemporary CHO-loading strategy (around 10 g/kg/day) in the 48 hours leading up to the race can help maximize CHO stores.

Pre-race meals should be rich in carbohydrates and easily digestible while avoiding high-fat and high-fiber foods to prevent gut discomfort during the race.

Energy Intake:

Successful completion of ultra-marathons is associated with greater energy and fluid intake. Runners should aim to consume calories during the race to mitigate calorie deficits. Recommended caloric intake during the race varies with distance: approximately 150–300 Kcal/h for races up to 50 miles and 200–400 Kcal/h for longer races.

Persistent calorie intakes below 200 Kcal/h are not recommended. Runners should persevere with feeding even when experiencing nausea, especially in the later stages of the race, to avoid hypoglycemia.

Carbohydrate vs. Fat Intake:

While fat oxidation rates are higher in ultra-marathons compared to shorter races, maintaining an adequate intake of carbohydrates is crucial to prevent early-onset fatigue. Individual strategies for carbohydrate and fat intake vary, but successful runners may require a higher tolerance for both.

High carbohydrate intake rates (up to 90 g/h) may be unrealistic for longer ultra-marathons and can lead to GI distress.

Protein Intake:

Protein intake during racing is often overlooked but may help mitigate muscle damage and positively influence energy metabolism.Finishers in ultra-marathons tend to have higher protein intake compared to non-finishers.

Runners should strive to consume 20–30 g of protein every 3 hours during the race, balancing it with carbohydrates and fats.

Offsetting Dehydration:

Dehydration can have negative effects on performance and health, particularly in hot and humid conditions. Drinking to thirst is a suitable strategy for shorter and cooler races, but for ultra-marathons, individualized hydration plans based on sweat rates should be determined in advance.

Runners should aim to consume 150–250 mL of fluid approximately every 20 minutes during the race.

Exercise-Associated Hyponatremia (EAH):

EAH is a dangerous condition caused by excessive fluid intake without adequate sodium replacement. Runners should aim to consume sodium in concentrations of 500–700 mg/L of fluid, with higher amounts required in hot and humid conditions. Runners should avoid overhydration, as this will cause dilution of blood sodium.

It’s important for ultra-marathon runners to tailor their nutrition and hydration strategies based on individual preferences, body size, race conditions, and prior experiences. Regular training and experimentation with different foods and fluids can help athletes fine-tune their race-day nutrition plans to optimize performance and minimize the risk of adverse events like dehydration and EAH. Additionally, seeking guidance from a specialized sports dietitian is advisable to develop personalized nutrition strategies.

GI Distress in Ultra-Marathon Running:

GI distress is a common issue among ultra-marathon runners, affecting a significant percentage of athletes, with nausea being a prevalent symptom.

The exact causes of GI distress during ultra-marathon races are multifactorial, but it is often related to reduced blood flow to the GI tract, dehydration, and increased core temperature. These factors can compromise gastric emptying and intestinal transport.

Increased systemic lipopolysaccharides (LPS) from gut bacteria due to intestinal tight-junction disruption can lead to immune responses and GI distress.

Strategies to minimize GI distress include avoiding highly concentrated carbohydrate (CHO) solutions, limiting saturated fat intake, avoiding non-steroidal anti-inflammatory drugs (NSAIDs), and maintaining hydration.

The use of “multiple transportable carbohydrate” solutions (containing glucose, fructose, and/or maltodextrin) can help improve carbohydrate absorption and reduce GI discomfort.

Training the gut and individualized nutritional strategies may help reduce the impact of GI symptoms during races. Low FODMAP diets may benefit those with irritable bowel syndrome (IBS).

Probiotic supplements, particularly Lactobacillus and Bifidobacterium species, may help modify GI microbiota and reduce GI symptoms. However, further research is needed. The inclusion of dietary prebiotic nutrients may support GI epithelial integrity.

Supplements and Medications:

Caffeine is commonly used by ultra-marathon runners due to its stimulant properties. It can enhance endurance performance and cognitive function but should be used carefully to avoid side effects.

The dose and timing of caffeine intake can vary based on individual sensitivity and race duration.

Medium-chain triglycerides (MCTs) and ketone esters have been studied as potential supplements to enhance fat metabolism, but their ergogenic effects in ultra-marathon running are inconclusive.

Vitamins and mineral supplementation do not show significant benefits for ultra-marathon performance unless there is a pre-existing deficiency.

Vitamin C may help reduce oxidative stress and the risk of upper-respiratory-tract infection, but more research is needed.

L-glutamine may support GI epithelial integrity, but further research is needed in the context of ultra-marathon running.

The use of NSAIDs (non-steroidal anti-inflammatory drugs) during ultra-marathons is discouraged due to potential adverse effects and contraindications. Other non-NSAID analgesics (e.g., paracetamol) should be used cautiously to avoid masking pain symptoms that could indicate injury.

Athletes should be cautious about supplement contamination with banned substances when competing in events overseen by anti-doping organizations.

by Manuel Attard M.Sc RD – Sports Dietitian & Nutritionist in Gozo, Malta

Published by Manuel Attard

Manuel Attard Registered Dietitian & Nutritionist

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