The Essential Role of Macronutrient Balance in Ultra Running

Long-distance ultra running places extraordinary demands on the body. Races from 50 kilometers to 100 miles and beyond require sustained effort for hours or even days, pushing energy systems to their limits. While training volume and mental toughness are critical, nutrition is the factor that can make or break performance. Properly balancing protein, carbohydrates, and fats is not a one-size-fits-all prescription but a dynamic strategy that must be tailored to the athlete, the race distance, terrain, and climate. Getting this balance right means more even energy levels, reduced muscle breakdown, faster recovery, and a lower risk of gastrointestinal distress. Poorly managed macronutrient intake leads to premature fatigue, bonking, impaired recovery, and increased injury risk.

Understanding the specific roles of each macronutrient and how to manipulate them for training and race day is essential for any serious ultra runner. This guide provides evidence-based recommendations and practical tips to help you optimize your fueling strategy, with expanded insights on individual variability, fat adaptation, and race-day troubleshooting.

Carbohydrates: The Primary Fuel for Endurance Performance

Carbohydrates are the most important fuel source during intense and prolonged exercise. They are stored as glycogen in the liver and muscles, and these stores are limited—typically enough for about two hours of moderate to high-intensity effort. In ultra running, where efforts last many hours, maintaining carbohydrate availability is the single most important nutritional factor for preventing performance decline. The body's ability to store glycogen can be enhanced through proper training and nutrition, but race-day strategies must account for continuous replenishment.

Types of Carbohydrates and Their Timing

Carbohydrates are not all equal. Complex carbohydrates such as whole grains, oats, sweet potatoes, legumes, and brown rice provide a slow, sustained release of glucose. They are ideal for meals in the 24 to 48 hours before a race to top off glycogen stores, a process known as glycogen loading. Simple carbohydrates, found in white rice, potatoes, fruit, and refined pasta, are faster-digesting. These are more appropriate immediately before and during exercise because they minimize the risk of gastrointestinal issues and provide rapid energy. For ultra runners with sensitive guts, choosing lower-fiber sources like white bread, refined grains, or even baby food pouches can reduce bloating and discomfort during the event.

Glycemic Index and Fueling Strategy

The glycemic index (GI) of carbohydrate foods affects how quickly glucose enters the bloodstream. Low-GI foods (like oats, brown rice, lentils) are excellent for pre-race meals because they provide steady energy without rapid insulin spikes. High-GI foods (like sports drinks, gels, white bread) are superior during and immediately after exercise when rapid absorption is needed. A common mistake is consuming high-GI foods hours before a race, leading to an insulin surge that can cause rebound low blood sugar at the start. Practice your pre-race meal schedule during training to see what works for your body.

During-Race Carbohydrate Intake

Research consistently shows that consuming 60 to 90 grams of carbohydrates per hour during endurance exercise lasting more than 2.5 hours can improve performance and delay fatigue. For ultra events lasting 6 to 12 hours, some athletes may require up to 90-120 grams per hour, especially when using multiple transportable carbohydrates (e.g., glucose and fructose mixtures). Sources include energy gels, chews, sports drinks, bananas, and real food like melon or rice cakes. The key is to start fueling early in the race—never wait until you feel hungry or tired. Once you're behind on fuel, it's difficult to catch up. Also consider the form of fuel: liquid calories are often easier to digest than solid food, especially in hot conditions or at high altitude. A mix of both can reduce flavor fatigue.

Training the Gut

Many ultra runners fail to meet their target carbohydrate intake during races because their digestive system isn't trained to handle large volumes of fuel. Gut training involves practicing your race-day nutrition plan during long training runs: start with lower amounts (30–40 g/hour) and gradually increase to your target over several weeks. This improves absorption and reduces the risk of nausea, cramping, or diarrhea on race day. Some athletes find that experimenting with different carbohydrate ratios (e.g., 2:1 glucose to fructose) enhances absorption without gut distress. For more detailed guidance on carbohydrate intake and gut training, refer to the Sports Dietitians Australia endurance nutrition factsheet.

Practical Carbohydrate Recommendations

  • Pre-race (3–4 hours before): 200–300 grams of complex carbs from a low-fiber, low-fat meal.
  • Pre-race snack (30–60 min before): 30–50 grams of simple carbs, such as a banana or an energy gel.
  • During race: aim for 60–90 grams per hour, adjusting for heat, altitude, and gut tolerance.
  • Post-race: consume 1.0–1.2 grams of carbohydrate per kilogram of body weight within 30 minutes, then every two hours for the next 4–6 hours to replenish glycogen stores.

Protein: Repair, Recovery, and Adaptation

While carbohydrates dominate the conversation during an ultra, protein is equally important before and after the event—and even during very long races. During prolonged exercise, muscle protein breakdown increases. Consuming protein during and after exercise helps limit breakdown and stimulates muscle protein synthesis, supporting repair and long-term adaptation. For ultra runners, adequate protein intake also aids immune function and connective tissue health, both of which take a beating during training blocks. Inadequate protein over weeks of high-volume training can lead to persistent soreness, frequent illness, and reduced performance.

Daily Protein Requirements for Ultra Runners

The general recommendation for endurance athletes is 1.2 to 2.0 grams of protein per kilogram of body weight per day. Athletes doing high-volume training or long back-to-back runs may need toward the higher end. For a 70 kg runner, that means 84–140 grams of protein daily. This can be distributed across three to four meals, with an emphasis on eating protein within two hours after the longest or most intense runs. Spreading protein intake across multiple meals maximizes muscle protein synthesis compared to eating a single large dose.

High-Quality Protein Sources

  • Lean meats: chicken, turkey, lean beef
  • Fish: salmon, tuna, mackerel (also good for omega-3 fats)
  • Eggs and dairy: Greek yogurt, cottage cheese, milk
  • Plant-based: tofu, tempeh, edamame, lentils, chickpeas, quinoa
  • Supplements: whey or plant-based protein powders for convenience post-run

Protein Timing for Ultra Events

For ultra races lasting more than 8 hours, some athletes benefit from small amounts of protein during the run to help preserve muscle mass. Research suggests that adding a small amount of protein (e.g., 5–10 grams per hour) to carbohydrate intake might improve performance and reduce muscle damage in very long events. However, too much protein during a race can cause stomach upset. It is wise to practice protein-containing foods (like nut butter, turkey wraps, or sports drinks with protein) during long training runs before attempting them in a race. Post-race, aim for 20–30 grams of high-quality protein combined with carbohydrates to maximize recovery. The post-run window is also a good time to include protein that contains leucine, an amino acid that strongly stimulates muscle protein synthesis. Dairy sources like milk and yogurt are rich in leucine.

For a deeper look at protein needs for endurance athletes, see this review from the Strength and Conditioning Journal.

Fats: The Endurance Fuel That Keeps Going

Fats are the body's most energy-dense macronutrient, providing 9 calories per gram. During ultra running, especially at lower intensities and after glycogen stores begin to deplete, your body increasingly relies on fat oxidation for energy. For events exceeding 4–6 hours, the ability to efficiently burn fat becomes a major performance advantage. This is why dietary fat quality matters for endurance athletes, not just for energy but for absorption of fat-soluble vitamins (A, D, E, K) and hormone production.

Healthy Fat Sources for Ultra Runners

Not all fats are created equal. Focus on unsaturated fats from whole food sources:

  • Nuts and seeds: almonds, walnuts, chia seeds, flaxseeds
  • Avocado and olive oil
  • Fatty fish: salmon, sardines, mackerel (also provide omega-3s for reducing inflammation)
  • Coconut (moderate amounts for MCTs, which can be used for quick energy)
  • Dark chocolate (in moderation for polyphenols)

Fat Adaptation and Metabolic Flexibility

Some ultra runners experiment with "fat adaptation" strategies, where dietary carbohydrate is reduced and fat increased to train the body to burn fat more efficiently. While this can improve metabolic flexibility, research does not support high-fat diets for performance in high-intensity efforts. Most elite ultra runners rely on high carbohydrate availability for race day, and incorporate healthy fats during training to meet energy needs and support overall health. A sensible approach is to consume 20–30% of total daily calories from fats, with a focus on sources that provide essential fatty acids and fat-soluble vitamins. For athletes aiming to improve fat oxidation, a periodized approach works best: maintain higher carbohydrate intake around intense sessions, and allow lower-carb days or extended easy runs to stress the fat-burning pathways. These strategies require careful monitoring to avoid under-fuelling and hormonal disruption.

Fats During the Race

Consuming significant amounts of fat during an ultra is difficult due to slow digestion. However, small amounts of healthy fat from nut butters, coconut flakes, or a handful of trail mix can add calorie density and provide a sustained energy release for very long efforts. Experiment during training to find what your gut tolerates. Some athletes use medium-chain triglycerides (MCT oil) as a rapid fat energy source, but they can cause gastrointestinal distress if not gradually introduced. For further reading on fat metabolism in ultra endurance, see this research summary from the UltraRunning Magazine.

Striking the Right Macro Balance

The ideal macronutrient split varies based on race distance, intensity, individual metabolism, and personal tolerance. The following ranges are general starting points for ultra runners:

  • Carbohydrates: 50–65% of total daily calories
  • Protein: 15–20% of total daily calories
  • Fats: 20–30% of total daily calories

For a 70 kg runner consuming 3,000 calories per day (average during heavy training), that translates to roughly 375–488 grams carbohydrates (50–65%), 112–150 grams protein (15–20%), and 67–100 grams fat (20–30%). However, these numbers should be adjusted based on individual response, training phase, and body composition goals. Athletes with a history of low energy availability (RED-S) may need to prioritize carbohydrates and overall calories.

Race-Specific Adjustments

  • 50K–50 mile races: Higher carbohydrate emphasis (closer to 60–65%) to maintain high intensity. Protein can be slightly lower (15%) because muscle damage is less severe.
  • 100 mile + events: Slightly higher fat intake in the days before (20–25%) to encourage fat adaptation, but carbohydrate remains key during the race. Protein intake during the race may be beneficial for those prone to muscle breakdown.
  • Back-to-back training days: Increase protein slightly (toward 2.0 g/kg) to aid recovery between sessions. Also emphasize high-carb recovery meals within 30 minutes of each workout.
  • Off-days or recovery weeks: Reduce total calories, especially carbohydrates, while maintaining protein and healthy fat intake. This allows the body to rest metabolic systems and improve insulin sensitivity.
  • Hot or high-altitude races: Increase fluid and electrolyte intake, but also consider higher carbohydrate needs due to increased energy expenditure and potential for reduced appetite. Simple, liquid fuels are often better tolerated.

Carbohydrate Periodization

Periodizing carbohydrate intake around training sessions is a strategy used by many elite athletes. Consume higher carbs on heavy training days and lower carbs on easy or rest days to enhance fat adaptation and metabolic flexibility. This approach can improve the body's ability to spare glycogen during races, but requires careful planning to avoid under-fuelling. For example, on a double-run day, front-load carbohydrates before and after the first session, then moderate intake through the rest of the day. On a recovery day, aim for lower total carbs but still include protein at each meal to support repair.

Practical Nutrition Tips for Ultra Runners

  • Test everything in training. Race day is not the time to try new gels, bars, or meal timings. Replicate your nutrition strategy during long runs and tune-ups. Test your full fueling plan at least 3–4 times before the event.
  • Gut training is real. Practice consuming 60–90 grams of carbs per hour during training runs to teach your digestive system to handle fuel without distress. Start with lower volumes and increase gradually over several weeks.
  • Hydrate strategically. Water is not enough; consume electrolytes (sodium, potassium, magnesium) to maintain fluid balance and prevent hyponatremia. Aim for 500–750 mL of fluid per hour, adjusting for sweat rate and heat. Use sports drinks that match your electrolyte needs.
  • Include micronutrients. Ultra running depletes iron, calcium, vitamin D, and B vitamins. Eat a rainbow of vegetables, lean meats, and fortified foods, or consider blood testing every 6 months. Iron deficiency is common in runners, especially women, and can severely impair endurance.
  • Listen to your body. Fatigue, poor concentration, and cravings can signal under-fuelling. Adjust your intake based on how you feel and your training load. Keep a simple log of how you feel during and after runs to identify patterns.
  • Plan for aid stations. Know what will be available on course and have backup fuel. Many runners carry tops of their own comfort foods. Also know where drop bags are allowed and pack them strategically with different fuel options in case you get bored or intolerant of one source.
  • Recovery nutrition beyond the first hour. The post-race window is important, but consistent nutrient timing over the next 24 hours matters just as much. Continue to prioritize protein and carbohydrates at every meal to support full recovery.

Putting It All Together: A Sample Day of Balanced Nutrition

The following example is for a 70 kg runner on a 3-hour long run day with moderate intensity. Adjust portion sizes to your body weight and activity level, and substitute foods based on your preferences and tolerances.

  • Breakfast (2–3 hours before run): Oatmeal (80g oats) with 1 banana and 2 tbsp almond butter + 250 mL milk (~50g carb, 18g protein, 20g fat)
  • During run (per hour): 2 energy gels (25g carbs each) + 500 mL sports drink (30g carbs) = 80g carbs per hour. If running more than 3 hours, add a small amount of protein (e.g., one protein chew per hour) to test tolerance.
  • Post-run (within 30 min): 500 mL chocolate milk (30g carb, 12g protein) + 1 rice cake with peanut butter
  • Lunch: Large grilled chicken wrap (whole wheat tortilla, grilled chicken, avocado, mixed greens, hummus) ~60g carb, 40g protein, 25g fat
  • Snack: Greek yogurt (200g) with berries and a handful of almonds ~30g carb, 20g protein, 15g fat
  • Dinner: Salmon fillet (150g) with sweet potato (200g) and roasted broccoli ~40g carb, 35g protein, 20g fat. Drizzle olive oil for extra healthy fats.
  • Evening snack: Cottage cheese (200g) with pineapple ~15g carb, 25g protein, 5g fat

Total (approximate): 305g carbs, 155g protein, 95g fat, ~2,700 calories. This provides a solid foundation for recovery and supports next day's training. Adjust based on your specific needs—if you feel hungry mid-afternoon, add another snack; if you're trying to lose weight, adjust portion sizes but keep protein high.

For variety, consider different combinations: a quinoa bowl with black beans and avocado for lunch, or a stir-fry with tofu and brown rice for dinner. The key is consistent distribution of protein and carbs across all meals.

Final Thoughts on Personalizing Your Nutrition

There is no single "perfect" ratio of protein, carbohydrates, and fats for every ultra runner. The science of sports nutrition provides excellent guidelines, but individual factors—gut sensitivity, training history, race distance, climate, and personal taste—must drive the final plan. Commit to testing different fueling strategies during training blocks. Keep a nutrition log, note how your body responds, and refine your approach. Over time, you will develop an intuitive understanding of how to fuel for your best performance.

If you struggle with persistent gastrointestinal issues, extreme fatigue, or are recovering from injury, consider working with a registered dietitian certified in sports nutrition. They can help you identify specific adjustments, such as timing of fiber intake, handling of food allergies, or addressing under-fuelling. For comprehensive sports nutrition guidelines, the American College of Sports Medicine (ACSM) offers a joint position statement on Nutrition and Athletic Performance. Consult an expert if you have specific goals or medical conditions—it can save months of trial and error.