Most Ultrarunners Aren't Eating Enough

The biggest nutritional challenge facing ultrarunners is not carbohydrates, supplements, hydration, or meal timing. It's eating enough.

In this episode, CTS Coaching Director Cliff Pittman breaks down the International Society of Sports Nutrition's position on ultrarunning nutrition, one of the largest reviews of ultrarunning nutrition ever published.

We discuss caloric intake, carbohydrate recommendations, ketogenic diets, train-low strategies, gut training, hydration, and the practical takeaways athletes can apply immediately to improve performance and recovery.

The message from nearly 200 studies is surprisingly simple: get the fundamentals right before chasing advanced nutrition strategies.

HOST

Cliff Pittman is the Coaching Development Director at CTS, leading the Ultrarunning and Cycling Coaching staff with a specialty in guiding athletes from first-time ultrarunners to elite competitors at races like Western States 100, Leadville 100, and the Triple Crown of 200s. A competitive trail and ultra athlete himself, Cliff brings firsthand experience and a rare ability to turn complex training science into simple, actionable coaching.

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Transcript

Why Ultrarunners Miss The Basics

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The biggest nutritional challenge for ultrarunners isn't macros, timing, or supplements. It's simply eating enough. And that's not my opinion, that's the conclusion of the International Society of Sports Nutrition in one of the most comprehensive reviews of ultrarunning nutrition ever published. Over 25 researchers, nearly 200 studies, and one consensus. Today, we're translating what that research actually says into practical guidance for the everyday athlete. I'm Cliff Pittman, pro ultrarunning coach and director of coaching at CTS. I coach athletes from first-time ultrarunners to professional and world-class competitors. Now, before we get into the specifics, a quick word on why this matters. Ultrarunners get a lot of nutrition advice from other athletes, from social media, from podcasts. The ISSN position stand cuts through all of that noise. It's not one person's opinion or one study's finding. It's the consensus of the research and is worth paying attention to. All right, let's get right into

Calories Are The Real Challenge

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it. Number one, eating enough is your primary challenge. The ISSN identifies matching daily caloric demands as the foremost nutritional challenge facing ultra-marathon runners. Not which macros to prioritize and not what to eat around workouts, not which supplements to take. Calories. And here's why it's harder than it sounds. On big training days, caloric requirements can double or even triple compared to an easy day. A three-hour run creates a fundamentally different energy demand than a one-hour run, and most athletes chronically undereat on their hardest training days. So here's the practical guidance. On training days over three hours, minimize your caloric deficit during the session itself. We'll talk about gut training in a moment, but aim for approximately 20 grams of protein every three waking hours on big training days and increase your meal portions on long run days. Don't eat the same way you would on a rest day when you've just run for four or maybe five hours. And if you still fall short on a big day, make it up on your next rest or recovery day. The simple rule: don't scamp on calories when training demands are high. Everything else in your nutrition plan depends on meeting this baseline first. Alright,

Carbs Stay The Primary Fuel

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number two, carbohydrates are still king. Despite the popularity of low-carb and ketogenic approaches in endurance sports, the ISSN recommends a diet of approximately 60% carbohydrate, 15% protein, and 25% fat for ultrarunners. This recommendation stands even in a sport where fat oxidation matters and races last many hours. On high-intensity training days, the carbohydrate percentage can shift up slightly. On easy or recovery days, it can come down slightly. But carbohydrate remains the primary fuel source across the training week. Now, let's talk about ketogenic diets directly because the evidence here is clear and I'm not going to soften it. The ISSN acknowledges a degree of benefit from ketogenic approaches. Then it documents the downsides fatigue, headaches, poor concentration, lethargy, GI discomfort, nausea, weight loss. If you read that fast enough, it sounds like a prescription drug disclaimer. And just like those disclaimers, the side effects probably aren't worth it. Athletes who are not fully keto-adapted or are still training are doing so in a chronically glycogen-depleted state. So all breakdown, no building back up. That's not a performance strategy. That's a recovery problem. And high fat intake is also associated with poor intake of fiber and key micronutrients such as iron and magnesium, potassium, folate, and antioxidants, all of which are essential for health and performance. Ketogenic diets are a poor fit for athletes trying to train hard, recover well, and perform in long events. The research is very consistent on this. Carbohydrates is your primary fuel. Keep it there. The ones that are not doing this are outliers.

When Train Low Actually Helps

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Number three, train low has limited utility and should be used very carefully. The ISSN acknowledges that training with reduced carbohydrate availability, what's often called training low, can improve fat oxidation. And that's very true. But here's the important context that often gets left out of this conversation. Fat oxidation improves naturally with training volume and easy running. Your body gets better at using fat as fuel when you run a lot of easy efforts without any deliberate manipulation of carbohydrate availability. Train low strategies are a tool, but not a default approach. And for most athletes, the priority should be fueling enough to perform and recover, not engineering a metabolic shift at the expense of training quality. If you do want to incorporate train low, here's what has the most practical utility. Fasted morning endurance runs can be acceptable for easy efforts under two and a half hours at low to moderate intensity. If you are doing intervals or any high quality work, eat beforehand. But do not compromise a quality session in the name of a metabolic adaptation. Two-a-day training to promote fat oxidation is logistically complicated and prioritizes a metabolic shift over training quality and volume. For most athletes, there are more important things to chase, such as staying healthy, building volume, and executing quality sessions consistently. The bottom line on train low. Use it selectively on easy sessions, if ever at all, but never at the expense of the fueling that supports your hard work. Number

Gut Training For Race Day Fueling

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four is train your gut. This is one of the most underappreciated and most actionable areas of ultra-running nutrition. The amount of food and fluid your gut can process during exercise is trainable. Just like your legs adapt to more mileage, your gut adapts to more fuel. If you practice it consistently. Research from Costa, Cox, and Jukendroop shows that fueling at rates above your expected race intake and training builds GI tolerance and reduces distress on race day. So here's the practical application. On long runs, over three hours, fuel at a rate 10 to 30% above your race target. So if you plan to take in 60 grams of carbohydrate per hour on race day, practice at 70 to 80 grams per hour in training. A good general target for gut training is 90 grams of carbohydrates per hour using multiple carbohydrate sources, glucose and fructose combined, which is what most gels, chews, and spork strinks provide when used together. Again, that range is 60 to 90 grams of carbohydrates per hour. So don't save your fueling strategy for race day. Your gut doesn't get a free pass just because there's a race bib on. If you consume 200 calories per hour in training, expect your gut to handle 300 on race day. That's not really a plan. That's a gamble. And ultra rang will collect on it. So practice fueling every long run and do it consistently.

Simple Hydration Checks That Work

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Number five is daily hydration and keep it simple. Monitoring your daily hydration status doesn't require expensive tools or complicated protocols. A widely used framework in sports science called W U T for weight, urine, and thirst gives you a simple daily check-in that requires nothing more than paying attention. On waking, assess three things. Is your weight down from the day before? Is your urine dark? And are you thirsty? If two or more of these are present, you are likely dehydrated going into the day and address it before training. Post-exercise rehydration should replace approximately 150% of fluid loss. So weigh yourself before and after long sessions to calculate how much you lost. And your post-run fluid or meal should contain sodium, either from a drink with an electrolytes, or from food that you eat afterward. Sodium is what allows the fluid you take in to actually be retained and used. So simple, repeatable, and available to every athlete with the scale and some basic awareness.

The Big Takeaways And What’s Next

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So here's the simple message. Ultra running nutrition gets overcomplicated because there is so much noise in this space. Athletes favor the advice of other athletes over actual research and often land on extreme approaches. And that gap between what the science says and what athletes actually do is where performance is lost. The research is very clear on this. Eat enough, especially on hard training days. Keep carbohydrate as your primary fuel and use train low selectively and never at the expense of quality. Train your gut the same way that you train your legs, monitor hydration daily with a simple framework, major in the basics, minor in the marginal gains. That's it. If you want to understand how fueling failures become the primary reason ultrarunners do not finish, my video on the number one reason ultrarunners DNF connects directly to everything we've covered today. Watch that next. And if you want coaching that integrates nutrition into a deliberate, individualized training plan, visit trainwrite.com to connect with the CTS coach and subscribe for more coach driven ultrarunning education.