[Research Rundown] The Key to Better Marathon Times? Fueling!

Running a marathon is not just a test of your legs and lungs – it's a test of your fueling and hydration strategy. If you’ve ever hit the dreaded “wall” at mile 20 or felt like a dried-out sponge by the finish, you’re not alone. A growing body of research (and plenty of real-life bonking stories) shows that what and how much you eat and drink during a marathon is absolutely critical for performance. Yet, many runners – especially recreational and intermediate marathoners – are undercutting their potential by under-fueling and under-hydrating. 

In fact, meeting the carb guideline was significantly associated with a higher probability of a sub-3:00 finish. In plain terms: the better-fueled runners tended to run faster.

In this edition of Research Roundup, we dive into a brand-new study that confirms most marathoners aren’t taking in enough carbs or fluids on race day, and explore why getting your fueling right is so important (with a few coaching anecdotes, a dash of humor, and practical tips along the way).

New Study: Most Marathoners Are Running on Empty (Literally)

A recent research article  titled “Nutritional Intake and Timing of Marathon Runners: Influence of Athlete’s Characteristics and Fueling Practices on Finishing Time” looked at how runners actually fuel themselves in races – and the results were eye-opening. In this study, 160 runners in the 2022 Seville Marathon provided details on what they ate and drank during the race. The majority of these runners were just doing their own thing (no formal nutrition plan or coaching), which is pretty common. The researchers then compared their self-chosen fueling to expert recommendations and looked at finish times.

First marathon, 1 gel.

Here are the key findings, in plain English:

• Most marathoners weren’t even close to the recommended carb intake. On average, runners consumed only about 35 grams of carbohydrate per hour during the marathon. For reference, that’s roughly the amount in a single gel or a small sports drink bottle. Sports nutrition guidelines for endurance events suggest at least ~60 grams of carbs per hour (and up to 90 grams/hour) for races longer than 2.5 hours. In other words, these runners were barely getting half of the carbs they likely needed.

  
  

• Sodium (electrolyte) intake was also far below recommendations. Runners took in around 192 mg of sodium per hour on average, mostly from sports drinks or the occasional salt packet. Experts recommend about 300–600 mg of sodium per hour for long races to replace what you sweat out. So again, most runners were short on salt. (No, this doesn’t mean start chugging soy sauce – but a sports drink or electrolyte mix can do wonders.)

  
  

• Fluid intake was just barely adequate. The marathoners drank roughly 466 mL of fluid per hour (that’s about 16 ounces, or one typical water bottle). This is actually at the lower end of what’s recommended – guidelines suggest aiming for ~400–800 mL of fluid per hour depending on your sweat rate and the weather (although some runners need much more than that!) So if you’re a heavy sweater or it’s a hot day, 16oz/hour might not cut it. And remember, this is an average; I can guarantee you, many runners drank less than that, or not at all (yes, I've seen some people brag about not even drinking water during a marathon. Just... why?) while a few might have overdone plain water without enough salt (a recipe for hyponatremia). But on average, fluid intake was just about the bare minimum.

  
  

• Those who did fuel properly performed better. Here’s the kicker: the runners in the study who managed to consume around 60–90 g of carbs per hour (hitting the recommended range) were far more likely to finish under 3 hours than those who didn’t. In fact, meeting the carb guideline was significantly associated with a higher probability of a sub-3:00 finish. In plain terms: the better-fueled runners tended to run faster. Meanwhile, the under-fueled folks were disproportionately among the slower finishers (worse performance). Correlation isn’t causation, but this strongly suggests that inadequate fueling was one factor holding many runners back.

  
  

• Lack of knowledge was a major factor. Why were these runners so far off the nutrition marks? The study found that most of the athletes had never received nutrition counseling from a sports dietitian.They were essentially winging it with their “self-selected” race nutrition. Not surprisingly, without guidance, they failed to meet the established carb, fluid, and sodium recommendations in most cases. This points to a big knowledge gap – many runners simply don’t know how much they should be eating/drinking in a marathon, or how to effectively do it.

3rd marathon, 7 gels

This new research confirms a pattern coaches have observed for years: marathoners, left to their own devices, often under-fuel and under-hydrate, and it likely hurts their performance. If you’ve been the runner guzzling a cup of water here and nibbling a half gel there, thinking it’s enough, the science says otherwise. And you’re not alone!

Now, TRUST ME WHEN I SAY: I have been there too! My first marathon, I took 1 gel. My second marathon, I took zero gels (and ran about 15 minutes slower than my first one!). I understand what it's like to not realize how important it is, or to think it's optional, or to think that NOT fueling is a better choice. It's OK!

But now you know! Fueling for your marathon (and half marathons, and training runs!) is as essentially to your race day performance as your long runs and race pace work.

5 Reasons Runners Fail to Fuel/Hydrate Properly (and How to Fix It)

If proper fueling and hydration are so crucial, why do so many of us get it wrong? As a coach, I hear a lot of reasons (and let’s be honest, excuses) for skipped gel packets and scanty sipping. Here are the five most common issues that trip runners up, plus some anecdotes and tips so you can avoid these pitfalls:

Ignorance of the Guidelines. 

Simply put, many runners don’t know how much they should be eating/drinking in a marathon. If no one ever taught you the 60–90 g/hour carb rule or the 16–27 oz/hour fluid guideline, you might assume a couple gulps of Gatorade and one gel for the whole race is fine. I once coached a first-time marathoner who thought taking one gel at mile 20 was “probably overkill” – oops! After educating him on proper mid-race fueling (we aimed for ~40–50g carbs/hour in training to build up from zero), he finally had the energy to push through the finish without hitting the wall. The new study echoed this knowledge gap: most runners hadn’t consulted a dietitian and failed to meet recommendations as a result.

The fix: Educate yourself (you’re doing it now, high-five!). Learn the evidence-based guidelines and make a fueling plan before race day. If you’re unsure, consider talking to a sports dietitian or coach who can provide personalized targets.

Misunderstanding the Recommendations for Marathon Fueling

Even when runners do know the guidelines, they can be confusing. Misinterpretation is common. For example, “60–90 grams of carbs per hour” – what does that actually look like in gels, chews, or sports drink? It’s easy to get the math wrong. One athlete I worked with told me she drank a sports drink at every aid station, thinking she was nailing her carbs – but she didn’t realize each cup was only ~6 grams of carb when we did the math! Some runners also think if they carb-loaded before the race, they don’t need much during, which is a mistake (even the best carb-loading only delays the need for intake, it doesn’t replace it). And let’s not forget pacing: grabbing two gels at mile 24 won’t save you if you’ve been running on empty since mile 15.

The fix: Translate the recommendations into a concrete plan. For example: “I will take one gel (25g) every 30 minutes and drink 500 mL of sports drink (15g) per hour.” That would give ~60-65g of carb/hour – right in range. Also, practice in training to fine-tune what products and timing work for you. If something isn’t clear (like how much sodium is in my drink, or how many ounces my handheld bottle holds), find out well before race day. Think of it like learning the choreography before a dance – don’t wing it on stage! Need specific help? Talk to a sports RD!

Fear of Sugar and Carbs. 

In today’s diet culture, sugar is a four-letter word. I spent too many years thinking that I was hacking my body through "fat adaptation" and cutting out all carbs. Surprise: I got WAY faster once I started eating carbs again! Many health-conscious runners are afraid that taking gels or sport drinks somehow goes against eating “clean” or will cause an energy crash. I’ve heard runners say they avoided Gatorade at aid stations because “I don’t drink soda” or they stick to water and maybe a banana because gels are seen as expensive, glorified candy. Others fall for the allure of low-carb diets – thinking they’ll become ultra-efficient fat-burners and won’t need carbs to race. Unfortunately, these notions are counterproductive for endurance performance. During a marathon, carbohydrates are your friend! It’s high-octane fuel for your muscles and brain. As sports nutritionist Louise Burke famously noted, carb-loading and high-carb intake can significantly improve performance, whereas chronic low-carb intake can hurt it.

The fix: Reframe carbs as a performance fuel, not a junk food. Marathon day is not the time to count sugar grams or stick to kale smoothies – you can go back to your green juice tomorrow. If you’re worried about GI upset from sugary gels, start with lower amounts and train your gut to handle more (your intestines adapt over time to absorb carbs if you practice).

Remember, the motto for racing is “fuel the work” – you will burn those carbs for a purpose. And if you’ve been low-carbing, consider gradually reintroducing carbs in training to see the difference in energy levels. Your permission slip: during endurance exercise, sugar is a-OK and very necessary.

Fear of Weight Gain (or Water Weight)

This is a big one, especially for runners who are watching their weight. It sounds counterintuitive – why would anyone worry about weight gain during a race? – but I’ve had clients intentionally under-fuel because they didn’t want to “drink too many calories” or they avoided carb-loading because they saw the scale go up a couple pounds. Yes, aggressive carb-loading can make you gain ~2-4 pounds temporarily, because for every gram of stored glycogen, your body stores about 3 grams of water. Some runners panic at this normal water-weight gain. fearing it’s “fat” or that they’ll carry extra weight on race day. The result? They don’t fuel fully, start the race with suboptimal glycogen, and then run out of energy – a far worse outcome than lugging an extra pound of water. Similarly, not drinking during a race in hopes of weighing less at the finish is a misguided strategy – the performance cost of dehydration far outweighs any theoretical time gained by being a pound lighter. (In fact, dehydration slows you down, so you finish later – so much for that plan!)

The fix: Recognize that any minimal weight changes from proper fueling/hydration are either water or the weight of fuel that is actively powering your run. That 2-pound gain from carb-loading? It’s mostly water that will keep you hydrated, and fuel that will be burned for energy. You’ll likely pee out or sweat out the extra fluid, and burn off the extra glycogen during the race. It’s not fat. Think of fuel and hydration as part of your race equipment – like a built-in aid station. Would you rather be 2 lbs lighter but running on empty, or properly fueled and finish stronger? I promise you, the PR you might set by fueling properly will feel a lot better than seeing a slightly lower number on the scale. Trust the process: eat to compete, and save weight management for another day, like when you're not training for a race!

Perceived Inconvenience (AKA “It’s a hassle”). 

Let’s face it: fueling during running isn’t the most convenient thing. You have to carry gels or wear a hydration pack/belt, slow down to gulp from a cup without spilling all over your face, and deal with sticky fingers or wrappers. Some runners simply don’t bother because it’s a pain. “I don’t want to carry a bottle for 26 miles,” “Gels are too messy,” or “I’ll just rely on the aid stations” are common sentiments. Even experienced athletes can fall into this trap during training – I’ve had days where I debated what to bring, even though I know better. A sports scientist, Andy Blow, put it well: on a bike you can stash bottles and gels easily, but on a run it takes more effort, so runners often skip fueling out of sheer laziness or discomfort. The result, of course, is subpar performance or bonking.

The fix: Find a fueling method that is least annoying for you, and practice it until it’s second nature. Hate carrying a bottle? Plan routes with water fountains or stash bottles along the way. Don’t like gels? Try chews, sports drinks, or even real-food alternatives that agree with your stomach. There are also handheld bottles, belts, and vest options – lots of gear to make fueling on the run easier. Practice drinking from paper cups on the run (pro tip: pinch the cup to pour into your mouth – fewer spills!). Yes, it’s a bit of extra work, but so is doing long runs in the first place. Think of it as part of your training. It’s far better to deal with a mild inconvenience than to deal with the very inconvenient experience of bonking or crawling the last 10K because you didn’t take in enough fuel or fluid. As one of my marathoner friends likes to say, “Pay the inconvenience tax upfront, or pay the bonk tax later.”

Plan, Practice, and Fuel Like it Matters – Because It Does

If there’s one takeaway from all this, it’s that fueling and hydration are not optional extras for marathoners – they’re fundamental to your success. The new research we highlighted drives home a simple fact: lots of runners could run faster and feel better if they paid as much attention to fueling as they do to pacing or footwear. The reasons for under-fueling range from not knowing what to do, to fearing what might happen, to just not wanting to deal with it. But here’s the good news: you can fix all of these. Educate yourself on the guidelines, put together a nutrition plan for your next race (write it down, even!), and practice that plan during training until your gut and routine are comfortable. Work through any fears by testing things out – you’ll likely find that more carbs and a bit of extra water weight actually make you feel stronger, not sluggish. And embrace the slight hassle of carrying fuel, because the reward at the finish line – whether it’s a PR, not hitting the wall, or simply feeling proud of how you executed your race – is 100% worth it.

Remember, no one ever crosses the finish line of a marathon thinking, “Dang, I wish I hadn’t felt so strong and well-fueled.” More often, it’s the opposite. Don’t let under-fueling or dehydration be the reason you fall short of your goals. As the science and stories show, fueling and hydration are the secret weapons of endurance performance. Stock your arsenal well, and you’ll be ready to battle that marathon with all cylinders firing. Now go forth, practice your fueling, drink up, and make your next marathon your best-fueled one yet – your future self (and your finish-line photos) will thank you!

Sources

American College of Sports Medicine, Sawka MN, Burke LM, et al. American College of Sports Medicine position stand. Exercise and fluid replacement. Med Sci Sports Exerc. 2007;39(2):377-390. doi:10.1249/mss.0b013e31802ca597

Burke LM. Nutrition strategies for the marathon : fuel for training and racing. Sports Med. 2007;37(4-5):344-347. doi:10.2165/00007256-200737040-00018

Fraioli M. Are runners worse at fueling than cyclists and triathletes? Precisionhydration.com. Published October 16, 2023. Accessed May 9, 2025. https://www.precisionhydration.com/performance-advice/nutrition/are-runners-worse-at-fueling-training-and-races-than-cyclists-and-triathletes/

Hansen EA, Emanuelsen A, Gertsen RM, Sørensen S SR. Improved marathon performance by in-race nutritional strategy intervention. Int J Sport Nutr Exerc Metab. 2014;24(6):645-655. doi:10.1123/ijsnem.2013-0130

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Jiménez-Alfageme R, Garrone FP, Rodriguez-Sanchez N, et al. Nutritional Intake and Timing of Marathon Runners: Influence of Athlete's Characteristics and Fueling Practices on Finishing Time. Sports Med Open. 2025;11(1):26. Published 2025 Mar 16. doi:10.1186/s40798-024-00801-w