PF&H Sports Scientist, Chris Harris, highlights five common marathon nutrition mistakes and explains how you can avoid them on race day...
"}},"slug":"how-to-avoid-5-common-marathon-fueling-mistakes","blogTags":"Nutrition","featuredPost":false,"author":{"name":"Chris 'Minty' Harris","slug":"chris-harris","facebookHandle":null,"twitterHandle":null,"instagramHandle":"https://www.instagram.com/harriss_chriss/","linkedInProfile":"https://www.linkedin.com/in/chris-harris-31b915130/","stravaProfile":"https://www.strava.com/athletes/7986372","bio":{"childMarkdownRemark":{"html":"Chris obtained a first-class honours degree in Sport and Exercise Science before passing his MSc in Sport and Exercise Physiology at Cardiff Metropolitan University with distinction.
\nA competitive triathlete and marathon runner himself, Chris has formerly worked as an Exercise Physiologist for sports’ National Governing Bodies and the NHS. As a Sports Scientist at PF&H, Chris provides in-depth evidence-based advice to elite and amateur athletes to help them nail their nutrition strategies for endurance sports.
\nAway from work, Chris ran a 2:40 debut marathon and has competed at both the IRONMAN® and IRONMAN 70.3® World Championships.
"}},"title":"Sports Scientist","headshot":{"file":{"url":"//images.ctfassets.net/428xzyjdw7rf/4S5w7kTEfuVWFoPqNIMtno/8a7a89f7df526b38a90a05d7933dcb86/Minty.webp"}}},"scientificallyReviewed":null,"image":{"resize":{"src":"//images.ctfassets.net/428xzyjdw7rf/3fcIykJ5pMCYH2qPet5XC2/4f436253676b548157acd366b5fb9ca0/resized-PFHxCIM_RaceDay_California_Dec24-1241-ezgif.com-resize.webp?w=1200&h=630&q=70&fit=fill","width":1200,"height":630}},"socialMediaImage":null,"body":{"childMarkdownRemark":{"excerpt":"Even the best laid marathon nutrition plans can go awry with costly mistakes on race day. Some errors might seem minor at first, but can later snowball into…","html":"Even the best laid marathon nutrition plans can go awry with costly mistakes on race day. Some errors might seem minor at first, but can later snowball into significant performance-limiting issues over the course of 26.2 miles.
\nTo help you avoid hitting ‘the wall’ or ending up in the portaloo too often during your next marathon, I’ve taken a look at how you can overcome some common (and potentially race-ruining) fueling mistakes…
\nI see many runners nail their long runs in training without fueling at all, assuming they’ll just take some gels to boost their performance on race day. Others might practice taking carbs in training, but never at race pace, which doesn’t adequately prepare the gut for digesting fuel under race conditions.
\nTraining your gut isn’t just about tolerating carbohydrates. Drinking while running is a skill in itself. Taking fuel without any fluids could also be a recipe for stomach upset, bloating, and poor carb absorption on race day.
\nCase Study: Lucy Reid’s Tough Lesson
\nDuring her debut marathon in Malaga at the end of 2024, Lucy found this out the hard way. She had no issues taking gels in training, but had never practiced drinking at race pace. After a few drinks stations on race day, she began to feel bloated and each sip was causing nausea, which made it harder to fuel effectively.
\nCase Study: How CJ Albertson Trains His Gut
\nCJ Albertson built up his tolerance to carbs over time, and now incorporates fueling and hydration into both long runs and speed sessions, regularly taking in 90-100g per hour.
\nTo practice bottle pickups, he loops past his car every few miles, mimicking marathon conditions. This trains his stomach to handle high-carb intakes at race intensity, which paid off as he successfully averaged ~100g per hour when finishing runner-up at the 2024 California International Marathon with no GI discomfort.
\nHow to train your gut: A structured gut training plan should begin 8-10 weeks before race day, gradually increasing your hourly carbohydrate and fluid intake to reach your race-day targets. The last few long runs should essentially be race simulations of your entire nutrition strategy.
\nRecommended reading: How to train your gut to consume more carb
\nCarb-loading before races is a great strategy to use, but this alone won’t carry you through your entire marathon. Your glycogen stores will deplete during high intensity exercise that lasts longer than 90-120 minutes, so you’ll need some extra energy mid-race to maintain your marathon pace (i.e. by eating gels, chews, bars, real good, or drinking a carb drink). If you wait until you’re hungry before taking anything, it’s too late. This is when energy levels nosedive, your legs feel like bricks and your goal pace will disappear up the road.
\nWhen Kelvin Kiptum shattered the marathon world record with his time of 2:00:35 in 2023, he actually sped up in the final 10km, running his fastest 5km split between 30-35km. This wouldn't have been possible without aggressive fueling throughout the race, ensuring his glycogen levels never crashed, and he could attack the final miles rather than survive them.
\nA Nike Sports Research Lab study modelled the predicted requirements to run a sub-2 hour marathon for both males and females. Their results recommended that males would need to consume ~93g per hour on average, and females even more at ~108g/h to complete the feat. Why did the study report that women needed more exogenous carbohydrates I hear you ask? Mainly because on average, women have less muscle mass than their male counterparts which means they start with less glycogen both in their muscles and liver. Even if you’re not gunning for a world record, the lesson holds: fueling early and often is non-negotiable.
\nHow to avoid ‘the wall’: Start fueling early. Take your first gel, chew, or carb drink within the first 30 minutes of starting the race. Keep fueling consistently so you don’t reach the point of no return.
\nRecommended reading: What happens when you bonk?
\nHydration is just as crucial as fueling. Even mild dehydration can increase heart rate, core temperature, and perceived effort, making race pace feel harder. As fluid levels drop, the body redirects blood flow away from the digestive system, which can lead to stomach distress (this issue is often mistakenly attributed to a fueling issue, when dehydration is actually the cause).
\nWe’ve worked with athletes who complain of suffering with GI discomfort and muscle cramps towards the end of their marathons. Whilst there are several possible causes of both GI discomfort and cramps, it’s possible that dehydration plays some role in both of these marathon-ruining issues.
\nOn the flip side, drinking too much fluid, especially without electrolytes, can dilute blood sodium levels, leading to a condition called hyponatremia. Symptoms range from bloating and nausea to confusion and, in severe cases, collapse.
\nRunners who follow rigid hydration schedules by drinking a set amount per hour without considering their sweat rate or thirst response are at greater risk. Slower runners, who spend more time on the course (and therefore have more opportunities to drink at aid stations) are also vulnerable.
\nTo prevent overhydration:
\nBoth underhydration and overhydration can lead to performance declines. Balancing intake based on individual sweat rates and sweat sodium concentrations is key to avoiding both extremes.
\nHow to optimise your fluid and sodium intake:
\nRecommended reading: Why sodium is crucial to athletes performing at their best
\nElite marathoners usually have the luxury of picking up their personal bottles roughly every 5km (~3.1 miles), making it easier to meet their fueling and hydration needs without carrying anything from the start. To facilitate running at such high speeds, elite runners do typically require a greater amount of carbohydrate and fluid to sustain their elevated outputs. For non-elite runners relying on standard aid stations, a lack of preparation can lead to missed opportunities to fuel and hydrate effectively.
\nMany runners make the mistake of not knowing where aid stations are located, leading to a panic when they realise they've run past one without grabbing anything. Others don’t anticipate the congestion at early aid stations, which can slow them down or cause them to miss their nutrition altogether.
\nHow to optimise your aid station approach:
\nA little preparation can make a big difference in ensuring you get the fluids and fuel you need.
\nRecommended reading: 4 tips for mastering water stations at a marathon
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