{"componentChunkName":"component---plugins-precisionhydration-src-templates-blog-blog-post-jsx","path":"/performance-advice/nutrition/how-marathon-runner-reed-fischer-trained-his-gut-to-consume-100g-of-carb-per-hour/","result":{"data":{"site":{"siteMetadata":{"title":"Precision Fuel & Hydration","siteUrl":"https://www.precisionhydration.com"}},"contentfulBlogPost":{"noIndex":false,"updatedAt":"2026-01-15T12:59:02.022+00:00","publishDate":"2026-01-15T00:00:00.000+00:00","title":"A practical guide to gut training (from an elite marathon runner)","customMetaTitle":null,"customMetaDescription":{"customMetaDescription":"Elite marathon runner Reed Fischer details his gut training protocol and shares a step-by-step guide for how to train your gut to consume more carb... ","childMarkdownRemark":{"html":"

Elite marathon runner Reed Fischer details his gut training protocol and shares a step-by-step guide for how to train your gut to consume more carb...

"}},"slug":"how-marathon-runner-reed-fischer-trained-his-gut-to-consume-100g-of-carb-per-hour","blogTags":"Nutrition","featuredPost":false,"author":{"name":"Reed Fischer","slug":"reed-fischer","facebookHandle":null,"twitterHandle":null,"instagramHandle":"https://www.instagram.com/reedfisch/?hl=en","linkedInProfile":"https://www.linkedin.com/in/reedfischer1/","stravaProfile":null,"bio":{"childMarkdownRemark":{"html":"

Reed is an elite 2:10 marathon runner who's one of the top performers in the USA. He's finished in the top-10 at World Marathon Majors, the US Olympic Marathon trials, and won the Chicago half marathon.

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He helped found the team that he currently trails with, Tinman Elite, and has coached multiple marathon runners to Boston Qualifying times, personal bests and through their debut marathons.

"}},"title":"Elite Marathon Runner and Coach","headshot":{"file":{"url":"//images.ctfassets.net/428xzyjdw7rf/73QnYn7sTYnfIf48uKa0mw/65fd7285be00af5b58afbc45e19dfdd3/Reed_Fischer_author_roundel.png"}}},"scientificallyReviewed":null,"image":{"resize":{"src":"//images.ctfassets.net/428xzyjdw7rf/57m8uySirbMQSH5qLLYg4x/bd51bdadbdfc819e3ea40fa41cf505d3/PF_30_Gel_blog_header__Credit_PF_H_.webp?w=1200&h=630&q=70&fit=fill","width":1200,"height":630}},"socialMediaImage":null,"body":{"childMarkdownRemark":{"excerpt":"2025 was the year of ‘High Carb’ in endurance sport. Everywhere you turned, it seems there’s a pro triathlete crushing 100g of carb drink directly before going…","html":"

2025 was the year of ‘High Carb’ in endurance sport. Everywhere you turned, it seems there’s a pro triathlete crushing 100g of carb drink directly before going to sleep, an ultra runner downing a 90g carb gel in 0.2 seconds, or an elite marathoner eating microwaveable rice at the expo (looking at you, CJ), all in the name of increasing carb intake.

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Despite the prevalence of ‘high carb’ as a buzz word, limited information on the subject and how it applies for the world outside of professional spheres can make it feel a bit like the Wild West at times. Instead of tumbleweeds blowing through, it’s empty gel wrappers (here’s your reminder to leave no trace, folks). 

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So, how can you increase your gut tolerance to hit your ideal carb numbers without needing to access the public restrooms on your route? Gut training.

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My gut training guide

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Gut training is exactly what it sounds like. Just in the same way that I train my legs and mind with hundreds of miles of training runs, race-specific sessions, strength work, and visualizations over the course of a marathon training block, I’m also training my stomach to handle increased carb intake. 

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And, in the same way I don’t run my highest mileage week at the start of the build and then try and survive, I’m not starting out with 100+ grams of carb per hour and hoping for the best.

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Here’s a quick and dirty gut training guide that I suggest the athletes I coach follow (and that I’ve used myself in training for World Marathon Majors and the 2025 World Championships Marathon in Tokyo):

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  1. Start at 30g of carb per hour/session roughly 12 weeks out from race day. That’s one PF 30 Gel during your mid-weeker, and maybe two PF 30 Gels on a long run to start
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  2. From here, aim to add about 10g of carb per hour each week
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  3. So, Week 2 is 40g per hour/session, Week 3 is 50g per hour/session, and so on
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  4. Continue this progression until you’ve reached your target carb intake. For most people that’ll be about 80-100g per hour
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  5. Staying on track with this progression means you’ll reach your target numbers about four weeks out from your goal race. So, there’s plenty of time to work out any potential kinks and you can use the time to enjoy multiple efforts in different conditions to make sure your plan is dialed
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Image Credit: Joe Hale ©

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How I trained my gut for World Marathon Champs

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Curious to see exactly how I executed this gut training plan en route to 28th place at the absurdly hot and humid 2025 World Athletics Championships Marathon in Tokyo? Here you go:

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Week 1: 

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Week 2:

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Week 3:

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Week 4:

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Week 5:

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Week 6:

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Week 7:

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Week 8:

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Week 9:

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Week 10:

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Week 11:

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Week 12:

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Race:

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Key takeaways

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There you have it! 12 weeks of physical, mental, and gut training to cross the line 28th at my first World Marathon Championship. I started small, at just 30g of carb per hour in the first week of training, but had a four-week stint where I was hitting about 100g of carb per hour. Hitting those numbers fairly comfortably in training helped build give me confidence that I could manage 100g+ per hour on race day. 

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A trend you may have noticed: I leaned heavily on gels during my mid-week sessions, and fluids heavily on long run days. Gels make for a more convenient and portable option, but I wanted to simulate the extra fluid intake that the weather in Tokyo would demand during long runs. 

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Make sure you’re practicing a strategy that lines up with what you expect on race day. Hotter, more humid conditions? Heavier or saltier sweater? Maybe consider getting some of your carb through drink mixes. Cool, comfy day? Not much of a sweater? Gels are probably the more convenient option in training and on race day.

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There’s your crash course in gut training in today’s high carb world. You’re ready to head into your training block with a head full of steam and a belly full of fuel!

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Further reading

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