Your mileage may vary: Training for a marathon on a vegan diet

Each time I run a marathon, I change one or two variables about how I train. I think of them as cards up my sleeve, or levers. Eventually I’ll run out of these low hanging fruits that drive step function improvement—as in, clear cut PRs—and the gains will be marginal. My biggest lever yet was switching to a vegan diet for the 2025 Flying Pig Marathon in Cincinnati.

I started eating mostly vegan in early February of this year. The point of this essay is how I think eating ~90% vegan improved my training and performance, but to gauge improvement you need a starting point. So I’ll start with the two marathons I ran before Cincinnati: Charlottesville and NYC. I’ve changed a couple variables each training cycle (e.g. changes to my sleep, fueling, pace, mileage) and there are a few more I have up my sleeve for future cycles (e.g. higher mileage, speed work). There are also variables that I think are distractions, like what shoes you wear¹. Feel free to skip past Charlottesville and NYC to read about my vegan experiment in Cincinnati.

Everyone is different, of course, and changing our habits is never a controlled experiment. I’m relatively new to this vegan world, and so I’m not trying to give heavy-handed advice. My experience is anecdotal, experimental. That is to say, I’ve been a happy camper running on a mostly vegan diet, but your mileage may vary.

Charlottesville, April 2021

Charlottesville 2021 was my first marathon. I’d been running mostly 3-6 miles per run from around 2015 when I started running through about 2020. That’s when I started running 10+ miles with some regularity. It was a rather hilly and isolated marathon course on dirt roads, through thick woods and alongside vineyards. Crowds were sparse because it was a pandemic year with a different course and a cap on runners.

I ran the whole thing with my brother Martin, who seemed to have an easier time despite dealing with unwanted bowel movements that called for several porta-potty pit stops. He’s six foot five and sturdy, so you wouldn’t think of him as having a runner’s build—more long haul truck than sporty racecar—but he’s a natural at putting one foot in front of the other for a long time. Those porta-pit stops may’ve had something to do with the ceremonial runner’s dinner of plain white pasta we ate the night before. High on glucose, low on fiber.

I ate a fairly balanced omnivore’s diet at the time. Plenty of salads and grain bowls for lunch and dinner, but also meat and dairy most days. I’d learned growing up to play sports on an empty stomach because otherwise I felt bloated and sluggish, and because my mom swore by it (she’d run a marathon on an empty stomach). I wouldn’t eat anything for hours before playing sports or running, and I wouldn’t drink any water on runs up to 10 miles or so. But during that C’ville training cycle my fueling burned me a couple times, most notably at the end of a 17 miler on a hot day in Richmond. I ran with Martin, and it was hurts-to-walk-barefoot-next-to-the-pool hot that day. We stopped once at a gas station for a Gatorade, but otherwise I don’t remember drinking anything. I hit a wall during the last couple miles and shuffled home nauseated. I couldn’t get down much food or water, and actually whatever food and water I had was coming up. I missed a Kendall Street Company concert that night at River City Roll to stay home throwing up.

That was my first big wakeup call on proper fueling and hydration, but even still I only had a bagel, Clif bar, coffee, and water the morning of the marathon. I had four or five Huma gels during the race, but it wasn’t enough. I depleted my glycogen stores and totally bonked somewhere after mile 20. The last several miles, mostly uphill, were brutal. I finished in 4:03:52².

New York City, November 2022

New York City 2022, in November, was my second marathon. It couldn’t have been more different from C’ville. 50k+ runners and millions of spectators. Totally electric. That day was unseasonably warm, and I couldn’t help but run a little faster than I should have in the first half what with all the strangers yelling my name (I was wearing a shirt that said “Peter” on the front and “...but my friends call me Pete” on the back) and friends posted up to cheer me on (my friend Spencer got too excited and kinda smacked me in the chest, which hurt). I ended up clocking 3:45:40³, despite super negative splits. I did hit a wall around miles 18-20 as the crowds thin out around the Bronx, and the last 10k was tough, but I drew enough energy from the city to finish it out.

I made two key improvements from C’ville to NYC: fueling and sleep. I started eating a big bowl of oats with fruit a couple hours before long runs, and usually also a Clif bar 30ish minutes before setting off. For early morning runs and race day I even started setting an alarm clock an hour or two before I woke up to wolf down my bowl of overnight oats and go back to sleep so that I could digest for a couple hours before running. I thought that sounded crazy when I first heard it on the Run4PRs podcast, but it worked well for me. Lots of glucose (and glycogen) in my system, but enough time for a bowel movement—with an assist from coffee—to feel light on my feet. I also started carrying water or making brief pit stops at bodegas to buy water, and I carried Huma gels on long runs.

The early morning oats might sound extreme, but it took another wakeup call before I started fueling more seriously. That one came after a spontaneous Sunday late afternoon 12 miler between Brooklyn and Manhattan with my friend Conway. I’d only eaten a bagel that day and likely not enough water. Dehydrated and depleted. It was a wonderful run, across the Brooklyn and Williamsburg bridges and wrapping up in McCarren Park by my shoebox Greenpoint apartment where we made dinner with my friend and roommate, Avery. Just as I sat down in front of my pasta with Conway and Avery, I fainted. I faceplanted onto my plate, then tipped backward in my chair and onto the hard tile floor of our kitchen. Luckily Avery and Conway were there to make sure I was ok, which I was. I ended up with a bump on my head and lesson learned (again) about fueling and hydrating before long runs.

Maybe just as importantly as fueling, for race day specifically, is how I adjusted my sleep. In Charlottesville I had to wake up well earlier than I was accustomed to for race day, and I remember experiencing that depleted feeling your body has when sleep deprived. It’s how you might feel when waking up super early for a flight. A cup of coffee helps mask it, but when pushing your body up to and past its learned limits, that’s not enough. So for NYC I gradually adjusted my alarm to the time I’d have to wake up on race day over the course of a couple weeks. By race day I was probably going to bed around 8pm and waking up at 4 or 5am.

Cincinnati Flying Pig, May 2025

Welp, I haven’t gotten around to writing up race notes nor finishing the meat of this essay, but I plan to do so before the ’26 Pig next May.

TL;DR until I come back to finish this: I ended up running 3:28:06⁴ and never really hit any wall. It was a fun race. I’d like to run it again. My endurance and recovery throughout training felt better than ever, probably because of my diet. I ate a lot of beets. Thanks to Scott Jurek and other (ultra)marathoners for leading the way on vegan running.

Footnotes

• For an elite runner, shoes probably make a difference. But for someone like me, shaving a few seconds off my mile pace is not going to move the needle compared to other variables, like diet. When it comes to finding the right shoe for me, I prioritize avoiding injury—not performance.
• 4:03:52 @ C’ville 2021. 9:19 mile pace. Same time as Martin who stuck with me despite stopping several times for unwelcome bowel movements. He could have broke four hours that day if he weren’t sticking with me, I think.
• 3:45:40 @ NYC 2022. 8:37 mile pace.
• 3:28:06 @ Cincy 2025. 7:57 pace.