Tom Rowland Podcast Episode 498 is my conversation with ultramarathon runner Zach Bitter, a former world-record holder in the 100-mile and 12-hour run. Zach is one of the most thoughtful endurance athletes I have talked to, and we get into what it really takes to run 100 miles: how he fuels with a low-carb, fat-adapted approach, how he built metabolic efficiency over years of training, and how he keeps his mind in the right place when the body wants to quit.
▶ Watch on YouTube · 🎧 Listen now
Zach Bitter is an American ultramarathon runner who has held world records for the 100-mile run and the 12-hour run. He is known for his fat-adapted, low-carbohydrate approach to endurance fueling and for being an articulate voice on metabolic efficiency, pacing, and the mental side of running extremely long distances. He also coaches athletes and shares his training methodology widely.
Zach uses a low-carbohydrate, fat-adapted approach that he built over years of training his body to burn fat efficiently at race pace. Rather than relying on a constant stream of sugar, he trains his metabolism to draw on fat stores, which stabilizes energy over very long efforts. He still uses some carbohydrate strategically, but the foundation is metabolic efficiency developed through consistent training and diet.
Metabolic efficiency is the ability to burn a higher percentage of fat for fuel at a given intensity, sparing limited carbohydrate stores. For an ultramarathoner, this matters because the body can only hold a small amount of glycogen, while fat stores are effectively unlimited. Zach explains how training the body to tap fat keeps energy steadier across a 100-mile race and reduces the crashes that come from depending on sugar.
Zach treats the mind as a trainable part of endurance, not an afterthought. He breaks enormous efforts into manageable pieces, stays present rather than fixating on the finish, and accepts that low points are part of the process rather than signs to stop. In the episode he describes how he works through the inevitable dark stretches of an ultramarathon.
Yes. Zach's principles — building an aerobic base, improving metabolic efficiency, fueling deliberately, and managing the mind — scale down to any athlete who wants to go farther. You do not have to chase a 100-mile record to benefit from training your body to burn fat and pacing your effort intelligently. He talks through how a normal person can apply the same ideas.
Tom Rowland Podcast Episode 498 with Zach Bitter is available on Apple Podcasts, Spotify, YouTube, and wherever you get your podcasts. The video version is embedded at the top of this page.
I came into this one as a student. I train, I push myself, and I have my own theories about endurance, but Zach has actually run 100 miles faster than almost anyone alive and set world records doing it. When he talks about fueling or metabolic efficiency or the mental game, he is not pulling it from a blog — he is pulling it from inside the work. I wanted him to walk me through how a human being runs that far, and the parts that landed hardest were the ones about training the body to burn fat instead of sugar.
Zach has lived the full arc of a 100-mile race more than once, and he describes what the body goes through across those hours better than any chart could. He talks about energy systems, the limits of glycogen, and why fat becomes the fuel that matters when the distance gets absurd. The physiology is fascinating, and he makes it understandable. Press play to hear him break it down.
The conventional wisdom for endurance is to load carbohydrates, so Zach's fat-adapted approach surprised a lot of people. He explains why he trained his body to burn fat at race pace, what that does to his energy stability, and how he still uses carbohydrate strategically. It is one of the most counterintuitive parts of the conversation. Watch the YouTube player above for the full reasoning.
Metabolic efficiency is not something you switch on the week before a race — Zach built it over years. He walks through how training and diet together teach the body to tap fat stores and spare carbohydrate, and why that is the real engine behind his records. If you care about going farther on less, this is the section to listen to.
▶ Watch the full conversation on YouTube · 🎧 Listen now
Every ultramarathon has dark stretches, and Zach treats the mind as something you train just like the legs. He talks about breaking the distance into pieces, staying present, and accepting low points instead of fighting them. The mental framework he describes applies far beyond running. Listen to that section of the episode.
You do not have to run 100 miles to use what Zach knows. He scales the principles down — aerobic base, fat adaptation, deliberate fueling, and a trained mind — for anyone who wants to push their own ceiling. I asked him directly how a regular person should start. Press play in the player above for his answer.
The day after talking to Zach, the idea I kept turning over was that the body is far more adaptable than we give it credit for. He trained his metabolism to do something most people assume is impossible, and he did it patiently, over years.
What I take from Zach is that endurance is built, not given. The fat adaptation, the pacing, the mental discipline — none of it is a trick. It is the slow accumulation of doing the work, which is exactly the lesson that applies to training, business, and just about everything else.
▶ Watch the full conversation on YouTube · 🎧 Listen now
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Zach Bitter is an American ultramarathon runner and coach who has held world records for the 100-mile run and the 12-hour run. He is widely recognized for his fat-adapted, low-carbohydrate approach to endurance fueling and for his clear thinking on metabolic efficiency, pacing, and the psychology of running extremely long distances. He coaches athletes and shares his training philosophy through his work in the endurance community.
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