Zach Bitter — American ultramarathon runner and coach who has held multiple world records in the 100-mile run and 12-hour run. Known for low-carb/meat-based fueling and for racing fast on flat tracks; he was training for a transcontinental run across America.
The gist
Zach Bitter joins Lex Fridman to unpack what it takes physically and mentally to run 100 miles, from controlling the negative voice that wants to quit to the fine details of pacing on a 400-meter track. He explains his training philosophy built on a large aerobic base and the Maffetone 180-formula, and dives deep into low-carb and carnivore fueling, fat adaptation, and fasted training. The conversation covers his treadmill and track world records, his collaboration with Bert Kreischer, and his big upcoming goal: running from San Francisco to New York to raise money for charity. They also explore carbon-plate shoe technology, the future of human performance, and advice for finding your own path.
Big reveals
- Bitter's 100-mile track world record was 11 hours 19 minutes, later broken by Lithuania's Aleksandr Sorokin who ran 11:14, about 6:45 per mile.
- Bitter says he believes a human will break 11 hours for 100 miles within the next few years, roughly a 6:35 per-mile pace.
- His 100-mile treadmill record happened only because COVID cancelled every race in March 2020 and he live-streamed himself on a treadmill instead.
- Over 10 years of low-carb eating, his highest meat consumption in 2019 produced his best-ever racing season.
- He plans to run across America (San Francisco to New York), living out of an RV and averaging 70+ miles a day for about 42 days.
- He cites runner Kara Goucher possibly being the first to lose an Olympic spot due to a shoe technology disadvantage.
- Bitter, a former teacher who competed only at small Division III level, says he still second-guesses that running became his career.
Things worth remembering
- In ultrarunning a slow finish is called a 'death march' — finishing your first 100 even slowly gives you a mental template for the next one.
- The Maffetone (MAF) 180 formula: train at a heart rate of 180 minus your age to build aerobic base with low injury risk.
- The three biggest ultras are Western States 100, Ultra-Trail du Mont-Blanc, and the Comrades Marathon (technically 56 miles).
- At race pace Bitter burns about 80-90% fat, taking in only 15-40 grams of carbohydrate per hour to defend muscle glycogen.
- He deliberately varies which workouts are 'miserable' so training never becomes a uniform negative feedback loop.
- Bert Kreischer set a goal of running 2,000 miles in a year and once joined Bitter's treadmill livestream for over an hour.
- Carbon-plate 'super shoes' give an estimated 2-8% performance boost, and records have fallen across all distances since.
- The marathon world record pace is about 4:40 per mile — roughly a 70-second lap repeated over 26.2 miles.
- On a 100-mile track race you run extra distance passing slower runners in lanes two and three, which must be built into pacing.