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Ultrarunner Zach Bitter Keto Diet

Zach Bitter keto diet propels him to record

Zach Bitter is an ultramarathoner who recently broke the hundred-mile treadmill running record when he ran the distance in a time of 12 hours, 9 minutes and 15 seconds. That works out to a jaw-dropping 7:18 minute mile pace for the 100 miles.

Zack Bitter has been a low carb/high fat advocate in the ultramarathon community for quite some time. He did start off as a typical high carb endurance athlete but notice back in 20 1030 is having issues with poor sleep any attributed to his high carbohydrate diet.

Bitter had previously broken the indoor track hundred-mile record with an 11 our 90 minute and 13 seconds record in fall 2019, averaging a 6:48 minute mile pace to set the record.

His nutrition during the hundred mile treadmill run was essentially just water and electrolytes with a small bag potato chips towards the end of the run as well as an 8 ounce soda.

Zach had a chance meeting with Dr. Jeff Volek, a ketogenic and sports performance researcher who turned Bitter onto the low carb/high-fat diet for endurance athletes.

Bitter made the switch in the off-season and said it took about one month for him to feel as if he was truly fat-adapted and where he didn’t feel the need to consume much in the way of any carbohydrates during his runs. Zach also has said it took almost two years for the high fat keto diet to really click with him from a performance standpoint.

His diet consists mostly of whole foods such as grass fed beef and Bitter gets about 10% of his macros from carbohydrates. However, he does vary his carbohydrate percentage based on his training . Zach says he can go anywhere from zero carbohydrates to 30% carbohydrates in any given week depending on his training load.

He finds that he does much better on the low carb/high fat diet with more consistent energy throughout the day were before on the higher carb diet he was noticing energy crashes occasionally through the day.

Zach Bitter on nutrition, ketosis and carbs

What I found interesting was Zach’s view of using carbs as an added energy boost on top of his fat-adapted body. He views using carbs during a run the same as other endurance athletes view caffeine, something to give them an added boost during a hard workout. Bitter is careful to limit the amount and frequency of when and how he takes carbohydrates so that he can continue to depend mostly on fat for fueling his runs.

Find out more about Zach at

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