Read our 2022 Western States 100 results article to find out what happened at the front of this year’s Western States 100.

Low Carbohydrate Training

A discussion of long training runs with little-to-no carb intake, including bonk runs.

By on July 25, 2011 | 57 comments

I’ve been running here in Colorado’s San Juan Mountains for three weeks. Most of my runs have been low-intensity hike up/run down efforts lasting from two and a half to five hours. I’ve consumed calories during only two runs – a cup of veggie broth while pacing at Hardrock and roughly ten gels as well as a good deal of sports drink during the Kendall Mountain Marathon. A small part of the reason behind this was to shed a couple extra ounces here and there before UTMB, but the main reason behind the move was to work on my body’s ability to utilize fat as an energy source during the same race. While this ability would greatly benefit me during any long ultra, it’ll be even more important at UTMB where I’ll only have one spot halfway through the race where I can restock my gels, which are normally the vast majority of my in-race calories.

Although much recent training advice has been toward runners fueling throughout their long training bouts, this sort of low-to-no carb training isn’t without precedent. I’m sure many ultrarunners and other endurance athletes have done this by default. I’ve much enjoyed this low-carb training article from First Endurance when I read it a few years ago and again now for its presentation of research on low-intensity, low-carb training.

While I’ve not been engaging in the practice, the article suggests not replenishing glycogen stores via carbohydrate consumption prior to some of these low-intensity, low-or-no card training sessions. Years ago, I heard of some top New England ultrarunners (if I remember correctly, Todd Walker and, maybe, Leigh Schmitt) occasionally running back-to-back “bonk runs” on the weekend in which they’d go long at a moderate-to-hard effort on Saturday with no carb intake, refraining from refueling with carbs afterward, and then running moderately long again on Sunday in an already glycogen-deleted state.

I will continue to ingest carbs, usually as GU energy gels, during races (I ate 30+ GUs during Western States) and higher intensity long runs. I’ll also continue to bring carb sources with me during all of my long runs as an emergency backup. However, I’ve enjoyed my no fueling experimentation this month as well as my low-carb long run training throughout this spring and summer. I think it’s too early to tell if it’ll result in a major performance boost on race day, but I don’t feel like my low-carb training plan has hampered me in the least the past few weeks.

Call for Comments
Do you always fuel during your long training runs? Do you ever restrict your carb intake during training runs? Do you routinely use such a restriction?

It’d be great to hear your reasons for whatever level of carbs you use during training.

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Bryon Powell

Bryon Powell is the Editor-in-Chief of iRunFar. He’s been writing about trail running, ultrarunning, and running gear for 15 years. Aside from iRunFar, he’s authored the books Relentless Forward Progress: A Guide to Running Ultramarathons and Where the Road Ends: A Guide to Trail Running, been a contributing editor at Trail Runner magazine, written for publications including Outside, Sierra, and Running Times, and coached ultrarunners of all abilities. Based in Silverton, Colorado, Bryon is an avid trail runner and ultrarunner who competes in events from the Hardrock 100 Mile just out his front door to races long and short around the world, that is, when he’s not fly fishing or tending to his garden.