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High Fat Diet for Ultra Marathons?

Any thoughts on whether Keto/High fat diets would be beneficial when running ultra marathons (100+ miles races)

My brother runs them as has complained that digestion i.e frequent bathroom breaks has been an issue when running longer races. He suspects that the fast acting carbs, gels, or just the constant refueling may be the issue and has been thinking if a higher fat diet or even going keto may help.

@mertdawg any input would be appreciated.

Have you even bothered to do a simple internet search on low carb for endurance performance? Names like Phinney, Volek, may jump out out at you because they have been publishing scientific data on this topic for years. If you genuinely want to help your brother spend a dollar or two on evidence-based books rather than looking for quick and lazy answers on a forum.

Good Keto Posts

This and your other post on Exogenous Ketone provide good information.

“…Quick and lazy answers on a forum”.

Unfortunately, the majority of lifters and population in general wants a simple answer from a complex question.

The preference is for a “Yes” or “No” answer. A sentence is the limit.


As you noted, there is plenty of information on the internet.

Volek and Phinney’s book, The Art and Science of Low Carbohydrate Performance is an excellent piece of work. It is a short read and a cheap book on amazon.

As you know, most of the research on the Keto Diet has been on endurance athletes.

A good piece of research on the Keto Diet for Strength Training is…

The Effects of Ketogenic Dieting on Body Composition, Strength, Power, and Hormonal Profiles in Resistance Training Males

Drs Jacob Wilson, Jeff Volek, Dom D’Agostino, etc Research Abstract is on the link above. I have the article, if you like to see it.

My Keto Diet Experience

Due to a heath issue, I’ve been on the diet for coming up on two years. I like the diet.

My training sessions are just as good on Keto as before.

Kenny Croxdale

Cheers Kenny.

I am aware of that study. I know Jacob Wilson’s credibility has come into question recently but still believe there is some validity around the idea of rapid fat regain when ‘large’ amounts of carbohydrates are introduced to ketogenic dieters. This is why I am not in favour of cyclical ketogenic diets or so-called ‘refeeds’ such as the kind Lyle McDonald advocates following aggressive diets.


I read something about that but since there no details on it, it hard to make any comment.

Rapid Fat Gain

I believe that there is rapid fat gain based on the information that Wilson has presented, as well as some personal experience with doing that once.

Cyclical Keto Diet

I followed the DiPasquale’s Anabolic Diet years ago. I am not an advocate of that method, either.

Kenny Croxdale