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Comment by jniedrauer | Hacker News Reader

When I see studies like this, I always wonder if you might get the exact same benefits and more by just going for a run. When I run for more than 90 minutes without taking in carbs, my body goes into a ketogenic state very similar to a multi-day fast. And exercise has additional benefits that simply fasting doesn't.

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Kinda, but only indirectly as I understand it. The more I read the more it seems to matter the time spent in a fasting state relative to a fed state.

So a run could work if you’re not overeating, but if you’re regularly overeating it wouldn’t work because you might use up your food, but then immediately resupply or have eaten too much prior to it and it takes hours to finish nutrient delivery.

Mostly though they’re complimentary processes neither directly involved with the other.

The latest science in Rats says no. I don't have the exact article available but it's discussed at length in this podcast recently.

https://www.foundmyfitness.com/episodes/mark-mattson

As I’ve said in other comments what seems to matter is the ratio of time spent in a fed state (body delivering nurtrients) vs a fasting state (body using fat for energy, depleting stores of things and doing housekeeping).

From that perspetive running could help, but only from the point of view of possibly getting you to the fasting state more quickly (a kind of kickstarter), but it would be easy too derail that by eating to soon or a hundred other things.

Spent a few months reading about this stuff back in 2019 and basically concluded you can get roughly the same benefits from intermittent fasting / time restricted eating, caloric restriction and keto.

Fasting for 24-48 hours however triggers autophagy, which is quite significant; I don't think (but don't know if) you would get that from your runs.

You're definitely right about the many benefits of exercise, though. This is one of my favorite articles, and it only covers the benefits to the brain:

https://en.wikipedia.org/wiki/Neurobiological_effects_of_phy...

It helps with working memory, depression, self esteem, ADHD, alzheimer's, drug addiction, and the list just goes on and on...

When I was reading more about this most of the anti-aging benefits of fasting where explained by your body going into autophagy. I don't think just depleting your glycogen has the same effect and I didn't find any other reliable way of going into autophagy that didn't involve not eating for 36 hours.

Also a 90 minute run can have other side effects on people that just don't have the body for it. Even being fit and in my mid 20s and running with proper gear and on dirt and sometimes with a coach I developed plantar fasciitis in my 30s, I can do 10/15 minute runs and can hike and sky but I wouldn't risk a 90 minute run.

I don't have time (nor the endurance) for a 90 minute run, so could you combine the two? I often do a 14 hour fast and then go for a 20 minute run combined with some calisthenics on my lunchbreak before eating. How can you tell your body is in a ketogenic state?

I can definitely say the first few times I exerted a ton of energy after not eating for 12+ hours I felt like I had the flu for a few hours, but now I don't really get that.

They sell test strips that supposedly detect ketone bodies in urine although I don't know if they're reliable.

Personally my breath starts smelling like shit when I enter in ketogenic state.

>When I run for more than 90 minutes without taking in carbs, my body goes into a ketogenic state very similar to a multi-day fast.

That seems rather implausible. Do you actually test your ketones in both conditions, or is this just some subjective assessment?

I took this a subjective feeling of the experience, but I agree with you. It is almost literally impossible (some high level athletes can accomplish it, I believe, but not after 90 minutes) to actually enter a ketogenic state from exercise.

That is the normal state of ultra endurance athletes during long runs[0]. A lot of training stimulus is fat adaptation. Coaches will tell you that you begin to exhaust your glycogen stores beyond the 90 minute mark, and I can tell you subjectively that the body switches over around then. I have done fasted runs up to 3 hours before. Runs of that duration are physically impossible without burning fat as fuel.

[0]: https://www.tandfonline.com/doi/abs/10.1080/02640414.2019.17...

The full text of your link shows the athletes didn't have elevated ketones until the second day of the race. After 80km, or about 12 hours of running, on an energy deficit.

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