Chris91gp wrote: »

Exactly like the title states, when does keto stop? If I was to stay in keto for years when does my body run out of fat for fuel and my body starts to use lean muscle mass? Is there a body fat percentage that this would start at roughly?

Or can a person stay in keto for the rest of their life and be able to keep their muscle mass?

That is a perfectly logical question!

A couple thoughts ... First, as Steven Phinney points out, even elite distance runners have 100,000+ cal worth of fat in their portable pantries. But assuming you were to work it all off, you would replace your body fat with dietary fat and (belatedly) transition from weight-loss to maintenance, as @Cadori says. Phinney personally has been in ketosis for over two decades....

I'd like to recommend a couple resources for you (since you're the curious type!) - it is very helpful to have some go-to resources when you're starting this journey.

1. If you haven't stumbled across the LCD Launch Pad, I'd suggest you set aside a few hours and look through this great resource, which is maintained by @baconslave.
http://community.myfitnesspal.com/en/discussion/10103966/start-here-the-lcd-launch-pad2.

2. Stephen Phinney, Jeff Volek, Art & Science of Low Carbohydrate Living (technical) and New Atkins for a New You (popular) are great intros.

3, Phinney's YouTube vids are very informative. He explains that can take weeks to compete the transition from carb- to fat-burning. I'd recommend the JumpstartMD YouTube site, which has not only a long, comprehensive introduction to ketogenic diets by Phinney and Volek but also segments of the interview separated by topic.

Good luck!