Yes. I’ve done 48s consistently on a weekly basis with very good results for fat loss. I also know several people who regularly do 48s or longer every week and have been doing so for much longer than I have.
“Safe” depends on your state of health, but as a >65 guy w/ cancer it’s not hurting me a bit… in fact it seems to be helping.
I had attempted strict keto & ADF but could not manage the two combined. Too much willpower required. I am now eating LC (<50g net Carb daily) w/ a more-or-less normal protein & fat macro profile, and back to one \~40hr fast/week. This is now routine for 4 weeks & is doable.
In fact this past weekend I let the 40-ish continue to 54, then overnight to 64 then 70.5 hrs. Honestly I only ate Sun afternoon because of an expected busy Monday, and my sleep in >48hr fasts isn’t great.
OMAD plus one weekly 40+ is about golden for me. Muscle loss is a non issue: KEEP LIFTING, even on a fast day, and don’t short your protein on eating days.
Safe will depend on what you’re eating otherwise. Make sure you’re getting good nutritional variety and you should be fine save for personal health issues we don’t know about that you might have
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The goal should be to consistently restock all the nutrients and minerals you’ve used during the fast. Otherwise 48 hours a week and OMAD otherwise are entirely sustainable long term
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Just to say, too, I am OMAD full time. 5 day extended fast \~1 a month. And impromptu 48 hour fasts when I feel like I’m just not hungry at meal time (so I just skip until the next day)