Switching between fat and glucose metabolism requires an adjustment period, analogous to getting rust off railroad tracks.

“if you've been going down the fat path all the time and there's the little lever you would pull the conductor would jump out pull the lever and to go to the glucose side well if you don't use that lever for a while it gets rusty right so that conductor's got to jump off he's got to pull that lever and he's got to get some wd-40 and he's got to get that get that lever switching and then eventually if that lever is switched back and forth enough it doesn't need the deep wd-40 anymore you're switching that lever back and forth you can start kind of in essence that somewhat describes metabolic flexibility to a certain degree but it's the same thing it's that glucose intolerance that all that people get freaked out about with keto where they say oh my gosh i'm gonna make myself glucose intolerant that is a temporary thing and exactly what your body should be doing and basically all you're just getting the rust off the railroad tracks a little bit”