Had my gall bladder out many years ago and experience this as well.
I try to use a digestive enzyme pill especially when eating a meat-heavy meal. It helps somewhat.
Also tried to regulate with a bowl of oatmeal in the morning but that doesn’t work well if you’re fasting in the morning.
Hope you can come up with a solution.
Got mine taken out in 2014 and have suffered with LBM too for quite a while until 2017. Then it just resolved by itself. I noticed fatty foods made my LBM worse (though I’m able to tolerate them now as long as I take probiotics). So maybe try to play around with what food works for you. I haven’t been on IF then but am now and I break my fast with a probiotic drink then pretty much anything I want to eat with no problems.
Edit: I’m on 16:8 from 10am to 6pm
I had mine out like 4 years ago and still need to be near a bathroom 15 minutes after eating. That’s my favorite part of IF is less diarrhea because less eating haha. Thanks to the comments I have some things to try. I guess I had just thought I would have to live with it. Best of luck to you!