I drink a protein shake with OMAD as I am vegetarian and I wasn’t meeting my macros and calories without it.
That being said, I drink it during my eating window along with my meal.
If you do it outside of your window, it will for sure break your fast
I wouldn’t jump straight to OMAD. Start off with 16 hours and work your way up to OMAD. That way it’s not such a big shock to your system and likely you’ll be more successful in your IF journey.
I was able to do this fairly easily for 8 months.
I started with keto. Then I started tracking my schedule. For one week, I wrote down everything I did so I could see how I was using my time. I gave myself a schedule based on what I was already doing naturally, and added time for some new hobbies.
I would break my fast at 8am with coffee with cream, then a keto meal of ~1600kcal between 11am-12pm. I still consider that OMAD.
I would be fine until around 7-8pm when I would have some tea. Went to bed usually at 10-11pm. Up around 5:30-6am.
Having the schedule made a huge difference. I could see how much time and mental energy I was saving by having just the one meal. I could also see exactly where all that free time and energy was going.
Good luck!
In my experience, OMAD is much harder if I only do it some of the time. When I first started, I worked up to it — gradually increasing my fasting hours until it started to be easy to delay breaking my fast until dinnertime. Now it’s no longer a problem if I occasionally have a day or week when I am not practicing IF (because of intense physical activity — backpacking, etc.), but that would not have worked for me when I first started.
Take water on your break or black coffee. If you’re going to eat 1 meal that day then do exactly that. Get curious with how you body responds to that and don’t search for hacks. It’s your willpower vs your old habits, aim to win. Understand that old habits got you into this and breaking them is probably a good thing, even if it feels really awkward at first. Stay curious and give it a few weeks test, if after that feel too restricted try 16:8, you want to feel like it’s something you can maintain, the trick is find what works with your body and your schedule.