Reason I ask is because I am planning to essentially do OMAD but also allow myself a protein shake after the gym and some low calorie bevarages throughout the day (creamer in coffee, vitamin water, etc)
Is that messing anything up or is it really just calories in/out that matters?
I would say what you are describing isn’t Intermittent Fasting just a low-calorie diet. I wouldn’t think that any of the benefits of fasting would apply but you would probably lose weight if you are in a calorie deficit.
A lot of people in this community have shared their positive changes besides weight loss so for me it’s definitely more than calorie control.
On a general level, here are some baseline benefits of IF: https://www.healthline.com/nutrition/10-health-benefits-of-intermittent-fasting
IF works by clumping all calorie intake together, to send a false signal of abundance to the body, so that the body does not down-regulate metabolic rate to account for reduction in calories. This is why IF is superior to regular dieting as follows:
With your plan, you would disable this core principal, so you are basically just doing traditional calorie restriction, and missing out on the 2 above.
If gym is a big part of your plan here, you might want to try r/leangains instead. They specialize in tailoring IF for high gym workloads.