When I first started out IF a long time ago, I couldn’t go past 20 hours without feeling dizzy and nauseous. Plus I’m naturally prone to migraine, it became a bit debilitating.
I learnt that I needed more electrolytes (you can take it inside of the eating window), a lot more water (like a lot more!), and I needed to control the amount of carbs and sodium I’m taking in (especially processed food). As a chubbier person, I can feel and see when I have too much sodium, joints feel swollen and stiff.
I now don’t take electrolytes unless it’s longer than 24H, just a lot of water and very very mindful about controlling the amount of processed food I consume.
At the lowest level, migraine, dizziness and nausea is a sign of dehydration. If you make the tweaks but it still persists I would speak to a doctor about it. Don’t dismiss it.
My partner can’t do IF after trying for a consistent period of time. The doctor mentioned that it’s something to do with magnesium levels and anemic.
Drinking enough water and taking in electrolytes is definitely advised. But I also like to add that longer fasting times takes some getting used to. You should gradually increase your fasting time over weeks.
I’m currently doing OMAD (which is actually 23:1, not 20:4, unless it takes you 4 hours to eat a meal) and I feel completely fine with it now. I used to get headaches beyond 20 hours.
I have come to time-restricted eating by way of 1) gluten-free (celiac), then 2) keto, and now 3) time-restricted eating. I think I would never have been able to engage in TRE (maybe the same as your IF?) prior to those carb-reducing steps. I remember feeling so hungry I was nauseous if I skipped a breakfast accidentally. Now, I feel hungry here and there but I could just keep going if I felt like it.