I did an over-the-top version of intermittent fasting for about two months last year where I would fast (no calories, just water and black coffee/tea) for at least 24 hours and then would eat normally the following day and then fast again. So alternating >24 hr fasts with a day normal eating (3 normal meals).

During this experiment I felt mentally fantastic. Mood was improved. Energy was higher. Not to mention I spent way less money on food, spent way less time thinking about or having to find food on my fasting days, and felt more in control of my hunger.

I tried increasing my fast from 24 hrs to 48 hrs, it went fine. But when I broke my fast with a large bean rice and cheese burrito, I felt like I was dying about 30 minutes later (lightheadedness, tachycardia, nausea). Ended up being hospitalized with refeeding syndrome or something similar, which was surprising to physicians because they only saw refeeding syndrome (had critically low phosphate) in people who had gone without significant caloric intake for weeks or months at a time.

I’ve never been the same since then. I think Ive developed gastrocardiac syndrome because I frequently (1-2x week) get less severe episodes of nausea, lightheadedness and tachycardia that generally self resolve but still feels like I’m dying for about 30 minutes. It’s been about a year now, so seems somewhat permanent damage.

So, I definitely recommend intermittent fasting but if you have a tendency to take things to the extreme, just don’t. It’s not worth it.