It is a concern, but not at 3 days.It can happen when there has been extended fasts of typically 5-7 days.But there are a whole host of factors, health, weight, nutrition, speed of kcal intake after fasting.
As another has said, it isn’t something you should be worried about, but it is also something to be aware of.
Have small meals often after a fast.
Here is a link to a 2009 journal, old I know, but it gives you some idea of what to look out for, people who are at risk, and hopefully some peace of mind that it is highly unlikely to happen.
Refeeding syndrome seems a little exaggerated in this sub and this question pops up at least once a week.
It can occur in severely undernourished persons - persons that are starved, malnourished (queue to the commercials you see of starving children in 3rd world countries), anorexics, etc.
From what I’ve read in fasting literature, you don’t need to be concerned with it on 5 day or less fasts – and even than it’s rare.
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