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It really comes down to your fat percentage; BMI is only so and so good; but it’s better than nothing.
I’d say that extended fasting should be avoided if your BMI is bellow the normal weight range (18).
There are benefits from e.g. a 5 day fast but you need to have the necessary fat stored in your body - electrolyte ballance needs to be in check as well.
Then - how about sugary drinks? If you had these before your extended fast; you could be looking at withdrawal symptoms?
Starving =\= fasting. If you’re really hangry, you should eat. If it is not real hanger then you are fine.
Btw : most people will last 24hours just fine. Unless you have a medical condition or your body fat is too low.