i think about 1,5hrs is what Ken says (can't remember exactly now). but let's face it, we all have lives to live around the singing, so i end up eating just before singing sometimes, and at least for me, it works. i would also discern between an important show and a normal practice, where a burp or two aren't the end of the world (where even interrupting it because of being bloated would not be such a big deal). i guess everyone is different so this is only my opinion. also, it depends on the type of food. i would just experiment, if you can't do the recommended schedule. and then, best to know your body before an important gig.
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