This will depend on many other health factors as well. But some people can feel faint if they do not eat for a few hours and their blood sugar drops below a certain level.
I did the master cleanse for 10 days and felt great but you are still drinking. Make sure you use organic lemons and organic grade b maple syrup. I buy in bulk from the Fullar sugar family off ebay. You can use almost an entire gallon if you do it with another person or 1/2 gallon if you are single.
It depends on the person and the situation. When I was younger, I often skipped breakfast and lunch (which I don't recommend) and didn't eat until dinner without noticing any kind of difference in how I felt. Now, however, I don't feel very well if I skip breakfast. It does have to do with your blood sugar levels and for some people just a few hours will make them feel faint and ill.
I think, though, how much you drink might be even more important when it comes to how you feel. If you don't eat or drink for several hours, you'll feel much worse than if you only don't eat. People are often more dehydrated than they realize, and you can go longer without eating than without drinking.
Just as a side note...there's no proven benefit to things like the master cleanse, and reputable health and nutrition experts never recommend them...
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