For how many days can a person survive without food?
If a person does not drink any water, they can typically last a week. However, once the body starts breaking down fat to produce ketone bodies for energy, it’s only about 13 hours before brain damage occurs. In other words, if you are going to go without food or need to re-energize your body from a fast via ketosis, drinking enough water is critical because otherwise your body will be in dire straits rather quickly. We’re talking half an inch of fluid loss (e.g., 8 cups of liquid) per day causes lethargy and 12% diminished daily physical performance—which is still better than 30% or more when dehydrated. So why would we even consider eating then?