The human body is incredibly resilient, and can last a long time without food — so long as it’s not dehydrated. Fasting for a few days is not harmful to most people as long as they drink plenty of water — which you’ll want to do anyway to trick your stomach into thinking you’ve eaten something.
However, people with some medical conditions should not fast under any circumstances. Diabetics, for example, need to regulate their blood sugar with food throughout the day. Consult your doctor before beginning a fast. Children, the elderly, pregnant or breastfeeding women, and people with chronic illness should not fast. Even otherwise healthy people will feel negative side effects while fasting. When you stop eating, your body doesn’t have an energy source; as a result, you will feel fatigue and dizziness. You may also feel nausea or suffer from constipation, and, obviously, you will feel very hungry. You may want to consider a clean eating cleanse instead. Focus on eating lean proteins, vegetables, fruit, nuts (i.e. almonds and cashews), and complex carbohydrates like sweet potatoes, brown rice, and quinoa, for at least 48 hours.