We need food because it is the fuel our body uses to function properly and we need water because it keeps our cells hydrated, flushes out waste, keeps us cool and lubricates our joints. We cannot live without food and water. We can go without food for a long time. Most literature says 21 days without food is ok. Some people have gone for longer without any food. This is because our bodies store food in form of fat. When you don’t eat the stored fat is broken down to provide rule for your body. When the fat is finished the body starts to breakdown protein for fuel, that leads to wasting (e.g. in people with marasmus). If you stay very long without food, you will die because the body cannot function any more.
Water is more vital. A person can only go for a few days up to a week without water. If the temperatures are high they can only last 3 or 4 days without water. After that they die of dehydration.
As far as i know scientists have not found a way to sustain life without food and water. Maybe when you become a scientist you can do that research 🙂