If someone goes for so long without eating does their stomach reject food? after 30 days without eating anything, only drinking fluids, does your stomach reject food?

There : There is a syndrome associated with starvation called "refeeding syndrome". Your stomach doesn't "reject food", but after a prolonged time without food, your metabolism changes in order to accommodate the starvation. You start breaking down proteins and fats for energy instead of carbohydrates. This causes changes in your electrolyte balance and can occur even as quickly as 5 days with no food. Once the person starts eating again (usually after 4 days of eating), they can develop an electrolyte and fluid disturbance causing problems with the heart, lungs, and brain. In order to avoid these problems, starving people must be fed carefully paying special attention to their electrolyte balances. Milk is a great way to start since it contains many of the electrolytes needed along with protein, carbohydrate and fat. People who have been starving may also have stomach pains, reflux and nausea when starting to eat again, but this will pass with time and occasional treatment with antacids or motility agents.