The intestine is where all nutrients from food are sent into the body. When food leaves the stomach, it is mostly a liquid form containing dissolved nutrients. About 15-30 minutes after feeding, these nutrients are slowly absorbed through the wall of the intestine, like tea through a tea bag.
The wall of the intestine is basically a folded up filter, with enough area to cover half a badminton court, so it is very good at absorbing!
Some nutrients like amino acids (from protein); simple carbohydrates (like glucose); water soluble vitamins (e.g. vitamin C, B-vitamins); electrolytes (e.g. calcium, magnesium) get across very easily. Others, like fats, DHA, EPA, ARA, vitamins A, D, E, and K, need extra help, because they don’t dissolve well.
When kids become ill through a gut infection, the intestinal wall becomes leaky and loses the ability to absorb. Also, bacteria and viruses can enter the gut, disturb the balance of gut bacteria, causing diarrhea and gas. They can even get into the body and cause infections in other places.