Digestion has many ways of supporting immunity. The first is by providing nutrients that help maintain the immune system organs all over the body, and feeding the gut wall directly. The second is by feeding the bacteria of gut microbiome.
During times of illness, when the gut wall becomes leaky, loses nutrients and fluids at a much higher rate, and doesn’t work as well to absorb nutrients anymore . It also sheds more dead cells. So nutrient demand is slightly higher during these challenging periods.
This is what happens during diarrhea for example, and why children require electrolytes like potassium, calcium, magnesium, and soluble vitamins like B-vitamins and vitamin C. It is also why infants and children lose weight and growth can slow down during times of prolonged infections .
Prolonged undernutrition in developing countries is a major cause of stunting and is associated with increased levels of gut parasites .