Protein-energy malnutrition is a form of undernutrition caused by an extremely deficient intake of calories, protein, or both. Two examples of this type of malnutrition are kwashiokor and marasmus. Protein-energy malnutrition is more often caused by decreased absorption or abnormal metabolism. It is defined as a range of pathological conditions arising from coincident lack of protein and/or energy in varying proportions. The condition vary in forms ranging from mild through moderate to severe degrees.
If I'm not mistaken, it leaves through the osculum which is a cavity located on the upper part of a sponge.
Sponges feed through a process called filtration, which means that they filter the water in search of nutrients. And after they collect everything they need from the water, they need to let it out somehow; through the osculum.
Hope it helped,
BioTeacher101