Kwashiorkor disease is caused by a deficiency of -

Kwashiorkor is a severe form of protein deficiency disease, commonly seen in children who receive sufficient calories but inadequate protein in their diet.

Symptoms of Kwashiorkor:
Swollen abdomen (pot belly)
Edema (swelling of feet and face)
Stunted growth
Muscle wasting
Skin and hair changes

It is mainly caused by a lack of protein in the diet.

Therefore, the correct answer is Protein.