Final answer:
Diets high in protein can prevent or cure pellagra because protein-rich foods often contain high levels of tryptophan, which is converted into niacin in the body, mitigating the risk of niacin deficiency.
Step-by-step explanation:
The fact that the amino acid tryptophan can be converted to niacin by the body helps to explain why diets high in protein could prevent or cure pellagra. Pellagra is a deficiency disease caused by a lack of niacin, and it is characterized by the '3 Ds': Dermatitis, Diarrhea, and Dementia. With 60 mg of tryptophan converting into 1 mg of niacin, foods rich in tryptophan can have a sparing effect on the body's niacin requirements. Therefore, because protein-rich diets often contain high levels of tryptophan, they are likely to prevent niacin deficiency and subsequently pellagra.
Option B is incorrect as corn-based diets generally lack niacin and therefore do not prevent pellagra. Gelatin, as mentioned in option C, does not cure pellagra because it is not a good source of tryptophan and hence, does not significantly contribute to niacin biosynthesis. Option D is unrelated to niacin or tryptophan and instead refers to Wernicke-Korsakoff syndrome, which is associated with thiamine deficiency commonly seen in alcoholics.