Final answer:
Tapeworms lead to weight decrease because they absorb nutrients from the host's food, depriving the host of these nutrients.
Step-by-step explanation:
Tapeworms lead to weight decrease because they absorb nutrients from the host's food, depriving the host of these nutrients. Tapeworms can grow to be over 50 feet long and live inside the intestine of the host for several years, benefiting from the host's food. By taking in nutrients that would have been absorbed by the host, tapeworms can cause weight loss in the host.