And, technically, this parasitic infection, called taeniasis, does cause weight loss. “Tapeworms will cause you to lose weight because you have this huge worm in your intestines eating your food,” Quinlisk says.

Why do you lose weight with a tapeworm?

The tapeworm diet works by swallowing a pill that has a tapeworm egg inside. When the egg eventually hatches, the tapeworm will grow inside your body and eat whatever you're eating. The idea is that you can eat whatever you want and still lose weight because the tapeworm is eating all your “extra” calories.

When were tapeworms used for weight loss?

Tapeworm diet. Not for the squeamish, in the early 1900s the tapeworm diet started to be advertised, says Foxcroft. Many years later the opera singer Maria Callas was reported to have eaten the parasites to try and lose weight, but it's since been suggested that this was the stuff of myth.