They would be refering to the inulin content. For example the eddo (root of the taro) contains inulin and is extremely toxic uncooked. You have to peel them with gloves on, soak in water overnight, throw out the gloopy/gel water, cook like a potato and then it is perfect, and safe to consume. The body can't digest inulin, it passes through to the colon, where it ferments...