Complex sentence: Saponins are believed to be useful in the human diet for controlling cholesterol, but some (including those produced by the soapberry) are poisonous if swallowed and can cause urticaria (skin rash) in many people.
Split into simpler sentences: Saponins are believed to be useful in the human diet for controlling cholesterol. National Geographic Oct.1995, page 161 Some saponins (including those produced by the soapberry) are poisonous if swallowed and can cause urticaria (skin rash) in many people.