From a previous question about this:
"Lecithin is an ingredient found in almost all, if not all protein-based drinks. As I recall, it helps the powder mix with liquid (so it doesn't form a solid island on top of your milk or water).
This lecithin is derived from soy but it has nothing to do with soy protein or the isoflavones in soy we advise people to avoid."
That search engine is magical sometimes!