Long before we'll get most people to watch what they eat, we'll have inexpensive, tasty, 'lab grown' meat that uses drastically less water to create. That'll be commercially available within 15-20 years. Soy as a replacement will never end up being a necessity, technology and ingenuity will once again fix our problems.
I wonder when we will finally admit that we need to watch what foods we consume. Casava instead of rice, soy instead of meat, etc.