People can eat grains just learn to moderate your habits. Whoops did I say moderate sorry I forgot most people can not do this.
As the population grows grain production will increase just like Silverback said, people will get fatter and unhealthier and be kept alive through advances in drugs and surgical techniques.
Therefore we should just kill of 90% of humanity and start again If I knew someone was going to be eating a lot of grains anyways I would recommend them eating wholegrains to improve their health. If I could get them off relying on grains altogether that would be best but that is highly unlikely to happen.