Get latest updates from a collection of database entries (Mongodb, Mongoose)

I am trying to create a newsfeed and I am trying to conjure up the best way (or algorithm in a sense) to get a bunch of Objects a user is subscribed to in with mongoose and then return the latest updates ordered chronologically from all those objects:

ie. with mongoose schemas:

var UserSchema = new Schema({
    subscribed: [ObjectSchema]
  });

var ObjectSchema = new Schema({
    updates: [UpdateSchema]
});

var UpdateSchema = new Schema({
    date_updated: Date,
    message: String
});

Thanks in advance!