Right from Meteor documentation:
Meteor.publish("userData", function () {
return Meteor.users.find({_id: this.userId},
{fields: {'other': 1, 'things': 1}});
});
And also:
Meteor.publish("allUserData", function () {
return Meteor.users.find({}, {fields: {'nested.things': 1}});
});
Hope this helps.