Here is the only text in the Catechism that I can find that explicitly mentions gluttony, but it also links to
this text, which explains, with envy as an example, a little more about what it means. As one of the seven capital sins, "sins" are to be understood IMO in the context of the entire Catechism, which, in this context, means moral offenses. The Church distinguishes between the offense and the imputability of guilt for that offense. IOW, reading between the lines a bit (again, this is IMO only), the Church teaches to mind your behavior, and if you commit any grave matter (what would be, if you were susceptible to it, mortal sin), that you should confess it to the clergy. This is the Church's advice and counsel, for if you find yourself committing grave moral offenses. Her advice may appear to presume guilt, but I think that in fact it does not presume guilt, but does presume that you are dealing with a very spiritual thing now, and she would like to grant you some special, sacramental grace, to assist you in your struggle. Gluttony while a capital moral offense, does not appear to be grave matter, at least from what I understand, IMO.