I-II, Q. 102, A.
6, ad 1]. It is the inordinate desire of food that defiles a man
spiritually.

Reply Obj. 2: As stated above, the vice of gluttony does not regard
the substance of food, but in the desire thereof not being regulated
by reason. Wherefore if a man exceed in quantity of food, not from
desire of food, but through deeming it necessary to him, this
pertains, not to gluttony, but to some kind of inexperience. It is a
case of gluttony only when a man knowingly exceeds the measure in
eating, from a desire for the pleasures of the palate.

Reply Obj. 3: The appetite is twofold. There is the natural appetite,
which belongs to the powers of the vegetal soul. In these powers
virtue and vice are impossible, since they cannot be subject to
reason; wherefore the appetitive power is differentiated from the
powers of secretion, digestion, and excretion, and to it hunger and
thirst are to be referred. Besides this there is another, the
sensitive appetite, and it is in the concupiscence of this appetite
that the vice of gluttony consists. Hence the first movement of
gluttony denotes inordinateness in the sensitive appetite, and this
is not without sin.
_______________________

SECOND ARTICLE [II-II, Q. 148, Art. 2]

Whether Gluttony Is a Mortal Sin?

Objection 1: It would seem that gluttony is not a mortal sin. For
every mortal sin is contrary to a precept of the Decalogue: and this,
apparently, does not apply to gluttony. Therefore gluttony is not a
mortal sin.

Obj. 2: Further, every mortal sin is contrary to charity, as stated
above (Q. 132, A. 3). But gluttony is not opposed to charity, neither
as regards the love of God, nor as regards the love of one's
neighbor. Therefore gluttony is never a mortal sin.

Obj. 3: Further, Augustine says in a sermon on Purgatory [*Cf.
Append. to St. Augustine's works: Serm. civ (xli, de sanctis)]:
"Whenever a man takes more meat and drink than is necessary, he
should know that this is one of the lesser sins." But this pertains
to gluttony. Therefore gluttony is accounted among the lesser, that
is to say venial, sins.

Obj. 4: _On the contrary,_ Gregory says (Moral. xxx, 18): "As long as
the vice of gluttony has a hold on a man, all that he has done
valiantly is forfeited by him: and as long as the belly is
unrestrained, all virtue comes to naught." But virtue is not done
away save by mortal sin. Therefore gluttony is a mortal sin.

_I answer that,_ As stated above (A. 1)