Laudator Temporis Acti

4 Maccabees 1.25-27:

In pleasure there exists even a malevolent tendency, which is the most complex of all the emotions. In the soul it is boastfulness, covetousness, thirst for honor, rivalry, and malice; in the body, indiscriminate eating, gluttony, and solitary gormandizing.

ἐν τῇ ἡδονῇ δὲ ἔνεστιν καὶ ἡ κακοήθης διάθεσις, πολυτροπωτάτη πάντων οὖσα τῶν παθῶν, καὶ τὰ μὲν ψυχῆς ἀλαζονεία καὶ φιλαργυρία καὶ φιλοδοξία καὶ φιλονεικία καὶ βασκανία, κατὰ δὲ τὸ σῶμα παντοφαγία καὶ λαιμαργία καὶ μονοφαγία.

See also 4 Maccabees 2.7:

Otherwise how could it be that someone who is habitually a solitary gormandizer, a glutton, or even a drunkard can learn a better way, unless reason is clearly lord of the emotions?

ἐπεὶ τίνα τις τρόπον μονοφάγος ὢν τὸ ἦθος καὶ γαστρίμαργος ἢ καὶ μέθυσος μεταπαιδεύεται, εἰ μὴ δῆλον ὅτι κύριός ἐστιν τῶν παθῶν ὁ λογισμός;

Solitary gormandizing is μονοφαγία (monophagía), and the solitary gormandizer is μονοφάγος (monophágos). These Greek compounds come from μόνος (mónos) = alone and φαγεῖν (phageîn) = to eat. The superlative μονοφαγίστατος (monophagístatos) occurs in Aristophanes' Wasps (922-923, trial of the dog Labes, tr. Alan H. Sommerstein):

So don't you let him off, because he's also, of all dogs alive, by far the worst man for solitary eating.

μή νυν ἀφῆτέ γ᾽ αὐτόν, ὡς ὄντ᾽ αὖ πολὺ
κυνῶν ἁπάντων ἄνδρα μονοφαγίστατον.

What's wrong with the solitary eater is not so much the mere fact that he dines alone, but that he doesn't share his food with others. Juvenal in his first satire (lines 127-146, tr. G.G. Ramsay) criticizes the rich patron for not sharing his sumptuous meal with his clients:

The day itself is marked out by a fine round of business. First comes the dole; then the courts, and Apollo learned in the law, and those triumphal statues among which some Egyptian Arabarch or other has dared to set up his titles; against whose statue more than one kind of nuisance may be committed! Wearied and hopeless, the old clients leave the door, though the last hope that a man relinquishes is that of a dinner; the poor wretches must buy their cabbage and their fuel. Meanwhile their lordly patron will be devouring the choicest products of wood and sea, lying alone upon an empty couch; yes, at a single meal from their many fine large and antique tables they devour whole fortunes. Ere long no parasites will be left! Who can bear to see luxury so mean? What a huge gullet to have a whole boar—an animal created for conviviality—served up to it! But you will soon pay for it, my friend, when you take off your clothes, and with distended stomach carry your peacock into the bath undigested! Hence a sudden death, and an intestate old age; the new and merry tale runs the round of every dinner-table, and the corpse is carried forth to burial amid the cheers of enraged friends!

ipse dies pulchro distinguitur ordine rerum:
sportula, deinde forum iurisque peritus Apollo
atque triumphales, inter quas ausus habere
nescio quis titulos Aegyptius atque Arabarches,
cuius ad effigiem non tantum meiere fas est.
vestibulis abeunt veteres lassique clientes
votaque deponunt, quamquam longissima cenae
spes homini; caulis miseris atque ignis emendus.
optima silvarum interea pelagique vorabit
rex horum vacuisque toris tantum ipse iacebit.
nam de tot pulchris et latis orbibus et tam
antiquis una comedunt patrimonia mensa.
nullus iam parasitus erit. sed quis ferat istas
luxuriae sordes? quanta est gula quae sibi totos
ponit apros, animal propter convivia natum!
poena tamen praesens, cum tu deponis amictus
turgidus et crudum pavonem in balnea portas.
hinc subitae mortes atque intestata senectus.
it nova nec tristis per cunctas fabula cenas;
ducitur iratis plaudendum funus amicis.

If I'm not mistaken, Leopardi somewhere in his Zibaldone discusses solitary eating, but I can't put my finger on the passage.