The artist Claude Lantier, the most sympathetic character in Zola's Le Ventre de Paris, explains to Florent, the protagonist, that there is a battle being fought between the Fats (almost all the members of the community of Les Hslles) and the lean outsiders like Claude and Florent). the refusers of try feats.
Claude takes off from a description of a set of engravings (by Breugel?)
— Est-ce que vous connaissez la bataille des Gras et des Maigres ? demanda-t-il. Florent, surpris, dit que non. Alors Claude s’enthousiasma, parla de cette série d’estampes avec beaucoup d’éloges. Il cita certains épisodes : les Gras, énormes à crever, préparant la goinfrerie du soir, tandis que les Maigres, pliés par le jeûne, regardent de la rue avec la mine d’échalas envieux ; et encore les Gras, à table, les joues débordantes, chassant un Maigre qui a eu l’audace de s’introduire humblement, et qui ressemble à une quille au milieu d’un peuple de boules. Il voyait là tout le drame humain ; il finit par classer les hommes en Maigres et en Gras, en deux groupes hostiles dont l’un dévore l’autre, s’arrondit le ventre et jouit. - Pour sûr, dit-il, Caïn était un Gras et Abel un Maigre.All of this fits in with the action of the novel. Claude states that the Fats hate even the sight of the Leans, witness Florent's treatment by the fishmongers, who act like cats driving out a mouse. That Florent is little interested in money and even less in eating more than he needs to survive marks him out as an enemy of society.
Are you familiar with the the battle of the Fats and the Leans? he asked. Florent, surprised, says that he didn't. Then Claude became enthusiastic, spoke about this series of engravings with high praise. He cited certain episodes: The Fats, ready to burst, sitting down for the evening pig-out, while the Leans, doubled over by fasting, watch with envy from the street with their rail-thin faces, and next the Fats, at table, with overflowing cheeks, chasing away a Lean who had the audacity to enter humbly, one who resembles a candlepin in the middle of a population of bowling balls. It takes in the whole human drama; it ends up by classifying humanity into Lean and Fat, two hostile groups, the one devouring the other, to filli its stomach and enjoy. -- For certain he says, Cain was a Fat and Abel a Lean.
The idealistic socialism that Florent adopts is an indictment of the conspicuous consumption the Second Empire. And it is a theme that recurs in Zola. In La Curée, there is a remarkable scene of the piggishness of the noveaux-riches, who at a ball at the Saccard house, attack the buffet with stomach-turning piggery, so that even the servants are put off. As we will seine La Conquête de Palssans, the gluttony of the priest is seen as consuming the household, eating the protagonist and his family literally out of house and home. And in La Fortune des Rougon, it is Macquart's perpetual hunger that makes him resent the food on his own children;s plates as well as the (imagined) well-supplied table of the Rougons. His egotistical cries of revolution is nothing but the resentment of the Leans against the Fats is sen as a political issue.