What do the citizens of the Metro eat?

After the nuclear apocalypse the surviving citizens of Moscow fled to metro stations throughout the city to endure the radioactive fallout. The Metro franchise takes place 20 years after Armageddon, surely there isn't enough food preserved to sustain the entire metro population.

Before fleeing Moscow during the events of Metro Exodus, how did those living underground sustain themselves? Are farms maintained underground, without sunlight? Does hunting or scavenging the Moscow ruins provide enough food for everyone? Could food be brought in externally, even with the Moscow military blockading the city?

Solution 1:

The most common food sources are:

• pigs;
• chicken;
• mushrooms;
• rats (sometimes mutated rats).

Vegetables are more rare, as they can only be grown in hydroponic greenhouses.

Animals are kept on farms:

Some of the known pig farms in the Moscow Metro include: Rechnoy Vokzal of the anarchists, as well as Sokol, Aeroport, Dinamo and Belorusskaya stations of the trade outpost.

How it looks like in Metro 2033 game (sign on the wall says "Farm" in Russian):

Sources: Metro world overview , Pigs (yes, they have separate wiki page for pigs).

From what I remember from reading books, animals were originally taken from Exhibition complex - VDNKH which is located atop of one of metro stations (also called VDNKH). Amongst other things this complex contains Agricultural Exhibition, hence animals.