Learn English – What’s the meaning of “When the pig has had a belly full, it upsets the trough”

I'm not sure about the very origin of the saying and I'm inclined to think it's probably lost for ever.

What I can confirm though are the following points:

• Yes the Old English word for apple ("æppel") was a generic term for any kind of fruit. Just as the ancestor of deer (deor) meant any kind of wild animal (see German "Das Tier").

• This is not a phenomenon limited to English but is already true for instance in Greek where μῆλον pronounced "melon" was a generic term for any kind of fruit growing on trees. For instance μηλοπέπων ("melopepon" ripe fruit => melon), μῆλον Αρμενιακόν ("melon armeniakon": Armenian fruit => apricot), μῆλον Κυδώνιον ("melon kudonion": fruit from Cydonia => quince), μῆλον Μηδικόν ("melon medikon": fruit from Media/Assyria => citrus), μῆλον Περσικόν: fruit from Persia => persica => pesca => pêche => peach) and so on.

• There are even traces of this in Italian:

  • Since mela enters in the name of melo cotogno (the quince) even though it is abbreviated to cotogno. Allowing for a certain amount of confusion this is also the probable origin of the Spanish word melocoton (a kind of peach). The origin of "cotugno" being the city of Cydonia (Κυδωνία) a town on the Northern coast of Crete, believed to have been the origin of this fruit.
  • Another Italian fruit name containing mela is the melanzana (aubergine from melo-badingian - باذنجان "badingian" is the Arabic for the eggplant/aubergine and the etymology of the word aubergine itself).
  • Yet another Italian fruit name is melograno which means pomegranate (from Latin pomum "apple" granatus "seed" or French pomme-grenade from Granada in Spain).
  • As noted in Sklivvz's comment below, the word melone itself is formed from *melo* suffixed with the standard Italian augmentative "-one".

As for the association of the apple with a good health one can also cite:

• The Spanish saying "Sano como una manzana" (healthy as an apple).

• The etymology of pomade which started as a French word for topical/ointment made from apple (pomme in French) and fat. See also the Italian pomata.

A few references for proverbs

• The Oxford Dictionary of Proverbs,
• Wikipedia,
• Wikiquote,
• phrases.org.uk.

In the UK there's "You don’t get owt for nowt." (owt = ought = anything/something, and nowt = nought = nothing).

Also Look out for number one, often followed by If you don't, no one else will., which effectively expresses the same sentiment.

Plus, as Wayfaring Stranger comments, There ain't no such thing as a free lunch.