We recently bought dinner for two of our best friends. Let's call them "Bill" and "Mary". The food at the restaurant was excellent, but Bill left a little on his plate. Mary, Barbara, and I did everything short of picking up the plates and licking them. We used some of the excellent bread to mop up the last drops of superb sauce.
Later, Mary told me that Bill had been brought up in the US always to leave some food on the plate. She had given up trying to change that.
I told Mary that I had heard an expression "leave something on your plate for Lady Manners" when I lived in England. The justification (if you can call it that) given to me was that if you ate everything on the plate, the hostess might feel that she had not fed you enough. I told Mary that I thought that this was ridiculous, and she agreed.
An omnivore, I have always been a member of the "clean plate league", which sometimes causes some dismay to Barbara - not because I want to eat everything, but because I am so slow about eating such food as cracked crab.
Those of us who lived in the UK during WW II knew that it was unpatriotic to waste food. German submarines sank many ships bringing food to the British Isles. Many hundreds of merchant seamen lost their lives as a result.
Americans waste a lot of food. I was incensed at a recent question in a survey, asking which of the following leftover foods from a holiday meal did we throw away: Turkey, Dressing, Mashed Potatoes, Pumpkin, or Cranberry Sauce? There was no option for "None of the above".
We don't throw food away at our house. Leftovers are refrigerated and eaten within a few days.
WW II is long over, but I still consider wasting food to be sinful.