Volume is pretty rigorously tracked by regulatory bodies that are responsible for food safety.
The US’s data is here: https://www.ers.usda.gov/data-products/livestock-and-meat-domestic-data/
I’d copy and paste some stuff into this thread, but it looks like some parts of this site are under maintenance right now. That said, others have charted the data. https://www.agweb.com/opinion/drivers-us-capita-meat-consumption-over-last-century
Any idea what caused the dip from 04 to 09?
That’s actually quite an insane chart. So the average american eats around 125kg of meat a year? France is at 83kg, Italy at 81kg and Canada at 82kg.
https://en.wikipedia.org/wiki/List_of_countries_by_meat_consumption
Current german recommendations for healthy eating are saying that around 300 grams of meat a week are the max and Americans really seem to eat that every day.
I’m not working in the meat industry, but in the german food industry. German meat consumption has gone significantly down, but the most “feelable” effect would be that vegan and/or vegetarian options are now a must for every restaurant owner who knows what he is doing. A few years ago it was normal for restaurants to have no vegan option on the menu or for them to be kind of crappy. Now there are so many vegetarians that you will run into problems with your restaurant if your vegetarian option is crappy - because those vegetarians will complain to their family and friends and lead them into other restaurants.
(and yeah, there are still restaurants left without good options for vegetarians. Your region also might play a role - but chances are that you can find a pizza without meat on the menu that is not a Margherita)