There are people who have tried to investigate this thoroughly. My understanding is that there is a direct correlation between your actions an the supply.
> "If someone gives up 1 lb of chicken, total consumption falls by 0.76lb in expectation."
The mechanism is simple: if the stores are 100% responsive to your demand, your purchase directly affects supply. If they are not 100% perfect, they still have a mechanism through which they buy in bulk. So, roughly speaking, you might have a 1% chance of triggering a batch order for an extra 100 lbs when you purchase 1 lb of meat. And the same goes up the supply chain.
> "If someone gives up 1 lb of chicken, total consumption falls by 0.76lb in expectation."
https://forum.effectivealtruism.org/posts/fZp6Fpowmd5a8Lu2w/...
Directly: https://reducing-suffering.org/comments-on-compassion-by-the...
The mechanism is simple: if the stores are 100% responsive to your demand, your purchase directly affects supply. If they are not 100% perfect, they still have a mechanism through which they buy in bulk. So, roughly speaking, you might have a 1% chance of triggering a batch order for an extra 100 lbs when you purchase 1 lb of meat. And the same goes up the supply chain.