"Avoiding meat and dairy products is the single biggest way to reduce your environmental impact on the planet, according to the scientists behind the most comprehensive analysis to date" https://www.theguardian.com/environment/2018/may/31/avoiding-meat-and-dairy-is-single-biggest-way-to-reduce-your-impact-on-earth
I've developed lactose intolerance in adulthood, so dairy is already out. I bet I can excise mammal from my diet if I actually get organized about it.