If you ever think you're not in an "echo chamber", it's because you have internalized the ambient point of view as Truth.
It's a rather healthy thing I think for communities to maintain boundaries, and that includes ideological ones. When you enter into a community you must accept the responsibility of understanding that community not only from your current perspective but also on it's own terms. If you cannot reconcile this new point of view with your own then your simply in the wrong place.
Also, as anyone here should be able to tell you, it is not the goal of Lemmy to grow, it's goal is to exist. Growth as a goal is it's own ideology, and in any case Lemmy's ability to exist and grow in so far as it has is proof of the general correctness of it's ideals this far.
Without knowing your specific experience, I'll say incremental change might be easier. Start with cutting out only dark meat, it's the worst for you anyways. Opt for more meals including vegetables and such rather than focusing on cutting because that would be the space your moving into anyways so you'll need to get comfortable eating that way.