I was more referring to the defficiency resulting in poorer mental health outcomes, less so than the well understood nutritional defficiencies.

https://www.tandfonline.com/doi/full/10.1080/10408398.2021.1974336#abstract

Nutrition is a very complex topic and like with most things health related, we dont understand the full picture yet, and each person is slightly different. Some people might do we well abstaining from meat, others would not.

I think the main message is that sustainability is a goal we should all strive for, but diet is a balance and not a religion. With moderation animal products may be neccesary and sustainable

The sustainability picture will also differ greatly based on where you live. Meat may be impractical in your region due to factory farming and poor environmental regulations.

Some eggs, milk or cheese from a real free range local farm might do better on the sustainability picture, than imported soy beans grown overseas on burned forests.

We buy some mutton on occasion from a local solar power farm who keeps sheep to eat the grass that grows below the solar panels, rather than having to get commercial lawn mowers in. They have even partnered with the local veterinary school help with the health monitoring of the animals.