Thank you for your lengthy answer, which adds and makes me brush up on my current knowledge. Still, we're merely skimming the surface here, as everything is interconnected and there's too much knowledge available to handle and weigh everything.

You're right that population is the main cause of humans causing trouble on a planetary scale. 95-97% of land-based mammals are either humans or cattle, according to current estimates. Nature is then left with the small percentage of mammals left as part of a viable natural ecosystem. The strain on it is not difficult to see. Still, the current global population can be sustained by our planet provided we move away from eating meat, as approx. 75-80% of the global agricultural area is used for cattle. Including dairy, that is.

The carbon that plants use comes mainly from the air, not from the soil, through CO2. Permaculture is an improvement compared to common agricultural monoculture, but mainly relies on cattle to resupply the minerals in the soil, human waste is generally no part of the intended circularity. It used to be, some centuries ago, before sewers became commonplace. Presently it's more difficult and therefore costly to regain all those minerals among all the toxins in sewage systems, so we don't. We just have fertilizer factories on one end of the system and flush it down the toilet on the other end. Problem with that is that it heats up the atmosphere. (Solutions for this still to be worked out.)

I don't get the statement on animal wellbeing and them being raised in the same area. Is that about family bonds between animals? Anyway, how people treat animals in the agricultural industry is not so pretty, the more knowledge I gain on that over the years, the worse it gets. Animals are just used for human pleasure, either on our plates or as pets. I've reached a point where it would be best when animals are not kept at all by humans. Only have wild animals to live their lives however they see fit, with as little human intervention as possible. I know it's quite a radical stance that I will not witness in my lifetime, but it is still a point on the horizon to aim for. At least there's still some nature left where this is true, quite often even in urban areas, where wild animals freely roam their environment, surviving on whatever they come across.

Health is quite a topic altogether, meat eating is correlated not only with certain types of cancer but also with coronary and vascular problems. The study you refer to is but one and deals mainly with replacing saturated fats with omega-6 types, I've understood that it's more about the ratio between omega 6 to omega 3 in our diets. These can come from fish oil, but then includes heavy elements and microplastics that fish filter out from whatever's floating around in the oceans. Vegetable oils can also be used for cholesterol management, e.g. rapeseed oil seems to have a good balance in fatty acids. But health is of course also affected by caloric intake, exercise, minerals, sugars and other carbohydrates, etc. All recommended levels can be met without the use of meat. There was even a study on fish having health benefits, not because fish are so healthy, but they replace meat, which is unhealthy. See e.g. https://www.everydayhealth.com/diet-nutrition/we-should-be-eating-more-tasty-little-forage-fish-study-finds/

Thanks for your recommendation on vitamin A, I'll keep an eye open for that. :o)

And I'm quite happy, despite all the problems we're having and facing up ahead. It seems that whenever humans need to choose between good and bad, we generally tend to choose the bad, time and time again. Still, this doesn't affect my appreciation of life too much. It remains a great gift to be alive in this universe, as far as we can see.

I hope you can find happiness as well, wherever you may go.