I want to preface this with the fact that I never said you can't have a well-balanced vegetarian or vegan diet, because I feel like that's what you're thinking I'm implying.

> Common nutrients that even non-vegetarians do not generally get from meat.

Other than Vitamin D3, meat is objectively an excellent source of all of those nutrients. Fish is an excellent source of iodine and omega-3, and saying people do not get zinc, iron, or calcium from meat is just incorrect.

> These are all things that non-vegetarians get in sufficient quantity from non-meat sources. So why would someone becoming a vegetarian suddenly stop eating these things.

Maybe because they never started eating those to begin with? I do not know, and I can only speculate on the different reasons. Each person is different, but all we know is that it does happen[1]. Some people just don't have those in their diet.

Anecdotally, I don't think I ever ate beans until I was in my early 20s because my parents just never cooked with them. We also pretty much only had sea salt available, and most of our food was cooked with butter instead of vegetable oil. We weren't unhealthy, but if I immediately dropped meat from my diet at that time without changing anything else, I would have started to have issues.

> While i agree in general, your definition of "careless" is so ridiculous that I think meat eaters would rapidly be in trouble if they were this level of careless.

I'm not going to argue semantics. My argument is about the statistics and how these dietary studies tend to fail to account for extremes in behavior. Vegans, vegetarians, and pescetarians are just less likely to have these extremes.

To reiterate the results from the previous study I linked[2], semi-vegetarians (people who only occasionally had meat) have a fairly worse mortality rate than vegetarians, yet strictly speaking their diet only varies by having meat once or twice a month. The only way this makes sense in my mind is either there's a huge behavior difference in these two groups (less care put into their diet), or that meat is so incredibly unhealthy that just eating it occasionally will knock years off your lifespan. Considering the standard deviation of those results are larger for both non-vegetarians and semi-vegetarians (and that pescetarians have a significantly lower mortality rate than even the vegan group), I would bet on the former.

And if you don't think there's a lot of people that are completely careless about their diets, just remember how much soda the average American drinks in a single day[3], despite half of the population not drinking soda at all. And nearly a quarter of Europeans don't get regular checkups at a doctor[4], despite their access to healthcare. It's safe to say that a lot of people that just flat out don't care if they have a balanced diet (or exercise, regular healthcare, etc), and when you don't care you tend to eat meat.

When we get health studies that don't take this into account, we end up with fad diets because those studies essentially just show that those who pay attention to their diet tend to be healthier. To demonstrate the issues with those studies, this one[5] concludes a meat-only diet has very good health benefits compared to the general population.

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8746448/

[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4191896/

[3] https://news.gallup.com/poll/156116/nearly-half-americans-dr...

[4] https://ec.europa.eu/eurostat/web/products-eurostat-news/-/D...

[5] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8684475/