My main concerns regarding vegan diets is the lack of creatine (and its potential effect on IQ) as well as children being raised as vegans (based on my minimal research, it seems that vegan kids tend to be shorter).

As someone who doesn’t eat meat at the moment, I’ve been debating eating meat again because 1) I don’t want it to negatively impact my intelligence/memory and then I make less progress on ai alignment 2) I’d be concerned it negatively impacts the growth (in all aspects) of my future children.

In general, I’ve been quite underwhelmed by the level of research (and written–up analysis) on the above concerns. It seems that lack of creatine does lower IQ, and I’d like more understanding as to whether the supplements actually work  to resolve that issue (or is absorption a problem?). That said, I’ve read that meat eaters typically only get about 1g/day of creatine and I supplement 5g/day (my guess is that beyond 3g you probably don’t get more IQ boost).

For children, I’m having a hard time imagining the quality of research will be sufficient by the time I have kids, so I will likely default to having them eat a mediterranean diet.

I think it's probably best to avoid listening to "celebrity doctors" and documentaries. This blog provides some good evidence based advice for vegan nutrition IMO:

https://www.scepticaldoctor.com/

Good article about protein here: https://www.scepticaldoctor.com/articles/protein-above-rda

I think the central point is that animals carry moral weight and that we should act accordingly, not that there are no trade-offs to to the health and pleasure of humans from abstaining from using animal products. It's not as if, given a scientific consensus that the optimal diet at our current tech level includes meat, animal advocates would cease advocating for abstaining from using animal products. Assigning animals a significant moral weight means that such very minor drawbacks to humans become a rounding error next to the major harms to animals.

Animal advocates who say that cutting out meat will not harm your health or will improve it, aren't presenting an unbiased argument about nutrition literature and human health. The conclusion is motivated by not wanting to hurt animals. Research that validates or debunks this motivated conclusion may be useful to animal advocates insofar as which vitamins and protein powders they might recommend, but it wouldn't sway the central point.

With regards to protein: studies consistently show getting enough protein to prevent sarcopenia or other diseases is not especially difficult, and in fact most people get substantially more than the recommended daily allowances. Also important is that consuming animal protein is positively correlated with all-cause mortality, while plant protein is negatively correlated. From what I can tell, though, this is probably because fiber is confounding the results.

Moving on from observational studies and to randomized controlled trials, it's unclear whether protein even has a meaningful effect on muscle strength, let alone something like lifespan, with some studies finding little or no effect from supplementation. It's really not clear protein would help with sarcopenia from the studies, but we'd honestly expect null results from theory alone. We know from surveys that the limiting factor in most people's muscle strength is physical activity, not protein. Most people get more than enough protein, and excess protein consumption turns into fat, not muscle. For most people, protein supplementation just can't help because they aren't moving enough.

The primary dietary determinants of health seem instead are mostly:

1. Polyunsaturated fatty acids (found in fish and vegetable oils)
2. Fiber (typically supplemented with psyllium husk)

I'm busy, so I'll stick to looking at the evidence base we've acquired just on fiber supplementation. Here's a bunch of insanely overpowered observational studies with sample sizes stretching into the hundreds of thousands, all showing reductions in all-cause mortality. Meta-analyses of RCTs? We've got those in spades.

There is a reason every doctor's dietary advice is exactly the same: "Replace refined with whole grains, avoid saturated fats and replace them with unsaturated fats." The reason is because we have million-person studies showing these interventions reduce heart disease. Note that heart disease is by far the leading cause of death among the elderly; sarcopenia doesn't really kill, although it does make life substantially worse. And importantly, both of these are substantially more common in plants than in animal foods, which offers a pretty good explanation for why vegetarians seem to live longer, even after controlling for confounders. And also for why vegetarian diets seem to improve health markers in RCTs.