If you want to turbo optimize your life and give up caffeine so your body can absorb non-heme iron be my guest. It’s far simpler to eat as omnivores as humans were meant to be, especially with so many factors on the scale against your favor.
Humans weren't "meant" to eat any single way, for what it's worth. We have the good fortune of possessing exceptionally flexible diets, but we can survive readily on many variations of what's possible.
Something people frequently overlook (or are unaware of) is that in much of the world, animal agriculture utilizes B12 supplementation. This is part of why there is B12 in commercial animal products. Without that, B12 levels in commercial animal products would be lower. Further, people who eat animal products aren't guaranteed to avoid deficiencies.
The idea that we "need" meat is thoroughly debunked by decades of excellent, high-quality research. What we "need" as far as B12 goes is essentially less sanitary environments; we (and animals we ate) used to get enough from food and water which wasn't clean by current standards.
For me it makes no difference whether I consume animal products or not. I’ve consumed no animal products in about five months now, and aside from needing to spend a bit longer looking at labels when I first started, now I know what I’m doing I spend no more or less time on food.
I take a big multivitamin in the evening and that’s it.
