Please let's not resort to "appeal to nature", because that can certainly be abused both ways (and frequently is). There are certainly all sorts of sketchy vegetarian and vegan bogus arguments about why not eating animals is natural (and certainly eating dairy and chicken eggs isn't natural).

We weren't built for anything, and just because something is natural, doesn't mean that it's good or right. If we ruled our lives by what was natural, we'd die in our thirties, have high infant mortality, and while we would eat meat, we would also chase after it with sharpened sticks, and more of us would die from starvation. Agriculture is unnatural; it's technology. Yes, our ancestors ate meat, but that alone doesn't mean that we need to. The OP's system couldn't handle her vegan diet, so she needs meat, but that doesn't mean everyone needs meat.

If you want to eat meat, eat meat. That's reason enough. If you find that you personally physically need to eat meat, then please eat meat. But neither the omnivore nor the vegan who claims that one diet is universally nutritionally or morally optimal in virtue of being natural is making a solid justification.