[virtuallynathan]

Yes - vitamin B12 isn’t found in plants. Other minerals are also harder to come by, like Zinc and Iron. The bio-available form of Omega-3 Fatty acids, EPA, DHA, and DPA are also only in animal products. Long-term veganism without health consequences isn’t possible without careful supplementation. If you eat fish and eggs, you are mostly covered, although I recall studies showing vegetarians had lower levels of B12 and other vitamins/minerals vs their omnivorous counterparts.

You can get all vitamins/minerals needed by just eating animal products, if you so desire. Plants don’t contain anything essential for human health, so far as we can tell today.

[yissp]

Worth noting that there are a wide variety of B12-fortified plant-based foods available (non-dairy milks, cereals, etc.). One can also find algae-based EPA + DHA supplements.

[virtuallynathan]

Yes, this is true, although I don’t believe these tend to be very healthy foods. Algal Omega3’s are a good source (although technically not a plant).

[loudtieblahblah]

Collagen is really low for vegetarians which, I don't know about health consequences, but doing without it for long enough makes you look sickly.

[lrnStats]

This is not relevant to the question asked since it's about vegetarians who gave eggs and milk.