Just read a recent article in the New Scientist about choline. (Choline is a necessary nutrient for humans and many other animals)

Basically the message is without it in your diet it can coat you liver in a fatty layer which, depending on your genetics/lifestyle, can be a long term life risk.

Easily consumed from meat, rarely and poorly found in vegetable fodder. The human body can make some, but not sufficiently, again down to variations in genetics.

Like vitamin B₁₂ - vegans should be aware of the gamble. "Not many people will succumb" is small comfort for the few who have wrong genes that science haven't identified yet.

Happy Holiday everyone!