Originally Posted by Alan K

Craving A-1 steak sauce aside, the nutritional value of meat and tofu are drastically different. So one can’t very well add A-1 to their veggie loaf and assume that they are going be fine in the long run. This is why vegans end up with certain deficiencies, such as Vitamin B12, which for most omnivores is abundantly present in their diets (meat and fish). If they pursue vegan life-style for about a year without using chemically synthesized (many of them are also philosophically against “better living through chemistry”) vitamins etc, signs of deficiencies become overtly visible.