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Originally written by FatBatMonkey:

Actually, various studies have shown that various trace minerals and chemicals that keep the body fit and healthy can only be found in meat. Also these things were not naturally occuring, being by-products of some process or something (don't ask me what, I don't know anything about biology).

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As for organic compounds that are only found in animals, I'd be very surprised if you could name even one that's been found to be necessary to human health and can't be made in the human body from compounds found in plants.

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Vitamin B-12

Sources of vitamin B-12 that are not derived from animals include B-12 fortified foods (such as some brands of soymilk, breakfast cereals, and nutritional yeast) or supplements (see Table). Unless fortified, no plant food contains significant amounts of active vitamin B-12. Foods such as sea vegetables and spirulina may contain vitamin B-12 analogs; neither these nor fermented soy products can be counted on as reliable sources of active vitamin B-12 (29,88). Lacto-ovo-vegetarians can get adequate vitamin B-12 from dairy foods and eggs if these foods are consumed regularly.

Vegetarian diets are typically high in folic acid, which can mask the hematological symptoms of vitamin B-12 deficiency. Therefore, some cases of deficiency may not be detected until after the onset of neurological symptoms (89). If there are concerns about vitamin B-12 status, serum homocysteine, methylmalonic acid, and holotranscobalamin II should be measured (90).

A regular source of vitamin B-12 is crucial for pregnant and lactating women and for breastfed infants if the mother's diet is not supplemented. Infants born to vegan mothers whose diets lack reliable sources of this vitamin are at especially high risk of deficiency. Maternal vitamin B-12 intake and absorption during pregnancy appear to have a more important influence on vitamin B-12 status of the infant than do maternal vitamin B-12 stores (91). Because 10% to 30% of those over the age of 50 years, regardless of the type of diet they follow, lose their ability to digest the protein-bound form of the vitamin that is present in eggs, dairy, and other animal products, all people over the age of 50 should use vitamin B-12 supplements or fortified foods (92).

Studies indicate that some vegans and other vegetarians do not regularly consume reliable sources of vitamin B-12 and that this is reflected in less than adequate vitamin B-12 status (27,29,88,89,93-95). It is essential that all vegetarians use a supplement, fortified food, dairy products, or eggs to meet recommended intakes of vitamin B-12 (see Table).

Absorption is most efficient when small amounts of vitamin B-12 are consumed at frequent intervals. This could be achieved through use of fortified foods. When less than 5 µg of crystalline vitamin B-12 is consumed at one time, approximately 60% is absorbed, whereas 1% of a dose of 500 µg or higher of vitamin B-12 is absorbed (92).

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