Ultimately, animals must obtain vitamin B12 directly or indirectly from bacteria, and these bacteria could occupy a section of the gut which is posterior to the section where B12 is absorbed. Thus, herbivorous animals should either get B12 from micro-organisms in their rumens, or (if fermenting tree material in the hindgut) by reingestion of cecotrope fæces.
Supplement B12 is found in foods that come from animals, including fish and shellfish, meat (particularly liver), poultry, eggs, milk, and milk items. Eggs are typically discussed as a really good B12 source, however they also incorporate a factor that prevents absorption. However, the binding capacity of warmth treated egg yolks and egg whites is markedly reduced after warmth therapy. Particularly, insects such as termites incorporate B12 created by their gut micro-organisms, in a means analogous to ruminant animals. An NIH Fact Piece details an assortment of food sources of vitamin B12.
While lacto-ovo vegetarians generally get enough B12 by consuming dairy products, vegans will definitely lack B12 unless they consume B12-containing dietary supplements or B12-fortified foods. Instances of fortified foods include fortified breakfast cereals, fortified soy items, fortified energy bars, as well as fortified dietary yeast. According to the UK Vegan World, the present consensus is that any B12 present in plant foods is very likely to be unavailable to humans because B12 analogs can compete with B12 and inhibit metabolism.
Claimed sources of B12 that have actually been shown to be inadequate or unreliable with direct researches 60 of vegans include laver (a seaweed), barley grass, and mortal intestinal bacteria (mortal colonic micro-organisms create B12, but it can not be soaked up from the colon).