Vitamin B12 is found naturally in animal foods such as meat, poultry, fish, eggs and dairy products. It is not present in plant foods with the exception of some algae. Because of this, vegetarians who do not eat any animal products are at risk of developing a vitamin B12 deficiency unless they supplement their diet or consume fortified foods. Vitamin B12 is essential for the proper function of the brain and nervous system as well as the formation of red blood cells. Symptoms of vitamin B12 deficiency include fatigue, weakness, constipation, loss of appetite and weight loss. In severe cases it can lead to anemia and neurological problems such as memory loss and depression.