The only nutrient that humans need that cannot be found naturally in plant foods is vitamin B12.
Actually, neither plants nor animals synthesize vitamin B12: only bacteria make the biologically active form. Animal tissues can store the B12 made by the bacteria, which can then be passed along to carnivores when they eat animal tissue. Ruminants (cows, goats, sheep, giraffes, llamas, buffalo, and deer) have bacteria in their rumens (stomachs) that synthesize vitamin B12, which is then passed down and absorbed by their small intestines. Large carnivores get their B12 from eating these grazers.
Your digestive tract also contains B12-synthesizing bacteria, which is one reason that vitamin B12 deficiency disease is rare in humans, even among vegans. Most of the bacteria is in your colon, and B12 is absorbed "upstream" in the ileum, so you don't absorb the B12 that's made in your colon unless it somehow gets back into your upper digestive tract. Feces contain large amounts of active B12. Our ancestors lived in close contact with each other and their farm animals, and they got their B12 by eating unsanitized food. We now live in over-sanitized conditions, and the need for B12 supplementation for vegans is the result of our obsession with cleanliness.
If you were raised on an omnivorous diet, you probably have about 2 to 5 milligrams of B12 stored, mostly in your liver. That's at least a three-year reserve. Your body can conserve this supply by reabsorbing B12 from your bile, making your reserves last an average of 20 to 30 years after becoming a strict vegan if you consume no B12. In reality, you do get small amounts of B12 from your intestinal bacteria, unwashed vegetables, and the environment.
When you consume vitamin B12, hydrochloric acid in your stomach separates it from any protein to which it may be attached. Then, vitamin B12 combines with a protein made by your stomach called intrinsic factor and is absorbed by your body. Some people have pernicious anemia, a condition where they cannot make intrinsic factor. As a result, they have trouble absorbing vitamin B12 from food and supplements.
The amount of vitamin B12 you need each day depends on your age. For most adults, it's 2.4 micrograms (mcg).
Nori, the dried sea vegetable used to make sushi, has substantial amounts of active vitamin B12, which it obtains from symbiotic bacteria that live on it. Some breakfast cereals, nutritional yeasts, and other food products that are fortified with vitamin B12. To find out if vitamin B12 has been added to a food product, check the product labels.
Vitamin B12 is also found in almost all multivitamins. Check the Supplement Facts label to determine the amount of vitamin B12 provided.
Many people other than vegans may not get enough vitamin B12 or have trouble absorbing it:
Lack in iron and b vitamins
It is hard to get protein
Not all vegetarians eat gelatine, but as an ovo-lacto vegetarian, I find no problem with its taste or texture.
It goes into our waterways.
It isn't really a problem, but vegetarians have be careful to get enough vitamin B12; this comes mainly from meat, dairy and eggs so vegetarians who eat dairy and eggs shouldn't have a problem. Vegans, who don't eat dairy or eggs may take supplements although many prepared vegan meals contain extra B12.
Traditionally, vegetarians have to watch their intake of B12 which comes from meat and fish, but it also comes from milk and eggs. In practise, vegetarians in the West - where people chose to be vegetarians - are very aware of what they are eating so vitamins aren't a problem.
what nutrients commonly present a problem in the diets of vegans
yes, colombia has a particularly servere problem with terrorism.
human suffering and death
if not treated properly the dog could have possible hearing loss or hearing deficiencies in the future
Seems a real neurological problem, but have you ever tried with vitamins especially Vitamin B12? Or ever considered the vitamin deficiencies?
A nutrient pollution is one of the most widespread, challenging and costly environmental problem in the United States of America today. Too much phosphorous and nitrogen in the water and air is the cause of this dilemma.
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It is not particularly important.