In this section, we will deal with where vegans obtain essential nutrients and go further on controversial topics regarding veganism. Below is a list of the most common foods vegans use to obtain essential nutrients:
Good plant sources of calcium include tofu (if prepared using calcium sulphate contains more than four times the calcium of whole cow's milk), green leafy vegetables, seeds and nuts. The calcium in green vegetables which are not high in oxalate e.g. kale, is absorbed as well or better than the calcium from cow's milk. Some soya milks e.g. Provamel, Plamil, Granovita are fortified with calcium. Drinking hard water can provide 200mg of calcium daily but soft water contains almost none. Other calcium rich foods include black molasses, edible seaweeds, watercress, parsley and dried figs. Below is a list of common foods containing calcium:
The calcium intake of vegans tends to be slightly below the recommended optimal amounts but the body does adapt to lower intakes and there have been no reports of calcium deficiency in vegans. The fact that vegans have a slightly lower protein intake and exclude meat from their diet encourages their bodies to retain calcium so their dietary need may be lower than the typical omnivore. In fact, the excessive protein in cow's milk depletes the human skeleton of calcium and actually weakens bones. Cow's milk is the perfect food for calves, but it's not ideal for humans. Studies of the bones of vegans suggest that the likelihood of osteoporosis is no greater than for omnivores.Iron
Iron is a trace element which is needed by the body for the formation of blood. The human body normally contains 3-4g of iron, more than half of which is in the form of hemoglobin, the red pigment in blood. Hemoglobin transports oxygen from the lungs to the tissues. Iron is a constituent of a number of enzymes. The muscle protein myoglobin contains iron, as does the liver - an important source during the first six months of life. The body's iron balance varies mainly according to dietary intake, as losses from the body are generally small - although women lose iron during menstruation.
Vegans have a high dietary iron intake and although iron from plant sources is less well absorbed than that from meat, high levels of vitamin C in the diet enhances iron absorption. Studies show that the iron status of vegans is usually normal, and iron deficiency is no more common than in the general population.Vitamin B-12
The term B12 encompasses a group of related substances known as cobalamins. It is commonly but inaccurately believed that animal foods are the only source. In fact, active B12 is thought to be unique among vitamins in being made only by bacteria. The B12 found in meat (especially offal), eggs and dairy milk derives from the activity of bacteria living within the animals. Prolonged cooking, including boiling of cow's milk, destroys B12.
Deficiency is rare but may lead to abnormally enlarged red blood cells which characterize megaloblastic anemia. Vitamin B12 is also crucial for a healthy nervous system, and a chronic lack can eventually cause neurological symptoms.
Most cases of B12 deficiency occur in the general population and are due to a lack of intrinsic factor (a protein which is produced in the stomach and which ferries the B12 into the bloodstream), without which little of the vitamin can be absorbed. This type of deficiency leads to pernicious anemia; causes include small bowel disorders, the effects of some drugs, smoking and alcohol, gastric atrophy due to aging, and some parasitic infections. Pernicious anemia occurs in nearly 1% of the general population over the age of 60 years.
Despite the notoriety of this vitamin, dietary B12 deficiency in adult vegans is rare: some 15 cases have been recorded in the medical press worldwide since the 1980s. Not all cases will be published but it is significant that B12 deficiency is so uncommon that single case reports are still thought worthy of publication in medical journals.Vitamin D
Vitamin D is a fat-soluble vitamin which acts like a hormone, regulating the formation of bone and the absorption of calcium and phosphorus from the intestine. It helps to control the movement of calcium between bone and blood, and vice versa. In infancy and childhood, deficiency of vitamin D causes the deformed bones characteristic of rickets, while in adults a lack of the vitamin causes a softening of the bones known as osteomalacia. Deficiency is seen more often in northern countries, or where tradition dictates that the body is well covered by clothes, such as in parts of the Islamic world. An excess of the vitamin can cause loss of appetite, weight loss, nausea, headache, depression and deposits of calcium in the kidneys.
Adult vegans obtain adequate vitamin D if they regularly spend time outdoors in spring, summer and autumn. A dietary intake of the vitamin can be ensured by taking fortified products. In northern latitudes vegan women who are breast feeding should ensure their intake during winter by using fortified foods or taking supplements. Parents are advised to include vitamin D fortified foods or supplements if they wean their infants during the winter months, especially if they are dark skinned.Protein
Proteins are large molecules made from smaller units called amino acids. There are twenty amino acids commonly found in both plant and animal proteins. There are generally considered to be eight amino acids that the body cannot make itself which need to be obtained from the food we eat. These are isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. Infants additionally need food sources of histidine and possibly taurine. Proteins are necessary for maintaining tissues and for sustaining growth. They are also used to make hormones and other physiologically active substances.
Nutritionists once believed that plant proteins were of a poorer quality than animal proteins. Even now, plant proteins are sometimes called 'second class' proteins while animal proteins are elevated to the 'first class' department. This belief centered on early research on the poor laboratory rat which showed that giving extra amino acids of weanling rats reared on a plant-protein diet improved their growth. The same was assumed to be true for humans. However, the parameters of the experiments were set in such a way that differences in the quality of plant and animal proteins were exaggerated. Also, rats and humans have different nutritional requirements, since weanling rats grow at a much faster rate, relatively, than human infants and therefore need more protein. A comparison of rat and human milk makes the difference quite clear: protein comprises only 7% of the calorie content of human milk, while rat milk contains 20% protein. If weanling rats were fed only human milk, they would not thrive. These tests over-estimated the value of some animal proteins while under-estimating the value of some vegetable proteins and The World Health Organization has now abandoned this inadequate method of assessing the value of proteins to the human body.