The vegan diet is exclusively plant-based. Dairy, meat, and fish are not consumed by vegans. While plants are a great source of fiber, antioxidants, carbohydrates, protein, fats, and minerals they are poor sources of Vitamin B12, iron, zinc, and omega 3 fatty acids.
A plant-based diet has smaller quantities of bioavailable iron when compared to meat, poultry, and fish eaters. Iron in heme form is better absorbed when compared to non-heme form iron. Plant-based food or non-heme iron absorption is inhibited by phytic acid present in these foods.
Zinc is one of the essential components of the six enzyme classes present in the body. The mineral helps transmit messages from one cell to the other. Zinc deficiency is a major public health concern.
Zinc deficiency can occur in people with diets low in bioavailable zinc food, like red meat and unrefined cereals rich in phytate and dietary fibers. Major manifestations of zinc deficiency include stunted growth and development, and an increased incidence of pregnancy complications (Gibson, 1994).
In US diets, more than half of Zinc comes from animal food. Vegetarian diets containing legumes, whole grains, nuts, and seeds, while do contain adequate quantities of zinc, the bioavailability is restricted due to phytic acid present in these foods. High levels of calcium can also reduce the bioavailability of zinc.
The risk of vitamin B12 deficiency in certain dietary groups, such as vegetarians, is well-recognized. Its deficiency can lead to a pernicious and fatal form of anemia. The common causes of Vitamin B 12 deficiency are atrophic gastritis, and Helicobacter pylori infection (this is common in developing countries of the world). Absolute vegetarianism for an extended period from 5 to 10 years can also lead to a deficiency in this vitamin. The vitamin is available only from foods of animal origin.
Plant-based sources of Omega3 are flaxseed, chia seeds, canola, walnut and soybean oils, leafy and green vegetables. These are short-chain omega 3 molecules that need to be converted in the body into long-chained fatty acids. Converting plant-based omega3 foods into a nutritionally useful form is an inefficient metabolic process. The absorption levels of this type of fatty acid are quite low.
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