The vegan diet has gained momentum in recent years, with more people transitioning to the diet, whether for health or more ethical-based reasons. It’s often characterized as very restrictive, is associated with health benefits but also raises concerns. Controversy regarding the diet exists within the public sphere, with those actively supporting and advocating for it, and others questioning its purpose and proposed benefits, perhaps because of a lack of knowledge about the diet.
The vegan diet is defined as one that includes only plant foods, namely, grains, vegetables, fruits, legumes, nuts, seeds, and vegetable fats. It is described as a restrictive diet as it excludes meat, fish, and its products which are abundant sources of protein, essential vitamins, and minerals.
Nutrients of particular concern in a vegan diet include protein, calcium, vitamin D, vitamin B-12, riboflavin, zinc, iron, fiber, as well as fat and essential fatty acids.
Protein – Dietary protein sources in the vegan diet are plant-based proteins. Interestingly, on a global basis, plants provide about 65% of the world’s supply of edible protein. Such products include soymilk, tofu, tempeh, seitan, legumes, grains, nuts, and seeds. But, the dietary protein from plant foods is only about 85% digestible. To counter the effects of the lower digestibility of plant proteins, the Recommended Dietary Allowances (RDA) suggests increasing daily recommendations for vegans by 10 to 15%.
Calcium – Vegans can easily meet their daily requirements without supplementation through the consumption of both vegetables and calcium-fortified non-dairy milk. Non-dairy milk/yogurt averages 200-300 mg/cup while cooking green leafy vegetables increases the calcium bioavailability from anywhere between 30-70 mg/cup to 200-350 mg/cup depending on the green (collard leaves – 2350 mg/cup, turnip greens 250 mg/cup. However, if vegan diets are unvaried, especially in children, it is advisable to consume calcium supplements between meals under guidance.
Vitamin D - Vitamin D, an essential nutrient, is both produced in the body by sunlight exposure and found in smaller quantities within foods. However, vitamin D is limited in non-fortified foods, with the best sources being fortified products, in particular, fortified dairy milk. For vegans, vitamin D fortified foods include soymilk, rice milk, and breakfast cereal. On average, adequate vitamin D is obtained both by sun exposure and consumption of fortified foods in both vegans and in non-vegans.
Vitamin B-12 – Vitamin B-12 is mostly obtained in animal-derived food; it is often classified as a nutrient that both vegetarians and vegans lack. However, this issue should not be of concern if eating a varied diet of fortified foods. Similar to vitamin D, the best source of vitamin B-12 is fortified food. Adequate vitamin B-12 can be achieved by consuming fortified foods such as breakfast cereals, soy beverages, nutritional yeast, and meat analogs. Those that are unfortified are unreliable sources.
Zinc – Zinc, an essential mineral, is found in similar densities in vegan, omnivorous, and vegetarian diets. Yet, certain concern exists due to the reduced bioavailability of zinc in plant sources. While vegans consume zinc via legumes, whole grains, wheat germ, fortified cereals, nuts, and tofu, the bioavailability of zinc from plant foods is reduced by phytate in whole grains and legumes. Phytate, bind with minerals, preventing mineral (zinc) absorption.
It’s evident that vegetarians have lower levels of total zinc and plasma zinc concentrations, although most often in acceptable ranges. This is due to lower zinc intake and absorption. However, it is observed that over time, there is an adaptation by decreased zinc excretion when dietary zinc is low.
Iron – Iron consumption is often a concern in vegetarian and vegan diets. The two different forms of dietary iron, are heme and non-heme. While non-heme iron is found in plant foods, heme iron is only found in animal foods that originally contained hemoglobin, and in general absorption of non-heme iron is lower than heme iron.
Although on average, iron intake appears at or above the RDA recommended daily levels, due to the lower absorbability of non-heme iron, vegetarians have lower iron stores. A higher percentage of individuals have stores below the normal range. It’s well known that low levels of iron cause iron deficiency anemia. But the studies have stated that “Vegans/vegetarians have no higher rates of anemia than those seen, in the general population.” This could be because, absorption of non-heme iron is greatly enhanced by vitamin C and other organic acids found in vegetables and fruits, both significant components of vegetarian and vegan diets.
However, lower levels of iron are detected in vegans, which may be explained by the composition of the vegan diet. Once again, increased levels of phytates in vegan diets decrease the absorption of minerals, such as iron. Studies have suggested adaptive regulatory response in vegans which allows for increased absorption of iron. That is, for vegans, ascorbic acid and other dietary factors can promote iron absorption even in the presence of phytates, increasing the once lower levels of iron in vegetarians and vegans.
Fiber – Fiber is a necessary part of every diet. Dietary fiber is a type of indigestible carbohydrate and is either soluble or insoluble. While soluble fiber attracts water and slows digestion, insoluble fiber helps food to pass more quickly through the digestive system from the stomach into the intestines. Studies have shown fiber intake to be higher in vegans in comparison to omnivores and vegetarians, even exceeding daily recommendations. High fiber intake is generally believed to result in more favorable lipid profiles and lower triglyceride levels.
Fat and essential fatty acids
It’s ideal to obtain about 25 – 30% of energy in the regular diet from fat, including both fats and essential fatty acids. Here, the particular concern is long-chain omega-3 fatty acids, namely docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). While vegan diet fats rely on nuts, seeds, avocado, soy products, and vegetables to meet their energy and nutrient needs, they lack in DHA and EPA. While the linolenic acid found in seeds can be converted to EPA and DHA, its efficiency of conversion is reduced in diets high in the omega-6 fatty acid linoleic acid, of which vegan diets seem to have a high amount.
Thus intake of essential fatty acids should be taken into greater consideration in the vegan diet, as they are essential to cardiovascular health, and brain and eye functions. Lowering the amount of omega-6 fatty acid, linoleic acid, will increase the efficiency of conversion of linolenic acid to both DHA and EPA
Currently, there are no known risks for diets low in long-chain omega-3 fatty acids, although an increase in such to obtain a more desirable ratio of omega-6 to omega-3 fatty acids is beneficial.
Overall, the key to a nutritionally sound vegan diet is variety. A healthy and varied vegan diet includes fruits, vegetables, plenty of leafy greens, whole grain products, nuts, seeds, and legumes in the right proportion and portion. Nutrients intake discussed above, are the specific nutrients of concern in vegan diets. Greater attention to the intake of these nutrients should be given, therefore guidance of a certified nutritionist is needed to understand where your diet might be lacking, and how to overcome it in the right way. Well-Planned vegan diets are regarded as appropriate for all stages of life, including infancy and pregnancy,
Vegan diets have been shown to lower the risk of type 2 diabetes, high blood pressure, obesity, and ischemic heart disease. It tends to be lower in some micronutrients thus, as, with a poorly-planned diet of any other variation, an unbalanced vegan diet may lead to nutritional deficiencies that nullify any beneficial effects and may cause serious health issues.
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