Vegetarian and Vegan Diets – What Are the Potential Deficits?
Vegetarian and vegan diets come under much scrutiny and disparagement from omnivores, even though much evidence points towards vegans being healthier than omnivores, so are there really any nutritional deficits in those diets and of so what are they?
Carbohydrates
Vegetarian and vegan diets are proportionately rich in fruits and vegetables, which are nutrient dense. However, compared to omnivorous diets, they diets are also contrastingly dense in grains and legumes, which are sparse in nutrients per gram compared to fruits and vegetables, and are dense in anti-nutrients like phytates, meaning that food is not digested easily.
Vitamin B12
Deficiencies in vitamin B12 are frequent in vegetarians and vegans. Vegetarians and vegans are significantly more likely to experience vitamin B12 deficiencies compared to omnivores. Vitamin B12 works synergistically with folic acid in the synthesis of DNA and erythrocytes. It is also critical to neural function. Consequently B12 deficiency can lead to several physiological problems including: lethargy; fatigue; anaemia; physical weakness; memory loss; fluid intelligence; visuospatial ability; psychological problems; neurological problems; and several more.
A frequent fallacy believed, is that plant sources such as soy, spirulina, brewer’s yeast or kale etc. may provide sufficient vitamin B12. However plant sources also contain cobamides, analogues of vitamin B12, which prevent its absorption and increase the necessity for its consumption.
Calcium
Theoretically the calcium consumption of vegetarians is similar to that of omnivores, given that both consume dairy products. However it is significantly lower in vegans, whose diets are generally deficient in calcium. Whilst leafy greens often contain high calcium contents, it is not digested effectively or efficiently owing to the presence of anti-nutrients such as phytates and oxylates which inhibit calcium absorption and therefore the quantity of calcium which can be absorbed by foods. Moreover, it would require several servings of leafy greens to match the same calcium levels as a single serving of milk or cheese.
Iron
Whilst the consumption of iron is similar in vegetarians and vegans compared to omnivores, the bioavailability of iron in plant foods is lower than that in animal foods. The absorption of plant based iron sources are inhibited by commonly consumed foods such as coffee, tea and dairy products and supplements such as fibre and calcium, which explains why vegetarians and vegans have lower iron levels than omnivores, and why vegetarian and vegan diets reduce non-heme iron absorption and total iron absorption.
Zinc
Whilst zinc deficiency is uncommon in western vegetarian and vegan diets, their consumption falls below recommended intake. Moreover the absorption of zinc from plant foods is also compromised by phytates and the vegetarian and vegan diets tend to reduce zinc absorption compared to omnivorous diets, meaning that even when vegetarians and vegans exceed daily recommended intake, they still may experience mineral deficiencies.
EPA and DHA
Whilst plant foods contain the essential fatty acids linoleic acid (omega-6) and alpha-linolenic acid (omega-3), the benefits of the long-chain omega-3 fatty acids EPA & DHA have been increasingly highlighted. These fatty acids are preventative of or therapeutic to a wide range of diseases including some cancers, asthma, depression, cardiovascular disease, ADHD, and autoimmune diseases, such as rheumatoid arthritis.
Some alpha-linolenic acids may be converted from plant foods into EPA & DHA. However this conversion is poor in humans. Vegetarians and vegans specifically have significantly lower levels of EPA & DHA than omnivores. Moreover, the conversion of ALA to DHA depends on zinc, iron and pyridoxine, which are nutrients for which sufficient consumption is far less likely for vegetarians and vegans compared to omnivores.
Vitamins: A and D
Vegetarian and vegan diets, nearly lack two of the fat-soluble vitamins entirely vitamins A and D. Vitamin A promotes healthy immune function, fertility, eyesight and skin. Vitamin D regulates calcium metabolism, regulates immune function, reduces inflammation and protects against some forms of cancer.
These important fat-soluble vitamins are largely concentrated, and sometimes almost exclusively found in animal foods such as seafood, organ meats, eggs and dairy products. Whilst some little-known mushroom species can provide large amounts of vitamin D, they are rarely consumed and often difficult to find. Consequently vitamin D levels are much lower in vegetarians and vegans compared to omnivores.
There is a common misconception that plant foods contain vitamin A. Plants contain beta-carotene, which is the precursor to active vitamin A (retinol). Whilst beta-carotene is converted into vitamin A in humans, this conversion is inefficient, and it is extremely difficult to consume vitamin A from plant foods without fortified juices or taking supplements.
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Summary
From an evolutionary perspective, is very difficult to maintain any diet, which contains scarce quantities of nutrients which are critical to human function. Common sense dictates that nutritional needs are met through the consumption of food; however it is not always possible. Addressing any nutritional inadequacy through measured supplementation, provides insurance that the body is getting the nutrients that it needs.
It is important to note that genetic differences mean that the conversion of specific nutrient precursors (like beta-carotene and alpha-linolenic acid) into the active forms of those nutrients (like retinol and EPA and DHA, respectively), differs amongst individuals, and that these genetic differences influence the duration which an individual is able to maintain a vegetarian or vegan diet prior to developing any nutrient deficiencies in the absence of supplementation, which explains why some people seem to cope well for years on these diets, while others develop problems very quickly.
With a regimented diet however it is possible to meet nutrient requirements by consuming a vegetarian or vegan diet. However it is also necessary to supplement with EPA and DHA as these long-chain omega fats are found exclusively in marine algae and fish and shellfish. Therefore, it is only possible to get them form a microalgae supplement in a vegetarian or vegan diet. Even in its absence, it may be possible to obtain sufficient nutrients on a vegetarian or vegan diet, but it would not be optimal. When following a vegan diet, it is also beneficial to supplement with vitamin B12, zinc, calcium, vitamin A and vitamin D, in order to ensure that nutrient requirements are met.
Ultimately, the right diet for anybody is dependent on a number of physiological, social, cultural and economic factors. A diet which is appropriate for one individual, may not be appropriate for another. If you choose to consume a vegan diet, ensure that you are conscientious with your diet and supplements.