People decide to follow a vegetarian or vegan for many reasons. Some because of the environmental impact and others for ethical concerns or on religious grounds. These reasons deserve respect and appreciation for considering the broader implications of their food choices.
Some people also choose a vegetarian or vegan diet because they believe it is a nutritionally healthier choice. But is this true? In this article, we endeavour to answer this question by examining the nutritional status and mortality rates among people who follow a plant-based diet.
Since the 1960's, food policymakers have told us that eating animal products is hazardous to our health. For this reason, most people will consider a vegetarian or vegan diet healthier than one that contains meat and eggs. To learn more about other types of diets such as Leangains, click here.
Vegetarian and vegan diets feature vegetables that are full of nutrients. At the same time, however, these diets also include considerable amounts of grains and legumes (beans). Grains and beans are both low in bioavailable nutrients and high in anti-nutrients such as phytates.
Vegan foods, in particular, are inherently entirely lacking specific nutrients that are critical for the body to function. Numerous studies have shown that people who follow plant-based diets are likely to develop deficiencies in vitamin B12, calcium, iron, zinc, the fatty acids EPA and DHA, and fat-soluble vitamins like A and D.
Let us consider more closely the status of these nutrients in the context of a vegetarian or vegan diet.
According to research, the absorption of calcium is comparable in vegetarians and meat-eaters but is considerably lower in vegans. Plant foods contain oxalate and phytate that affect the bioavailability of calcium bioavailability. So the calcium in plant foods is not efficiently absorbed during digestion of leafy greens like spinach and kale even though they have a comparatively high calcium content.
One study concluded that it would require multiple servings to achieve the same amount of bioavailable calcium as in a single serving of milk. This conclusion suggests that seeking to satisfy your daily calcium requirements from plant foods alone may not be achievable.
The intake of iron for meat-eaters and vegetarians are similar according to research findings. The levels of iron stores, known as ferritin, however, are lower in vegetarians than in meat-eaters. Ferritin deficiency is meaningful because it is the first indication of iron insufficiency. Thus, although vegetarians have similar iron intakes to meat-eaters omnivores, it is more common for vegetarians (and particularly vegans) to be iron deficient. For example, a study looking at 75 vegan women observed that 40% were iron deficient, despite their intake of iron being above the recommended daily allowance.
How is this possible?
Like calcium, the bioavailability of the iron in plant-based foods is much lower than in animal-based foods. Iron from plants is also hindered by other regularly consumed foods, such as coffee, dairy products, and tea. This fact illustrates why vegetarians have been shown to have lower non-heme iron levels and reduced total iron absorption.
Vegetarians that live in Westernised countries contract a frank zinc deficiency rarely, but their consumption frequently drops under the recommended daily allowance (RDA). Like calcium and iron, zinc bioavailability in plants is low because they also contain anti-nutrients such as phytates. Research shows that absorption of zinc is 35% lower in vegetarians compared to meat eaters. Therefore, a zinc deficiency may occur even when the diet meets the RDA. Interestingly, for this reason, vegetarians may need to consume up to fifty per cent more zinc than meat-eaters.
The lack of vitamin A and D is arguably the most significant nutrient deficiency with vegetarian and vegan diets. Vitamin A and D play essential roles in immune function and metabolism.
Food sources of vitamin A and D are almost exclusively from animal products including dairy, eggs, organ meats and seafood. Vitamin D may be found in an obscure species of mushroom. However, these mushrooms are rarely consumed and are difficult to purchase. These facts may explain why meat-eaters have high levels of vitamin D than both vegetarians and vegans.
A common misunderstanding is that plants contain Vitamin A. Rather, plants contain beta-carotene which is the precursor to vitamin A. The conversion of beta-carotene into vitamin A in the body is poor. An excellent source of vitamin A is liver. A single serving of liver per week contains 3,000 IU of vitamin A. To obtain the same amount from plant foods you would have to consume two cups of carrots every day for a week.
Vegetarians and vegans are especially predisposed to vitamin B12 deficiency. Recent studies have found that sixty-eight per cent of vegetarians and eighty-three per cent of vegans are B12 deficient, compared to just five per cent of people that eat animal products.
B12 deficiency can cause numerous problems from fatigue to anxiety.
Children are particularly affected by vitamin B12 deficiency. Research has shown that children raised on a vegan diet until age six were still B12 deficient many years later. In one study, the researchers observed a link between B12 status and the performance of children on tests gauging fluid intelligence, spatial ability and short-term memory. Previously vegan youngsters were also shown to score lower than meat-eating children.
The researchers said that the deficiency in fluid intelligence was particularly troubling because it involves the capacity to solve complex problems, reasoning, and the ability to learn and think abstractly.
A common misconception is that it is conceivable to acquire B12 from plants like brewers yeast, fermented soy, seaweed and spirulina. The B12 in plants is not very bioavailable because they contain cobamides that block the intake of B12.
EPA and DHA are essential fatty acids (EFA). DHA and EPA play a crucial protective in the body. Plant foods do not include DHA or EPA but contain the EFA's linoleic acid and alpha-linolenic acid. The body can convert some alpha-linolenic acid into DHA and EPA; however, the conversion is inefficient. Therefore, it is no surprise that DHA and EPA levels found in meat-eaters are higher than in vegetarians and vegans.
According to some observational studies, vegetarians and vegans live longer than meat-eaters. The results of these studies are however swayed by something called the "healthy user bias". The healthy user bias is the technical way of stating that a person who participates in a behaviour that is considered as healthy (whether it is or not) are more inclined to partake in other practices that are healthy. For example, vegetarians are more health conscious on average than the general population, and as such, they are more liable to exercise, eat fruits and vegetables and take care of themselves, and less prone to drink or smoke to excess.
The opposite of this rule is also valid. A person that participates in behaviours regarded as harmful is more apt to partake in other deleterious behaviours. For example, people that eat highly processed commercial meat products are less health conscious on average and as such are less likely to exercise, eat fruits and vegetables and more likely to drink and smoke excessively.
With the health user bias in mind, it would difficult to ascertain from the above observational studies whether it was diet alone or other factors that determined why vegetarians and vegans live longer than meat-eaters.
So, how can we overcome the healthy user bias issue?
To answer that question researchers designed a study that attempts to overcome the healthy user bias. To do this, the researchers compared meat-eaters and vegetarians that were both health conscious. The study looked at the lifespan of meat-eaters and vegetarians who shopped in health food stores. The thinking was that people who buy from health food stores were more likely to be health conscious.
The researchers found that both meat-eaters and vegetarians that shopped at health food stores had an equal and longer lifespan.
Evidence suggests that in general, a vegetarian diet is deficient in particular nutrients. That said it would be possible with the inclusion of generous amounts of grass-fed and eggs to meet adequate nutritional requirements with a vegetarian diet. The exception to this statement is EPA and DHA. These essential fatty acids are found only in fish and shellfish. So, the only way to obtain them while following a vegetarian diet would be to bend the rules and take a fish oil supplement. However, while it may be feasible to achieve adequate nutrition on a vegetarian diet, it is not optimal as the research above shows.
Vegan diets are also deficient in essential nutrients and would require many nutritional supplements to meet even adequate needs. Vegan foods are low in the calcium, B12, DHA and EPA, iron, vitamins A and D, and zinc. Therefore, it is advisable to supplement with these nutrients when following a vegan diet.
Interestingly some people have genetic mutations that affect the conversion of particular nutrient precursors into the active forms. For example, a gene mutation may slow down the conversion of beta-carotene into vitamin A. These genetic mutations may explain why some people appear to do fine on these diets for years, while others develop problems due to nutritional deficiencies very quickly.
From a professional perspective, it is difficult to recommend diets that are low in nutrients critical to optimal human function. It may be plausible to overcome these deficiencies through supplementation, but it makes far more sense to satisfy nutritional requirements from food. This approach is particularly critical for children, whose development is far more sensitive to suboptimal nutrients deficiencies.
Now I’d like to hear from you. Let us know in the comments below.
