Vegan diets have dramatically increased in popularity over the last 10 years. There has been a 350% increase in vegan diets in the UK (1), and similar increases worldwide. In Israel, almost 5% of the population now identifies as vegan (2). I have previously discussed the reasons for this explosion in popularity, likening it to a stock market bubble. However ideas, unlike market bubbles, do not burst. They rise and fall on the success of that idea, this is known as memetics (nothing to do with internet memes!). This post will be a dietary assessment of the vegan diet, and will not deal with the ethical and sustainability arguments.
Vegan Diets Are Deficient In Essential Nutrients:
Animal foods (meat, fish, poultry, eggs, dairy) are the only significant source of B12 and B12 is found almost exclusively in animal foods. Therefore, someone who consumes a diet without animal foods will become B12 deficient. B12 is stored in our liver and there is sufficient supply for a few years. So, a true B12 deficiency takes a while to show up in vegans.
There are 3 plant foods that contain B12 in significant amounts: tempe, nori seaweed, and shiitake mushrooms. However, tempe can vary widely in how much B12 it has: 0.7–8.0 mcg/100 g, so is not be a reliable source of B12. Moreover, you would need to eat 50g of dried shiitake mushrooms to achieve the RDA of 2.4mcg, which is about a pack a day. However, green nori contains 63.6 mcg/100g and purple nori contains 32.3 mcg/100 g (3). So a couple of sheets of green nori would fulfill your daily B12 requirement (4).
Vitamin A in animal foods is found in the active form called retinol. However, vitamin A in plant foods is in the form of carotenoids, which must be converted into retinol before being used in the cells. The enzyme responsible for this conversion is beta-carotene 15,15′-monoxygenase, which is encoded by the BCMO1 gene.
Common variations on this gene and genes near it reduce the rate of conversion. Making 27-45% of people poor converters of carotenoids (5). These people convert carotenoids at a rate of 10 times less than normal converters (6). Therefore, a significant number of people would end up vitamin A deficient on a vegan diet. They would have to eat about 14 carrots to get their daily requirement!
Iron comes in 2 different forms heme and non-heme iron. Heme constitutes roughly half of the iron in meat, poultry, fish, and seafood. The other half is non-heme. In contrast, all of the iron in plant foods is non-heme.
About 15% of heme iron is absorbed, and 7% of non-heme iron (7). Furthermore, phytic acid, oxalic acid, and vegetable protein inhibit iron absorption (8). These are found exclusively in plant foods. In addition, heme iron actually increases non-heme iron absorption, so the non-heme iron contained in meat is better absorbed than that in plants (9).
There are 3 types of omega 3 fats: ALA (alpha-Linolenic acid), DHA (docosahexaenoic acid), and EPA (eicosapentaenoic acid). ALA is found in plant foods and DHA and EPA are found in animal foods, particularly oily fish.
Only ALA is strictly essential since the body cannot synthesize it. The body can synthesize EPA from ALA, and then DHA from EPA (The Full Conversion: ALA → EPA → DHA). However, the conversion rate to DHA is below 5% and this may be further lowered by a high intake of omega 6s (vegetable oils) (10). Therefore, to achieve adequate amounts of EPA and DHA we must intake them directly, from dietary sources (11).
The majority of the research on omega 3s has focused on the benefits of EPA and DHA, such as the role of DHA in the brain. Moreover, the cardioprotective benefits of EPA and DHA are much greater, than ALA (12,13,14). So a vegan diet that only includes ALA does not have the same benefit as a diet including EPA and DHA (oily fish). Vegan diets are deficient in EPA and DHA and an increased intake of ALA cannot make up for this.
Oxalic Acid and Phytic Acid
Plant foods contain oxalic acid and phytic acid which bind to minerals and inhibit their absorption. They have strong effects on zinc, iron, magnesium and calcium absorption (15, 16, 17, 18, 19). With careful preparation, levels of phytic acid can be reduced and the minerals made more bioavailable. However, this issue shows that the minerals in animal foods are more bioavailable than those in plant foods.
The 4 Micronutrient Deficiencies on a Vegan Diet
The micronutrient deficiencies a vegan diet will cause are:
- Vitamin B12. Unless you eat nori daily, you will end up B12 deficient on a vegan diet.
- Vitamin A. 27-45% will become vitamin A deficient on a vegan diet.
- Iron. Iron is much easier to absorb from animal foods and vegans are at high risk of deficiency.
- Omega 3s. Vegan diets do not contain DHA and EPA and vegans will become deficient in these important fatty acids.
What Diet Were We Designed to Eat?
Looking at these 4 micronutrient deficiencies brings up an important question. What diet were we designed to eat? This is important because humans eating their traditional diets, the diets their ancestors had eaten for generations, have been found to be in excellent health. As there is only one appropriate plant source of B12 (nori). It is clear the vast majority of humans would not have had access to this. Therefore in the past, we must have relied on animals foods for our B12, which are found everywhere.
Hunter-gatherer diets and agricultural diets all show regular intake of animals foods (20). Moreover, these foods were highly favoured and sought after by hunter-gatherers:
Our analysis showed that whenever and wherever it was ecologically possible, hunter-gatherers consumed high amounts (45-65% of energy) of animal food. Most (73%) of the worldwide hunter-gatherer societies derived >50% (> or =56-65% of energy) of their subsistence from animal foods, whereas only 14% of these societies derived >50% (> or =56-65% of energy) of their subsistence from gathered plant foods. (21)
History of Vegan Diets
Vegan diets have been almost nonexistent until the 20th century, and no society has relied upon them. In the past, it was only a few Indian philosophers and Buddhists who ate vegan.
Both living foodism and veganism emphasize the importance of ‘natural’ foods, yet both are very much products of modern individualistic culture. (22)
There is no historical precedent for veganism and it is not the ‘natural’ diet of humans. Homo sapiens are omnivores and require both plants and animals to thrive. Excluding, all animal foods is extreme and forces an omnivorous species to become a herbivore.
- There are no appropriate plant sources of B12, apart from nori. Therefore, vegans who do not supplement will end up deficient.
- 27-45% of people are poor converters of carotenoids to active vitamin A. Therefore, they must rely on animal sources of vitamin A to avoid deficiency.
- Iron is far easier to absorb from animal sources, than plant sources.
- Vegan diets do not contain sources of DHA and EPA; and vegans must supplement to avoid deficiency. ALA is not an appropriate substitute.
- Oxalic acid and phytic acid in plant foods inhibit mineral absorption. These must be taken into account on a vegan diet.
- Hunter-gatherer societies heavily relied on animal foods, and agricultural societies also included regular intake of animal foods.
- Veganism is a distinctly 20th-century phenomenon.