Note: this is one of my oldest posts, written when I was 19. I’m sure there are FAR better and more comprehensive summaries out there of the nutritional risks of a vegan diet, but this post (along with part one) do cover the high points, so I’ve left them up!

In part one, I discussed whether it’s possible to get enough vitamin D, calcium and vitamin K2 – three nutrients that are vital to bone health – on a vegan diet, without using supplements. We discovered that it is possible, but only if you get lots of sunlight, eat plenty of greens, properly prepare your nuts and seeds, and eat natto. In this post I’ll wrap it up by looking at iron, zinc, vitamin A, and vitamin B12. Then we can finally answer the question: Is it possible to be healthy on a vegan diet without the use of supplements?

Iron and Zinc

Iron and zinc, like vitamin D, are significantly more bioavailable in animal products than in plants. Iron comes in two forms: non-heme iron, which is found in plants, and heme-iron, which is found in animals. (‘Heme’ refers to ‘hemoglobin,’ which is the molecule that binds to iron in the blood.) On average, serum ferritin (a measure of iron status) tends to be lower in those following a vegan diet than in those following an omnivorous diet, although the risk of iron deficiency anemia appears to be similar. (1)

Unsurprisingly, whole vegans and raw vegans will likely fare much better than SAD vegans because their higher intake of unprocessed fruits and vegetables will afford them much higher levels of vitamin C, which markedly increases the absorption of non-heme iron. (2) However, there are several factors even in a seemingly healthy ‘whole vegan’ diet that could be cause for concern: vegan diets can be high in phytates from whole grains and soy, which have been shown to significantly reduce the absorption of non-heme iron. (3) Phytates have similar inhibitory effects on zinc absorption. (4)

Zinc also tends to be better absorbed when accompanied by higher levels of protein, so the relatively low-protein diet of a vegan might reduce the efficiency of zinc absorption. (5) Fermentation and sprouting of grains and legumes significantly lower their phytate content, so in addition to improving calcium absorption, these traditional practices could be extremely important in making sure vegans get enough iron and zinc.

Vitamin A

The next nutrient I want to address is vitamin A. If you think vitamin A is found in carrots and sweet potatoes, your high school nutrition class did you a disservice. These vegetables (and other plant foods) are actually high in beta-carotene, which is a precursor to vitamin A, but is not the real thing. Retinol is the ‘real’ vitamin A, the biologically active form that protects your eyesight and other good stuff. Unfortunately, retinol is only found in animal products.

The absorption of beta-carotene in humans varies widely, and the conversion of that beta-carotene into retinol isn’t very efficient. (6) Factors that influence this process include the fiber content and processing of the food, digestive health, and nutrient deficiencies, as well as some genetic factors that are completely beyond our control.

In a vegan who is gloriously healthy and who is eating a variety of beta-carotene rich vegetables (along with a healthy amount of fat to increase absorption), I wouldn’t worry about vitamin A status, so I definitely think it’s possible to maintain healthy vitamin A levels on a vegan diet without supplementation. However, for someone with a compromised absorption-conversion pathway, supplementation is probably necessary to avoid problems. It’s also worth noting that iron and zinc are necessary for converting beta-carotene to vitamin A, so if you’re deficient in those two minerals, you might be deficient in vitamin A as well. (7)

DHA (Docosahexaenoic acid)

That’s an impressive name, isn’t it? Maybe one of these days I’ll actually be able to pronounce it correctly on the first try. Anyways, DHA is a long-chain omega-3 fatty acid that is vital to the proper functioning of the immune system, and it likely played a role in the evolutionary development of the modern human brain. (8) You’ll find some great information on the importance of DHA here and here.

There are a few different omega-3 fatty acids, including DHA, EPA, and ALA. ALA is the kind found in plant foods like flax, while EPA and DHA are found only in seafood and algae. Thus, vegans don’t get any DHA in their diet unless they’re taking an algae supplement. The current belief is that ALA is the only omega 3 fat we must get from our food, but evidence is mounting that DHA is the true ‘essential fatty acid.’

The conversion of ALA into DHA is much lower than previously thought: only 2-5% of dietary ALA is converted into DHA, and that conversion rate is even lower in people with micronutrient deficiencies. (9) One study shows that the level of DHA in the blood, tissues, and breast milk of vegans is much lower than in omnivores, and that the level of omega-6 fats is much higher. (10) Additionally, ALA supplements did not increase tissue levels of DHA, while pre-formed DHA supplements increased tissue DHA dramatically.

In his report on essential fatty acids, Chris Masterjohn makes the case that in order to be optimally healthy, humans must get pre-formed DHA from their diet. This would mean that vegans must take an algae-derived DHA supplement, because there are no vegan food sources of DHA.

I think this is another instance where your mileage may vary. Someone with an extremely efficient ALA to DHA conversion pathway, no micronutrient deficiencies, and a low intake of the omega-6 fat linoleic acid (which can impede DHA formation) may be able to maintain health on a vegan diet without a DHA supplement, but I think the vast majority of vegans would probably see health improvements if they started taking DHA.  

Vitamin B12

Alright folks, here’s the kicker. So far, we haven’t run into any nutrients that would render a vegan diet (sans supplementation) completely unsustainable. If you live near the equator, eat plenty of greens, regularly consume natto, always soak your seed-like edibles, liberally slather your sweet potatoes with coconut oil, and have an abnormally efficient ALA conversion pathway, you should be fine with regards to vitamin D, calcium, vitamin K2, iron, zinc, vitamin A, and essential fatty acids. But I don’t think you’re going to be able to escape vitamin B12.

This innocent little B-vitamin is frequently used as ammo against the vegan community, leaving them with little to defend themselves but trembling teaspoons of nutritional yeast. Not to beat a dead horse, but really – vitamin B12 is only found in animal foods. You can’t get it from plants. Vegans have been shown to have much lower levels of vitamin B12 than vegetarians or omnivores, likely with serious consequences. (11, 12) The “vitamin B12” found in plant-based supplements such as yeast and spirulina is not true vitamin B12. In fact, it looks like those B12 analogues could potentially make a B12 deficiency worse. (13) If you are a vegan, you really, really, really should supplement with vitamin B12.

A Note About Gut Bacteria

I believe that the ability of a person to stay healthy on a vegan diet is closely tied to the state of their intestinal flora. Take vitamin K2, for example: some of our gut bacteria can produce vitamin K2, which some people absorb. (14, 15) Between that and the limited conversion of K1 to K2, I wouldn’t be surprised to find a vegan who could avoid K2 deficiency without supplementing and without suffering through bowls of natto. This is especially true if they don’t have other nutrient deficiencies or health issues.

The same might be said for vitamin B12. In some populations, the production of vitamin B12 by intestinal bacteria appears to contribute significantly to B12 status, but in communities with different populations of gut flora, B12 production by intestinal flora is negligible or not well absorbed. (16) So maybe, just maybe, not all vegans need to supplement with B12, but since one study found that half of vegans were B12 deficient, and another using more sensitive testing methods found that 83% of vegans were deficient, I’d say supplementing is still the smart thing to do. (17, 18)

If a vegan is able to stay healthy while avoiding B12 supplementation, I give credit to their gut bacteria and superior genetics. However, in modern, westernized societies where antibiotics and hand sanitizer reign supreme, I doubt most of our gut bugs are up to the task of efficient K2 and B12 production.

Conclusion

My purpose with this post isn’t to prove that you shouldn’t be vegan because it’s bad for your health. If you’re careful and you have the genes (and gut bugs) for it, I don’t think it is. Rather, it’s a response to anyone who claims that a) humans are meant to be vegans; b) the healthiest diet is a vegan diet; or c) all humans should be vegan. None of these things can be true, because for the vast majority of people, it is not possible to be healthy on a vegan diet without the use of supplements. And how can you claim any of those things for a diet that requires scrupulous planning and an arsenal of pills in order to work properly? Plus, for many people with compromised digestive systems, it wouldn’t be possible to be a healthy vegan even with all the supplements in the world.

A person’s ability to thrive on a vegan diet hinges on their ability to absorb the plant forms of nutrients (which are less bioavailable than their animal forms), as well as their genetically and environmentally programmed ability to convert compounds such as beta-carotene and ALA into their bioactive forms. But even if all those factors are in line, vegans would need an extremely unique population of intestinal flora in order to avoid the need for B12 supplementation.

So to give a straight answer to the question: Yes, it’s probably possible for a very small percentage of people to be healthy on a vegan diet without the use of supplements. I’ve seen people claim to be healthy, long-term vegans who don’t supplement. I take people at their word, so if you tell me you’ve been a thriving vegan for 50 years with nary a B12 supplement, I’ll believe you. (I’ll also be intensely jealous of your gut bacteria.) But based on the evidence presented here, I’d say you’re in the lucky minority.

That’s it! Hopefully I covered all the important points. Here are all the posts in the series:

Veg*n is Not a Curse Word
Plant-Based Diet or Plant-Based Diet?
Are Humans Herbivores?
Is it Possible to be Healthy on a Vegan Diet? [Part One]
Is it Possible to be Healthy on a Vegan Diet? [Part Two]
A word on raw meat, carnivory, and compassion towards animals