2 carrots provide all the vitamin A you need for one day.

A number of readers have asked if I’d respond to the article Why You Should Think Twice About Vegetarian and Vegan Diets, by Chris Kresser. Kresser is a licensed acupuncturist who writes frequently about diet. And since I would never go around poking needles into people, I wish he would return the favor and stop giving advice about nutrition.

Kresser promotes a semi-Paleo eating pattern so it’s no surprise that he’s not a fan of vegetarian diets. But in his effort to prove that plant-based eating is unhealthy, he uses some very faulty logic. Jack addressed Kresser’s observations about vegetarian diets and longevity, so I’ll look at some of the other tired old arguments that Kresser drags out to discredit veganism.  Here are some examples (Kresser’s comments are in bold).

A common myth amongst vegetarians and vegans is that it’s possible to get B12 from plant sources like seaweed, fermented soy, spirulina and brewers yeast.

True enough. But picking at the harmful myths that circulate in the vegan community does not provide evidence that vegan diets are dangerous. It just provides evidence that being uninformed about nutrition is dangerous. Vegans who take vitamin B12 supplements do just fine, and as Jack noted, they probably are doing better in this regard than many meat-eaters.

[Plant-based diets] typically include large amounts of cereal grains (refined and unrefined) and legumes, both of which are low in bioavailable nutrients and high in anti-nutrients such as phytate […]

I’ll get to phytate in a minute. But first, do vegans and vegetarians eat more refined grains than meat-eaters? I doubt it. People eating any type of diet—omnivore, lacto-ovo vegetarian, and vegan—can make good or bad choices. It doesn’t say anything about the potential of a particular eating pattern to be adequate and healthy. Everyone—meat eaters, vegetarians and vegans—should minimize refined grains in their diets. This has absolutely nothing to do with whether or not vegetarian diets are healthy. And the evidence just doesn’t support the idea that eating moderate amounts of whole grains is harmful.

Calcium bioavailability from plant foods is affected by their levels of oxalate and phytate, which are inhibitors of calcium absorption and thus decrease the amount of calcium the body can extract from plant foods. So while leafy greens like spinach and kale have a relatively high calcium content, the calcium is not efficiently absorbed during digestion. 

One study suggests that it would take 16 servings of spinach to get the same amount of absorbable calcium as an 8 ounce glass of milk.

Anyone claiming expertise in plant-based nutrition knows that calcium is very well-absorbed from cruciferous vegetables, which include kale. In fact, the chart Kresser links to when making his point about spinach shows the absorption rate for kale—49.3 percent—sitting right smack above the one for spinach.

We do need to eat bigger servings of most (not all) vegetables to get the same amount of calcium from a glass of milk. But who says that every serving of a calcium-rich food has to provide the same amount of calcium as a glass of milk? We get small amounts of calcium from many different foods, most of which are also good sources of other bone-building nutrients. As long as they add up to provide enough calcium, it hardly matters that you need to eat 1 ½ cups of cooked kale to get the calcium that would be provided by a glass of cow’s milk.

Vegetarians eat a similar amount of iron to omnivores, but as with calcium, the bioavailability of the iron in plant foods is much lower than in animal foods. […] This explains why vegetarians and vegans have lower iron stores than omnivores.

But Kresser doesn’t address the fact that having lower iron stores is not necessarily a bad thing. There is evidence that lower iron stores can protect against chronic disease.(1) The ideal situation might be to have lower but adequate stores.

Furthermore, the lower iron stores in vegans and vegetarians are due largely to the presence of phytate in foods. This compound binds iron and other minerals which reduces their absorption. However, phytate, long demonized as an antinutrient, is actually an antioxidant with health-promoting properties.(2) We can free iron from phytate by including vitamin C rich foods in a meal, sprouting grains and beans, or fermenting them—which is what happens when we make whole grain flour into any type of leavened bread. It’s possible that the ideal situation is a diet that includes phytate along with factors, like vitamin C-rich foods, that increase iron absorption from plants.

Freeing zinc from phytate is admittedly more difficult because zinc doesn’t seem to be affected by vitamin C in the diet. Its absorption is, however, enhanced by sprouting, leavening and fermenting.

Perhaps the biggest problem with vegetarian and vegan diets, however, is their near total lack of two fat-soluble vitamins: A and D.

Oops—it’s a common mistake to think that vitamin D is a vegan issue. We vegans get our vitamin D the same way that meat-eaters do: from sun exposure or fortified foods. Cow’s milk is fortified with vitamin D just like soymilk. Granted, you could technically get vitamin D by eating fish but you’d have to eat salmon or swordfish every day. That’s hardly a sustainable answer to meeting vitamin D needs.

While beta-carotene is converted into vitamin A in humans, the conversion is inefficient. For example, a single serving of liver per week would meet the RDA of 3,000 IU. To get the same amount from plant foods, you’d have to eat 2 cups of carrots, one cup of sweet potatoes or 2 cups of kale every day.

It actually takes somewhat less than one cup per day of winter squash, carrots, kale, or spinach, or ½ cup of sweet potatoes to meet daily vitamin A needs. And the provitamin A in these foods is an antioxidant associated with lower risk of chronic disease.(3) You won’t get that benefit from liver.

Moreover, traditional cultures consumed up to 10 times the RDA for vitamin A. It would be nearly impossible to get this amount of vitamin A from plant foods without juicing or taking supplements.

And why would we want to? There are no advantages to getting ten times the RDA of any nutrient. In fact, if all of this vitamin A were coming from animal foods, it would put people dangerously close to the upper limit of safety for vitamin A. If anything, this observation suggests that it’s not always ideal to look to traditional or ancestral cultures for information about how we should eat.

However, an increasing body of research has highlighted the benefits of the long-chain omega-3 fatty acids EPA & DHA. These fatty acids play a protective and therapeutic role in a wide range of diseases: cancer, asthma, depression, cardiovascular disease, ADHD, and autoimmune diseases, such as rheumatoid arthritis.

This is way overstating the evidence. Results of studies on benefits on these fats have been conflicting(4,5) and we currently have more questions than answers about their roles in healthy diets. I’m not saying that omega-3’s aren’t important. I think they may be, but I wouldn’t state their benefits in quite so definite terms. Nevertheless, there are vegan sources for those who want to supplement their diets.

From an evolutionary perspective, it is difficult to justify a diet with low levels of several nutrients critical to human function. While it may be possible to address these shortcomings through targeted supplementation (an issue that is still debated) it makes far more sense to meet nutritional needs from food.

This begs the question: If the ideal diet doesn’t require supplements, and Kresser promotes the ideal diet, then why is he selling all types of expensive supplements in his online store?

We did not evolve on a vegan diet, that’s true. But we live in a much more complex world than that faced by our Paleolithic forebears. We need to look at dietary choices in terms of our personal health but also in terms of the health of the planet and the creatures who share it with us. Fortunately, we also have the knowledge and resources that allow us to make responsible dietary choices that are a good fit to this modern world. If it takes a little bit of extra work, so be it. Eating a little extra kale and taking a vitamin B12 supplement (which I would have to do anyway since I’m over 50) don’t seem like hardships for anyone who wants to eat ethically, compassionately, and responsibly.

1.   Postmenopausal Vegetarians’ Low Serum Ferritin Level May Reduce the Risk for Metabolic Syndrome. Kim MH, Bae YJ. Biol Trace Elem Res   2012.
2.   Protection against cancer by dietary IP6 and inositol. Vucenik I, Shamsuddin AM. Nutr Cancer 2006;55:109-25.
3.    Dietary carotenoids and risk of coronary artery disease in women. Osganian SK, Stampfer MJ, Rimm E, Spiegelman D, Manson JE, Willett WC. Am J Clin Nutr 2003;77:1390-9.
4.    Association between omega-3 fatty acid supplementation and risk of major cardiovascular disease events: a systematic review and meta-analysis. Rizos EC, Ntzani EE, Bika E, Kostapanos MS, Elisaf MS. Jama 2012;308:1024-33.
5.    Role of n-3 fatty acids in the treatment of hypertriglyceridemia and cardiovascular disease. Jacobson TA. Am J Clin Nutr 2008;87:1981S-90S