How “Science-Based Medicine” Gets Vegan Diets Wrong

How “Science-Based Medicine” Gets Vegan Diets Wrong

By | 2016-07-13T07:56:08+00:00 July 13th, 2016|24 Comments

science and vegan dietsThe latest book to capitalize on anti-veganism is by science writer Mara Kahn (and, yes, of course, she’s also an ex-vegan). It’s called Vegan Betrayal: Love, Lies and Hunger in a Plants Only World. I can’t comment much on the book since I haven’t read it. But I can comment on a review of the book that appeared on the Science Based Medicine (SBM) website.

Written by SBM co-founder Dr. Harriet Hall, it was more a synopsis of the book’s contents than a thorough review. It was also an endorsement for a number of non-science-based myths about vegan diets.

Usually, I find the SBM website to be balanced and evidence-based. Its writers (including Dr. Hall) are smart and insightful and I often agree with their criticisms of popular vegan claims. This article, though, displayed an incredible bias against veganism. Or maybe just a lack of knowledge about vegan diets. Whichever it is, it has no place on a website that prides itself in being evidence-based.

Dr. Hall didn’t claim to like all of the book (more on that below) but she recommends—“highly recommends,” in fact—the part that addresses vegan nutrition. Based on what I saw in her review, I don’t think I agree.

For example, Kahn claims that “Research has shown vegan deficits in many key nutrients including iodine, iron, zinc, taurine, vitamins A, D and B12, selenium, protein, calcium and omega-3 fatty acids.”

We’ve all seen these statements before—the kind that bundle misinformation with misleading observations. For example, vegans have about the same risk for iron deficiency anemia as non-vegetarians. It’s not that this is necessarily a good thing, since iron deficiency anemia is a serious and common problem. But pointing out that vegans might be deficient is misleading if you’re trying to make the case that vegan diets are inferior to those that contain meat.

Also, the last time I checked, taurine was not considered to be a nutrient let alone a “key” nutrient.

It’s true that poorly planned vegan diets can be too low in vitamins A, D and B12, calcium, zinc, iodine, essential omega-3 fats, and (in some parts of the world, but not the United States) selenium. Non-vegetarian American diets have also been found to be low in vitamins A and D, and in calcium, as well as in vitamin E, folate, vitamin C, magnesium and fiber. Meat-eaters over the age of 50 may also be deficient in vitamin B12 if they aren’t using supplements or fortified foods.

So, meat-eaters do better with some nutrients and vegans do better with others. No particular dietary pattern guarantees adequate nutrient intake and therefore this is not an argument for or against veganism. Nor it is an argument for or against diets that include meat. It just means that no matter what dietary pattern you choose, you should pay attention to nutrient intake.

But, Dr. Hall says that Ms. Kahn “observes vegans eating huge amounts of carbs and vegan junk foods and skimping on their protein and vitamin needs.” 

Why would someone writing for a blog called Science-Based Medicine care what a layperson  “observes” when those observations aren’t backed by research? Vegans consume diets that get about 10 to 14% of calories from protein and are about 30% fat—so are not particularly low in either of these macronutrients. Vegans may have higher carb intakes than non-vegetarians but since they also have lower average BMIs and a much lower risk for diabetes, it’s not likely that this is a problem.

And the claim that vegans eat large amounts of junk foods stands in stark contrast to the observation just a few paragraphs later that “vegans may feel better at first simply because they are eating fewer calories and have replaced processed and junk foods with healthier fruits, vegetables, and grains.”

So which is it—are vegans at risk for health problems because they eat so much junk, or do they benefit from the fact that they eat less junk?

And then there is this observation about meeting protein needs: “It may be possible for individuals with naturally lower protein needs who can tolerate large amounts of legumes, lead low-stress lives […] and keep a vigilant eye on daily quantity, quality, and amino acid completeness. Easy? No, it is not.”

Easy? Yes it is. It involves meeting calorie needs and including a few servings of lysine-rich foods like beans, soyfoods, peanut butter or quinoa in your diet every day. You have to be seriously stuck in the 1980s to think that we need to keep a “vigilant eye” on “amino acid completeness.”

Finally, it wouldn’t be a good ex-vegan/anti-vegan article without some fearmongering about soy. Dr. Hall writes: “Vegans often rely on soy for protein, but soy can be harmful to health in various ways.”

But is this Dr. Hall’s opinion or Ms. Kahn’s? As with much of this review, it’s not entirely clear. Either way, it is irresponsible to toss such a vague, unsubstantiated statement into the article without challenging it.

In the comments following the article, a moderator argues that this was a book review, not an article that shares Dr. Hall’s opinions. But the fact is that Dr. Hall does get around to criticizing some of the content of the book in a section she titles “Woo Intrudes.” Here she challenges Kahn’s opinions on GMOs, statins, and fructose as “alarmist and not based on rigorous science.” Why didn’t she likewise challenge the section on vegan nutrition in this way? It’s because she believes that “on the subject of veganism, Kahn’s information is evidence-based and reliable and her reasoning plausible.”

As far as I can tell, it’s none of the above. But, I must admit, there are some legitimate criticisms in the book and in the review. It is fair to challenge vegans who claim that humans evolved as herbivores. We didn’t; we’re omnivores who have the option to eat herbivorously. It’s legitimate to accuse vegans of over-reaching if we claim that a vegan diet is the only healthy way to eat. The evidence doesn’t support that, and it’s likely that there are other plant-based patterns that are as healthy.

Had the book and the review stuck to those kinds of issues, the criticisms would have been valid.  But for both sides of the discussion—pro- and anti-vegan—bias and misinformation and half-truths trip us up. We vegans need to avoid that. And the Science-Based Medicine website owes its readers an actual science-based review of Ms. Kahn’s book.


  1. Marsha July 13, 2016 at 10:58 am - Reply

    Would love to see Facebook links to these articles so I can share! 🙂

  2. Gordon Hanzmann-Johnson July 13, 2016 at 1:12 pm - Reply

    “Finally, it wouldn’t be a good ex-vegan/anti-vegan article without some fearmongering about soy.”


  3. Mark July 13, 2016 at 1:36 pm - Reply

    This is excellent work, Ginny. Thank you.

  4. Rob Jewett July 14, 2016 at 5:03 pm - Reply

    I could not agree more with Mark, Ginny. Excellent review. When I first saw Dr. Hall’s article, I could only shake my head in disbelief. This is the second article she has led me to question the value SBM provides in the area of nutrition. Some time last year she “reviewed” one of Dr. Greger’s annual presentations on YouTube. When I read her review, it was so snarky (as is this article to some extent) that I wondered if she gave it more than 5 minutes and fast-forwarded through the rest of it. Thank you for your work in calling out this current flawed review.

  5. Lisa @ The Valley Vegan July 14, 2016 at 6:13 pm - Reply

    All I kept thinking while reading this is why is it so important for people to debunk Veganism?! It drives me nuts. So much attention on why Veganism is “bad” for people, and yet little attention on the perils of eating meat. Ugh. Drives me nuts.

    Great job, Ginny. Always making sense of this stuff for us!!

  6. Ernest July 19, 2016 at 12:20 pm - Reply

    The are many things going on with vegan diets:

    1. They are getting more and more followers.
    2. For health, evidence is clearly moving in favor of plants and against animal products.
    3. Obesity is rampant and vegans tend to have lower BMI.
    4. Diet and chronic diseases are coming into focus.
    5. In a deep level, people know it’s not moral to eat animals. So strong justification is needed.

    Considering all that, it’s not a surprise that vegan diets are a target.

  7. Vincent Berraud July 20, 2016 at 3:30 am - Reply

    Have you had a response from the people at SBM following this article, Ginny?

    I am thankful that you wrote this. It is science based and reasonable, unlike the pseudo-skeptic piece it criticizes.

    Science Based Medicine owe it to themselves and to their readers to publish an apology and an adequate piece on veganism.

    • Ginny Messina August 20, 2016 at 2:31 pm - Reply

      Vincent, I have had not had a response yet, but am planning to contact them further about this. Stay tuned!

    • Jean Keller August 24, 2016 at 9:52 am - Reply

      Yes, science is very important when it comes to choosing a non-traditional diet like veganism that hasn’t been validated over generations of time and evidence. Whatever one’s dietary choice, we ALL need to keep up on new nutrition research, which is constantly evolving. It’s a very exciting field actually. For instance, taurine, labeled by Ginny in her above article as not being a key nutrient (or nutrient at all), has been traditionally know as a conditionally essential amino acid; however, the latest research reveals that this animal-based food is emerging as a functional nutrient as well, i.e. it helps to create a well nourished body and protect against diseases. That’s why it’s now being put in infant formulas. Research also shows benefits for metabolic, cardiovascular, and neurologic health. As a study on taurine concludes: “Absence from the diet of a conditionally essential nutrient does not produce immediate deficiency disease but, in the long term, can cause problems.” Yet many vegans are unaware of taurine (I didn’t know much about it until this book came along) and have no idea they should be supplementing because you don’t get taurine from plants. Vegans do have decreased plasma taurine levels compared to meat eaters, research shows. That’s why books like this can actually help vegans learn how to get healthier, whether they return to an omnivore’s diet that naturally supplies nutrients like taurine or choose to remain a vegan and supplement, presumably for the rest of their lives.

      • Simin September 6, 2016 at 1:51 pm - Reply

        Jean, I think those studies are a bit cherry picked. If a low taurine diet increases risk of diabetes then why is a vegan diet associated with a 60% lower risk of diabetes? Why do interventional studies show vegan diets, or diets that replace animal protein with plant protein improve glycemic control?

        As for what you say about risk, I think your assessment of risk is a bit unbalanced. Just because animal product diets have been around for a long time does not mean they don’t contain risks, indeed we can’t even fully assess the risks of an animal product diet without comparisons to a vegan diet. Furthermore, we know that animal products contain things which mechanistically are harmful, such as TMAO, heterocyclic amines, saturated fat, and even haem( which can increase ROS) We know that these things are associated with disease, as you say more plant based diets are healthier than high animal product diets, but we don’t know how much consumption of animal products is safe until one makes a comparison with vegan diets.

        • Phil July 23, 2017 at 6:17 am - Reply

          We all know that low GI foods protect against diabetes. So if one eats your vegan diet each day but also eats chicken with lunch and fish with dinner but eats all of the exact same daily foods – will they get diabetes? No. Because they eat low gi food and a high fiber diet. It is not eating meat that is unhealthy as most vegan researchers imprudently incorrectly extrapolate – it is eating high amounts of processed foods and not making health conscious decisions such as bigh fiber low gi carbs and lean cuts of meat or healthy fats. Go vegan because you care about the environment and animals welfare. Not because it is “more healthy” because it isn’t. It is less balanced and is missing key nutrients that the vegan community disregards and ignores to back their claims of the health benefits of going vegan, which are in fact quite detrimental to health.

          If vegans were to take their exact diet and incorporate a small portion of meat once a day they would be a lot better off healthwise. Moderation truly is the key to health when it comes to diet.

  8. Tiffany July 28, 2016 at 9:24 am - Reply

    So I’ve been looking for vegan & gluten free gummies for my kids. I found this brand and was wondering if anyone has tried them out?

  9. Gregory Stacey August 2, 2016 at 12:01 pm - Reply

    From the article…

    “Our food choices involve ethics, no doubt about that, but trying to impose a single moral code of eating on all people is profoundly unethical. In following a well-planned vegan diet, an unknown percentage of us will suffer, our health and quality of life. Surely the compassion that lies at the heart of ethical veganism extends to human animals.”

    My brain….
    Sure, it’s unethical to impose a single moral code on all people…The Constitution, the judicial system and imprisonment for crimes, intolerance of racism??? Humans are already suffering from chronic disease, lack of morality, and self centeredness. Also, how about you don’t “impose” a knife into a living beings throat. Surely that’s more offensive than a “moral code”.

    Also from the article…

    “Consider the field mice, pheasants, snakes and tender young rabbits—all of the innocent wild beings diced and sliced by the tiller that prepares the soil for your favorite grains.”

    My brain…
    Tu quoque logical fallacy. So silly it doesn’t warrant a response. Smiling ear to ear.

    • Jean Keller August 20, 2016 at 1:54 pm - Reply

      Gregory, you have failed to address the ethical question of long-time suffering vegans who are doing the diet “right” in every way. You describe yourself as a compassionate being but it’s obvious you have no compassion for these people. Please read my response to Sher, below, re obsessive-compulsive behavior. I thank you in advance for your open-mindedness and ability to look at your belief system in a new light.

  10. Sher Roo August 6, 2016 at 10:06 pm - Reply

    This is a good article, and I agree with you that vegan diets are not the ONLY way to eat. I follow a plant-based diet. But I can’t call myself vegan or even vegetarian, because although I eat totally plant-based, I allow myself incidental by-products like chicken broth in an otherwise all vegetable soup, or egg whites in otherwise vegan Costco Chipotle veggie brugers, or gelatin in vitamins/supplements. But if you cut out those by-products, you could call me vegan

    I just find it easier to eat this way, since I have an obsessive-compulsive personality to begin with. It takes away a lot of stress, not to worry about every little thing, and I still feel that I’m helping the planet and the animals.

    Thanks for having such an open mind. I love your Facebook page.

  11. Jean Keller August 20, 2016 at 1:30 pm - Reply

    I actually read this book, and the content in this blog reveals that nobody else did. As an ex-veg it was just really good to know I’m not alone, that many others also suffered on this diet. The book provides abundant testimony from not only vegans and ex-vegans but respected researchers, nutritionists, even a well-known pro-vegan MD who testifies that his long-term vegan clients with declining health were taking supplements and doing everything right, “calling into question the nutritional adequacy of a plants-only diet for whole populations.”

    That’s why I appreciate Sher’s comments about flexibility vs. obsessive-compulsive. A plant-based diet has been proven over many centuries to confer good health (best example: the Med Diet, which includes fish) but a plants-only diet has not. As the book points out, the vegan diet is too new in any significant numbers to know life-long health results. It sounds like Dr. Hall justifiably noted this in her review: the science is not there. Why you are chastising her for stating this, I don’t understand.

    • Ginny Messina August 20, 2016 at 2:30 pm - Reply

      Jean, I chastised her because she said the nutrition information in this book is evidence-based and it’s not. I just finished reading the book, too, Whether your own anecdotal experience matches hers isn’t relevant to the point that I was making–which is that the author of this book makes statements about nutrition and research that aren’t true.

      • Jean Keller August 24, 2016 at 8:12 am - Reply

        Actually, Ginny, I was impressed with the author’s sources for her nutrition information: a load of studies and research from some of the best nutrition journals out there, like JAMA. That’s why I respected the insights and conclusions offered. Even more convincing to me personally, I must admit, was the abundance of personal testimony from ex-vegans and their doctors, how their health and lives fell apart on this restricted diet although they did it “right.” This testimony isn’t science of course, but it sure is real to these people. You have to admit this is a non-historical diet that is just now being followed in any kind of significant numbers. We won’t know the health results for a couple of generations. It’s a risky diet in that way and I think that was the author’s main point, and a valid one.

        • Nicole Shintani November 1, 2016 at 11:04 pm - Reply

          honestly, I have never met a vegan who was doing it ‘right’ who suffered for it. and doctors themselves are highly uneducated in nutrition considering that the vast majority of doctors doing even get the minimum reccommeded hours of nutrition education. My dad is a doctor who advocates a plant based diet – he is not the main doctor for any of his patients but many of them state their usual doctors are filled with disbelief and amazement when they improve because of their diet, not understanding how they are doing so well. Far, far more people are suffering from a diet that contains animal products, and compassion should be extended to them as well.

          additionally what you say is merely anecdotes and not study based. Even my anecdote is relatively meaningless but it goes to show that doctors rarely have a good understanding of nutrition.

          My dad had to specifically gain a nutrition degree in order to get a decent education in nutrition.

  12. Duncan September 29, 2016 at 2:36 am - Reply

    Harriet Hall has a long history of going distinctly non-scientific when criticizing vegans – starting from the time she actually linked to Weston Price and Denise Minger as reliable rebuttals to The China Study (really!!). she even defended it when lots of her own site regulars warned her how utterly biased they were in the case of WPF.

    And she was a lot more easy going on Gary Taubes (with a few caveats) when reviewing the litany of distortions that was his book.

    Can’t see SBM as reliable when it comes to accurate nutrition info/reviews.

  13. Leslie Caza November 19, 2016 at 4:56 pm - Reply

    I am a 57-year-old woman who has been 99% plant based for close to 30 years (may get a bit of egg or milk hidden in some potluck-style meals). I wish they could see my last complete blood count results. I’m in excellent health. Also, Kaiser Permanente has encouraged their doctors to advice patients to go plant-based and has published an excellent starter booklet:

    Their document for providers is:

    “Founded in 1945, Kaiser Permanente is one of the nation’s largest not-for-profit health plans, serving more than 10.6 million members, with headquarters in Oakland, California. It comprises: Kaiser Foundation Hospitals and their subsidiaries. Kaiser Foundation Health Plan, Inc.” (Google it)

    The ones who pay the bills are the ones most likely concerned with the clients having excellent health! 😉

  14. […] take a peek at my new article on the Science Based Medicine website. You may recall that I criticized the website back in July for their review of the book Vegan Betrayal. I hadn’t actually read the book at the […]

  15. Margarita January 11, 2017 at 2:53 am - Reply

    Well said. Thanks a lot for this insightful post.

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