Ed. Note: After the prolonged comment thread in Harriet Hall’s review of this book in July, given the controversy, we were willing to consider a guest post offering another perspective. In this case, the perspective is very similar to Harriet’s, the main difference being primarily in emphasis.

As a dietitian working in the area of vegan nutrition, I see no shortage of outrageous claims about vegan diets. They come from both sides of the debate. Advocates for veganism sometimes ascribe unsubstantiated benefits to vegan diets while downplaying concerns about meeting nutrient needs.

On the other side of the debate are bloggers and authors who insist that a vegan diet is a dangerous choice and that it can’t support health over the long term. Prominent voices for this perspective include those whose health failed on a vegan diet and who eventually returned to eating meat, dairy and eggs. They are now on a mission to prove that humans require animal foods.

Mara J. Kahn is the latest author to try to capitalize on that story. Her book Vegan Betrayal has already been reviewed on Science Based Medicine and the nutrition information was deemed evidence-based. I came away with a different impression when I read the book.

I don’t feel any particular need to prove that a vegan diet is the only healthful way to eat; that’s not the point of veganism. The term was coined in 1944 by the founders of England’s Vegan Society and was defined as:

a philosophy and way of living which seeks to exclude — as far as is possible and practical — all forms of exploitation of, and cruelty to, animals for food, clothing or any other purpose.

So, a vegan diet doesn’t have to be the best; it just has to be as good as any other healthful way of eating. There are only two relevant questions: Can vegans meet needs for all nutrients? And do vegans suffer from nutrient deficiencies more often than omnivores?

And in fact, while she meanders off into a whole lot of tangential issues, Ms. Kahn says that answering these questions is the primary purpose of her book.

Vegans need good nutrition advice, just like everyone else

First things first. Being vegan can place you at risk for certain nutrient deficiencies. So can being a meat-eater. Kahn correctly notes that research has found deficiencies of iodine, iron, zinc, vitamins D and B12, selenium, calcium, and omega-3 fats in some vegans. According to NHANES data, Americans (most of whom are meat-eaters) are at risk for getting too little vitamin A, vitamin D, vitamin E, folate, vitamin C, calcium, potassium, magnesium and iron.

No matter what dietary pattern you follow, you need to pay attention to food choices to ensure adequate nutrient intake. The fact that some vegans and some meat eaters don’t meet all nutrient needs doesn’t say anything about the general safety of either eating pattern.

In fact, a whole lot of what Kahn addresses in her book has nothing to do with the safety of vegan diets. She says that a lot of vegans are eating in ways that undermine health because of bad advice on the internet. I agree. Most of my own work is devoted to countering harmful information aimed at vegans. But Kahn fails the logic test here. It doesn’t follow that vegan diets are risky, only that you should be careful about where you get your nutrition information.

And the irony of all this is that she doesn’t do a whole lot better with her own set of experts. They include a doctor who “knows nutrition inside and out” and who doesn’t consider beans, dairy or soy to be “authentic members of the top-quality protein category.” This is the same doctor who prescribes a homeopathic remedy for Kahn’s nerves. From here she gravitates to a medical intuitive and then finally to a couple of books published in 1952 and 1972 which have her convinced that some people can’t be vegan because of their “metabolic typing.” I’d say that Kahn’s round up of nutrition experts suggests that anyone, eating any kind of diet, can find bad nutrition advice.

Research versus headlines

There is a bit of a challenge in reviewing this book. While the author provides a long list of citations at the end of the book, she doesn’t always match them up with what she says in the text. Sometimes she’ll reference a study, sometimes she couldn’t be bothered. So, for example, unless you’re an expert on the role of termites in diets of African children (I’m not) you’ll just have to take her word for the fact that kids who eat termites have more beneficial gut flora and more “vigor” than European children who don’t eat bugs.

Except that once I got into this book, and saw how misleading most of her conclusions were, I didn’t want to take her word for anything. I wanted to know whether her larger point—that dietary variety is important and therefore vegans are at risk—was actually supported by this study. So I tracked down the research (1). It did indeed find a healthier gut environment among children in rural Burkina Faso compared to kids in Italy. But this was linked to a diet that the researchers said “consists mainly of cereals (millet grain, sorghum), legumes (black-eyed peas, called Niébé), and vegetables, so the content of carbohydrate, fiber and non-animal protein is very high.” The children in Italy were eating a “typical western diet high in animal protein, sugar, starch, and fat and low in fiber.”

Yes, the African children had more beneficial gut microflora but it was because their diet was mostly vegetarian, not because they ate an occasional termite. The study doesn’t support Kahn’s point; it counters it.

It’s just one of the ways in which she misuses data to bolster her position. But I doubt this was intentional. As I started poking around the book’s resources, I realized that Kahn most likely never looked at any research. She looked only at what reporters and bloggers were saying about the research. So I am guessing that her experience with this particular study (it doesn’t appear in her list of citations) was through an article in US News and World Report, which – it’s the media after all – played up the whole termite issue.

She doesn’t seem to be familiar with the research on any of the topics she addresses and it trips her up over and over again. Here’s another example. She suggests that soy isoflavones have not been shown to reduce menopausal hot flashes. Well, yes and no.

Placebo-controlled hot flash studies use one of two types of isoflavone supplements. When they utilize supplements that are derived from the whole soybean and that mimic the isoflavone profile of soybeans (that is, they are high in the isoflavone genistein) they are effective in reducing hot flashes (2). Supplements that are lower in genistein, and therefore very different from actual soyfoods, are far less effective. It’s a fine point, but a critical one in determining whether soyfoods affect hot flashes or not. A superficial glance at the research might suggest that they don’t. A more informed analysis tells a completely different story.

Anecdotes, observations and a little cherry picking

Kahn thinks most vegans are eating diets that are packed with carbs and too low in fat and protein. How does she know this? She’s seen it with her own eyes while having lunch at a Whole Foods café in Boulder, Colorado. By observing two “leggy” teens eating blue corn chips and coleslaw (which incidently, is not vegan) and a bored child “playing ring toss with her macaroni and cheese” (also not vegan) she concludes that vegans eat too many carbs. And while it’s possible that they balance their carb-heavy lunches with a protein-rich breakfast, Kahn says it’s unlikely because “breakfast for every veggie I’ve ever known is cereal or granola with a splash of soy or almond milk, often just a bagel with coffee or juice.”

I’ve never been to Whole Foods in Boulder, but I’ve looked at more than a few studies of vegan diets. Average fat intake among vegans is not particularly low; it’s about 30% of calories and average protein intake is moderate at 10 to 12% of calories (3-5).

Yes, vegans eat more carbohydrates than the average American. But the evidence suggests that this does not put them at risk for the insulin resistance that Kahn warns about (5, 6). In fact, among Seventh-day Adventists, vegans are far less likely to develop type-2 diabetes compared to meat eaters and lacto-ovo vegetarians (7).

Likewise, when Kahn cites studies on the triglyceride-elevating effects of high-carb, low-fat diets she completely ignores the more than a dozen studies showing that vegans typically have lower triglyceride levels compared with both meat eaters and lacto-ovo vegetarians (5, 8-10).

Sneaky paraphrasing

Lysine is the limiting amino acid in vegan diets, but Kahn uses some duplicitous misquoting to make it seem like a bigger problem than it is. She says: “Jack Norris, RD, himself a vegan, admits that it’s ‘very hard’ for vegans who don’t work out every day to meet daily lysine needs because they’re not consuming the calories needed to get enough from plants alone.”

Since I co-authored a book on vegan nutrition with Jack, I’m pretty familiar with his perspective on lysine. I know for a fact that he doesn’t believe it’s difficult to meet needs. Here is what he actually says about lysine [emphasis added]:

It is very hard to design a vegan diet that meets lysine requirements for a person who does not exercise daily without including legumes, seitan, quinoa, amaranth, pistachios, or pumpkin seeds

That is, it’s only difficult if you happen to eliminate a huge category of plant foods from your diet. Jack recommends (as do I) at least three servings per day of lysine-rich plant foods. Menu choices might include veggie burgers, hummus, bean burritos, quinoa, pumpkin seeds sprinkled into a salad, scrambled tofu, split pea soup, falafel, cereal with soymilk, or a peanut butter and jelly sandwich. There is nothing odd or onerous here. It is not particularly difficult to meet lysine needs on a vegan diet.

She read it on the internet

Like every other book aimed at discrediting veganism, Kahn has a chapter on soy. And, like every other soy detractor she claims that Asians eat very little of this food and that what they do eat is usually fermented. This comes straight from the internet. It couldn’t possibly come from the research, because it’s not at all what the research shows.

Studies published over the past 25 years have comprehensively quantified soy intake throughout Asia. The research shows that non-fermented foods like tofu and soymilk actually play a bigger role in Asian diets than fermented soy products. In fact, ethnic Chinese in China, Singapore and Hong Kong consume almost no fermented soy with the exception of soy sauce. Even in Japan where the fermented foods natto and miso are widely consumed, tofu accounts for about half of all soy intake. And depending upon the country and region in question, average soy intake ranges from one-half serving per day to about two servings per day (11).

Nor has soy intake been associated with lower testosterone levels in men as Kahn warns. That’s the internet again. Yes, a few case reports showed that men consuming excessive amounts of soy – 12 or more servings per day – experienced a reduction in testosterone levels. But the extensive clinical trial data, which includes more than 30 studies, show that soy doesn’t lower testosterone levels even when men consume the equivalent of six servings per day (12).

Soy is not the only dangerous plant food according to this book. There are pages of fearmongering about wheat which Kahn alleges is an opiate due to genetic modification of its protein gliadin. Never mind that there is no genetically modified wheat on the market. Or that the digestive product gliadorphin, which has been found to have opiate-like effects in lab animals, probably can’t even be absorbed by humans. Or that there is no evidence of addiction to or withdrawal from wheat.

“Carninutrients” and more

And then finally, there is this: “Science continues to discover essential micronutrients found solely in animal sourced food.”

If you’re familiar with the Weston A. Price Foundation, you know where she’s going with this. For those who don’t know, Dr. Price was a dentist who, in the 1930s, traveled the world and determined that not only “fine teeth,” but also “fine character” were related to nutrition. He wrote a book called Nutrition and Physical Degeneration in 1939, and it somehow gave rise to a movement that focuses on the benefits of butter, raw milk, and cod liver oil, and the harmfulness of vaccines, baking powder, and tofu.

Dr. Price suggested that there was an Activator X that improved mineral absorption, bone development, prevented tooth decay and protected against inflammation and cancer. His followers believe that this was vitamin K2 or menaquinone. According to Kahn, vitamin K2 deficiency is widespread in the American population. According to the Institute of Medicine we have no actual dietary requirement for vitamin K2 as long as we consume adequate vitamin K1. Nor are there any established requirements for the other compounds that Kahn believes are essential nutrients like carnosine, taurine, and conjugated linoleic acid.

When a vegan diet fails

The bottom line is that Mara Kahn was unable to maintain good health as a vegan. I can’t speculate as to why that is. I only know that her book fails to make the case against a vegan diet. She cobbles together misinformation from the internet and blends it with her own faulty interpretations of nutrition research. And then for good measure tosses in a whole lot of completely irrelevant observations about nutrition. It makes for a compelling read. But by no means does it prove anything about vegan diets.


  1. De Filippo C, Cavalieri D, Di Paola M, Ramazzotti M, Poullet JB, Massart S, Collini S, Pieraccini G, Lionetti P. Impact of diet in shaping gut microbiota revealed by a comparative study in children from Europe and rural Africa. Proc Natl Acad Sci U S A 2010;107:14691-6.
  2. Taku K, Melby MK, Kronenberg F, Kurzer MS, Messina M. Extracted or synthesized soybean isoflavones reduce menopausal hot flash frequency and severity: systematic review and meta-analysis of randomized controlled trials. Menopause. 2012;19:776-90.
  3. Spencer EA, Appleby PN, Davey GK, Key TJ. Diet and body mass index in 38000 EPIC-Oxford meat-eaters, fish-eaters, vegetarians and vegans. Int J Obes Relat Metab Disord 2003;27:728-34.
  4. Waldmann A, Koschizke JW, Leitzmann C, Hahn A. Dietary intakes and lifestyle factors of a vegan population in Germany: results from the German Vegan Study. Eur J Clin Nutr 2003;57:947-55.
  5. Goff LM, Bell JD, So PW, Dornhorst A, Frost GS. Veganism and its relationship with insulin resistance and intramyocellular lipid. Eur J Clin Nutr 2005;59:291-8.
  6. Waldmann A, Strohle A, Koschizke JW, Leitzmann C, Hahn A. Overall glycemic index and glycemic load of vegan diets in relation to plasma lipoproteins and triacylglycerols. Ann Nutr Metab 2007;51:335-44.
  7. Tonstad S, Stewart K, Oda K, Batech M, Herring RP, Fraser GE. Vegetarian diets and incidence of diabetes in the Adventist Health Study-2. Nutr Metab Cardiovasc Dis 2013;23:292-9.
  8. Bissoli L, Di Francesco V, Ballarin A, Mandragona R, Trespidi R, Brocco G, Caruso B, Bosello O, Zamboni M. Effect of vegetarian diet on homocysteine levels. Ann Nutr Metab 2002;46:73-9.
  9. De Biase SG, Fernandes SF, Gianini RJ, Duarte JL. Vegetarian diet and cholesterol and triglycerides levels. Arq Bras Cardiol 2007;88:35-9.
  10. Li D, Sinclair A, Mann N, Turner A, Ball M, Kelly F, Abedin L, Wilson A. The association of diet and thrombotic risk factors in healthy male vegetarians and meat-eaters. Eur J Clin Nutr 1999;53:612-9.
  11. Messina M, Nagata C, Wu AH. Estimated Asian adult soy protein and isoflavone intakes. Nutr Cancer 2006;55:1-12.
  12. Hamilton-Reeves JM, Vazquez G, Duval SJ, Phipps WR, Kurzer MS, Messina MJ. Clinical studies show no effects of soy protein or isoflavones on reproductive hormones in men: results of a meta analysis. Fertil Steril 2010; 94(3), 997-1007.

Virginia Messina, MPH, RD is a dietitian specializing in vegan nutrition. She’s an editor and advisor with organizations that produce educational materials for dietitians and consumers, and she shares evidence-based information on vegan diets through her website


Posted by Ginny Messina