Response to Chris Kresser’s “Why You Should Think Twice About Vegetarian and Vegan Diets”

Chris Kresser is a licensed acupuncturist and practitioner of integrative medicine who promotes animal products as a way to optimal health.

Kresser recently wrote an article where he expresses his concern for the health of those considering vegetarianism: Why You Should Think Twice About Vegetarian and Vegan Diets.

I don’t think it is a terrible article – there are nutrients that vegetarians and vegans have to pay attention to in order to achieve optimal health and he hits on most of them. However, he makes it seem like all vegetarians or vegans are going to have problems with all of those nutrients, which is not the case.

Vitamin B12 is one example of his overblown concern. He emphasizes the myriad of problems that can occur from B12 deficiency, which are quite frightening. In fact, if you allow vitamin B12 deficiency to go on long enough, you’ll die – and along the way some pretty bad things are going to happen. But all you need to know is to take a supplement and you’ll likely have a better B12 status than your average omnivore.

I’m not going to go through every nutrient he mentions and point out what I think he got right and wrong – but you can check out any of them at VeganHealth.org.

Kresser asks, “But don’t vegetarians live longer than omnivores?” He answers, “While it’s true that some observational studies suggest that vegetarians and vegans enjoy longer lifespans, these studies were plagued by the ‘healthy user bias’.”

He goes on to explain that people with healthy lifestyle habits choose to be vegetarian and so the lower mortality of vegetarians can be explained simply by other lifestyle factors.

Kresser singles out the Health Food Shoppers (HFS) study as being the one study that has risen above healthy user bias, and points out that it showed vegetarians to be no better off than non-vegetarians.

In fact, the HFS study is one of the weakest study designs of all the cohort studies comparing mortality rates of vegetarians. In the 1996 paper on the HFS that Kresser cites, the authors state:

“Another limitation is that the questionnaire was short and did not include several important food groups (for example, dairy products, fish, alcoholic drinks), did not allow us to estimate energy intake, and did not include other factors known to be associated with health (exercise, socioeconomic status, past smoking habits). We were therefore unable to explore whether the significant associations observed were partly due to confounding by other dietary or non-dietary variables.”

In contrast, the Adventist Health Study-2, which produced the most recently published paper on vegetarian mortality, adjusted for smoking, exercise, income, education, alcohol, geographic region, and sleep. They found that vegans had a 15% lower rate of early death than non-vegetarians (this finding was not statistically significant, though very close).

Additionally, there are good reasons why a vegan diet might lead to lower mortality – much lower LDL cholesterol levels, body mass index, and hypertension. There is very strong evidence to suggest vegans have only a fraction of the risk of type 2 diabetes, partly due to plant iron being harder to absorb (link).

Kresser says, “Still, while it may be possible to obtain adequate nutrition on a vegetarian diet, it is not optimal – as the research above indicates.”

I will agree that meat-eating is the more convenient choice for getting some nutrients – though sometimes it’s an all too convenient way to get too many, such as in the case of iron, saturated fat, and cholesterol.

While we don’t yet know for certain if a vegan diet increases the chance of living longer, when you consider the dearth of studies showing that meat-eaters live longer than vegetarians, it seems like a jump to conclude that meat-eating is the “optimal” choice.

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8 Responses to “Response to Chris Kresser’s “Why You Should Think Twice About Vegetarian and Vegan Diets””

  1. Laura Says:

    I haven’t read the article yet, but was anything mentioned (or are there other studies out there) which mention the number of meat-eaters and vegetarians/vegans who are living on prescription medication and/or have had surgical interventions or other invasive medical treatments? Wondering if food intake is the only thing at play in regard to “the dearth of studies showing meat-eaters live longer…”

  2. Dan Says:

    “Chris Kresser is a licensed acupuncturist and practitioner of integrative medicine . . . ”

    Right there, I could have stopped listening to anything Chris Kresser has to say.

    While I am not as hard core as the skeptics on the website http://www.sciencebasedmedicine.org, I am not willing to listen to bogus dietary advice from a “licensed acupuncturist and practitioner of integrative medicine”. I would rather get my dietary advice from someone who is trained in evidence-based nutrition or evidence-based medicine (or both). Sorry if that sounds snobbish or snotty. Certainly many vegans are into new age and alternative “healing practices”, which is a shame, because there’s nothing to suggest that traditional, evidentiary medicine and vegan nutrition can’t be combined.

  3. Jack Norris RD Says:

    Laura,

    Included in the exclusion criteria for Adventist Health Study-2 (AHS-2) was a “history of a specific prior cancer diagnosis (except nonmelanoma skin cancers) or of cardiovascular disease (CVD) (coronary bypass, angioplasty/stent, carotid artery surgery, myocardial infarction, or stroke; or angina pectoris or congestive heart failure treated in the past 12 months).”

    In terms of taking medications, I normally don’t see results adjusted for that in studies of mortality.

    Interestingly AHS-2 found that vegans were less likely to get screened for prostate cancer:

    http://www.ncbi.nlm.nih.gov/pubmed/23833686

  4. richard mcmahan Says:

    I very much agree with Dan’s (well said) point of view. I take seriously those from the relevant sciences.

  5. Alex Says:

    Whether Chris is going too far or practicing certain pseudo-science to an extent is somewhat irrelevant, I don’t think his practice of acupuncture disqualifies him, especially considering the word “licensed is used”.

    Here’s a big problem, its not a balanced debate, vegans won’t eat meat but its not vice-versa, meat eaters will eat their veggies, wouldn’t a more balanced study compare meat eaters who eat hardly any veggies to vegans, even though vegans would never eat meat although hard-core meat eaters may still eat a veggie or two?

    Comparing a “Salad only diet” vs. a “salad and meat diet” rather than a “meat only diet” seems unfair.

  6. Ian Says:

    Alex: “a salad only diet”?! Who in this debate is eating a salad only diet?
    The appropriate comparison is surely between real world vegans and real world omnivores. Ideally the studies would involve large enough numbers of people with detailed and accurate enough data about diets that you could extract subsets for comparison, including ‘meat only’ eaters, but what would be the point? My guess is that you might find a fair number of people who eat large amounts of meat and not a whole lot else, but you’re not going to find too many genuinely ‘salad only’ people still standing, at least not if what you mean by the terms ‘salad’ and ‘only’ is what they are generally understood to mean.
    And how would the accusation of ‘pseudoscience’, if true, be irrelevant? It would surely be entirely relevant. A licensed acupuncturist need not have any more nutritional training than your average MD – which is to say: not a whole lot; and depending on the school the science-based (i.e. real world evidence based) nutritional teaching may not be great at all.

  7. Amy Says:

    Hi Jack, thanks for writing about this. I am a trained biologist (who has published peer-reviewed research) who is now studying nutrition and I am an ethical vegan as well. Naturally, vegan nutrition is something I spend most of my free time reading about, which is why I very much enjoy yours and Ginny’s scientific, unbiased work.

    I have not heard before that non-heme iron intake contributes to lower risk for DMII. I checked out the reference and read the paragraph in their conclusions that states:

    “Several possible mechanisms may explain the beneficial effects of a vegetarian diet [17]: higher intake of fibre [18], lower intake of saturated fat [and a higher polyunsaturated and saturated fatty acid (P/S) ratio] [19], higher intake of non-heme iron and reduction in iron stores [20], …..”

    This was frustrating since after reading the whole paper they didn’t actually comment on non-heme iron/reduction of iron stores except in that one sentence, providing me with no scientific study to back up the claim directly. But I figured ok, I just need to read their reference #20 that they are citing. So I looked up the paper on pub med and the link to the free full-text can be found here:

    http://ajcn.nutrition.org/content/51/2/301.long

    It’s a paper from 1990 about iron adaptation, and after scouring the whole thing I do not see the advantage of non-heme intake with DMII risk reduction mentioned. It is possible that I have missed it in one of these two references but I have read them twice.

    Anyway, the point of this long comment is: Is there a study that showed that non-heme intake and/or lower iron stores was correlated with a lower risk for DMII? If so, can you point me in the right direction? I have never heard of this and I’m very curious to read more about it. Thank you.

  8. Jack Norris RD Says:

    Hi Amy,

    See the section on Type II Diabetes here:

    http://veganhealth.org/articles/iron#chr

    If you want me to send you those studies cited, let me know.

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