Dr. Michael Greger is up to his foils again!
He had some very interesting videos on phytates and cancer recently (start here).
But even more exciting, Dr. Greger just posted the first episode from his Latest in Clinical Nutrition: Volume 18 DVD – Blood Type Diet Debunked. In it, he discusses a paper from the Journal of the Norwegian Medical Association which I had not previously been aware of when writing my posts on the blood type diet.
And even if Dr. G didn’t have anything new, let’s face it, it’s just fun to debunk that diet!
Vegetarian Nutrition: What Does the Science Say?
– a presentation by Jack Norris, RD
Wed May 7, 2014
7:30 – 9:30 pm
First United Methodist Church
Community Center room
Corner of 12th and Jackson near OSU
Talk is free.
2.0 hours of CPE are available for RDs/DTRs for $25.
From a reader:
“[A]fter explaining [vitamin B12 and vegans] to my doctor, she read up on this, and in the past few months, has helped multiple vegan patients with vague neurological symptoms but normal serum B12! She now recommends MMA testing to her vegan patients, and would never have found their problems without it.”
As I hope most of my readers know, I do not quickly dismiss a study just because I don’t like the results.
In 2007, when EPIC-Oxford found a higher risk of fractures among vegans who didn’t get over 525 mg of calcium day, rather than finding some limitation of the study which is always possible to do, I started emphasizing that vegans need to get more than 525 mg of calcium per day. There are many other examples.
So when I say a study whose results I don’t like is pretty much useless, it’s because the study is pretty much useless and not because I don’t like the results.
In December 2013, a cross-sectional study from Austria aiming to compare the health status of vegetarians to other diet groups was released (1), and I wrote about it in the post Austrian Vegetarians: Good News? It was, with all due respect to the researchers, one of the most oddly designed studies I have seen to describe vegetarians.
In the study, the diet categories were:
– Vegetarian (vegans, lacto-ovo-vegetarians, and pesco-vegetarians)
– Carnivorous diet rich in fruits and vegetables
– Carnivorous diet less rich in meat
– Carnivorous diet rich in meat
The researchers didn’t define these categories for the participants when they were asking them which category they belonged to.
The researchers also created a number of health indicators that I didn’t feel confident in even though they concluded that vegetarians had the best self-rated health and the lowest incidence of chronic conditions.
Then on February 7 2014, another paper from this same study was published (2). I read the abstract and saw that their conclusions were somewhat different in the more recent paper, and less favorable to vegetarians, but given the boondoggle that I considered the study to be, I put it aside with no intention of doing another write-up.
Fast forward to April 1, when an article about the February paper was published on CBSlocal.com (Atlanta), Study: Vegetarians Less Healthy, Lower Quality Of Life Than Meat-Eaters. This CBSlocal article made the rounds quickly and so I decided it was time to comment on the study.
My criticisms of the February paper are pretty much the same as for the one from December. However, the February paper had more information.
With the diet categories so poorly designed, it’s surprising that they found a number of statistically significant differences in disease incidence between the groups. In comparing the vegetarian group to the carnivorous diet rich in meat group, the vegetarians had a higher rate of allergies, cancer, and mental illness, while the rich meat group had a higher rate of urinary incontinence. Asthma, diabetes, cataracts, hypertension, heart attack, stroke, osteoporosis, among other diseases, were not significantly different across diet groups.
As for the self-reported quality of life scores, some of the information didn’t match between the two papers; for example, the December paper lists the chronic conditions score for vegetarians as 1.45 while the February version lists it as 1.29 (lower is worse), a meaningful difference in their scheme.
Enough said about the specifics of this study, other than that the February paper is available for free at the link from the citation below, so if you want to check it out on your own you can. But quibbling over the details of either of these papers is fairly pointless. As the authors state in their relatively long section on the limitations of their study (2):
“Potential limitations of our results are due to the fact that the survey was based on cross-sectional data. Therefore, no statements can be made whether the poorer health in vegetarians in our study is caused by their dietary habit or if they consume this form of diet due to their poorer health status.”
They also bring up my earlier criticism:
“Further limitations include the measurement of dietary habits as a self-reported variable and the fact that subjects were asked how they would describe their eating behavior, without giving them a clear definition of the various dietary habit groups.”
The study from Austria, with all it’s limitations, is one thing. But the article from CBS Atlanta (link), adds insult to injury.
The CBS Atlanta article suggests that the Austrian study indicates causation (“But the vegetarian diet…carries elevated risks of cancer, allergies and mental health disorders”) and ignores a huge body of much better evidence regarding vegetarian diets, making it seem like this Austrian study is all we have to go on.
In fact, as most of my readers probably already know, much better studies following vegetarians over time have shown them to have equal or better health than regular meat-eaters in a number of diseases. You can read all about those studies in the VeganHealth.org section, Research on Vegetarians and Vegans.
For those not familiar with this research, I will point you to the fact that vegans have been found to have only a fraction of the risk of developing type 2 diabetes compared to regular meat-eaters (Type 2 Diabetes and the Vegan Diet).
1. Burkert NT, Freidl W, Großschädel F, Muckenhuber J, Stronegger WJ, Rásky E.
Nutrition and health: different forms of diet and their relationship with various
health parameters among Austrian adults. Wien Klin Wochenschr. 2014
Feb;126(3-4):113-118. Epub 2013 Dec 17. | link
2. Burkert NT, Muckenhuber J, Großschädl F, Rásky E, Freidl W. Nutrition and Health – The Association between Eating Behavior and Various Health Parameters: A Matched Sample Study. PLoS One. 2014 Feb 7;9(2):e88278. | link
For a long time, there has been a theory in mainstream nutrition that saturated fat causes the body to increase the production of cholesterol which, in turn, increases the risk of heart disease. This theory has not been without its detractors.
A large meta-analysis from the UK released this week caused quite a splash because it found that saturated fat was not significantly associated with heart disease (1). It wasn’t a complete surprise, as a 2010 meta-analysis of prospective observational studies had already produced similar findings (2).
The 2014 meta-analysis produced results for three different types of studies:
1. 32 prospective cohort studies analyzing self-reported dietary intake of fatty acids.
2. 19 prospective cohort studies analyzing blood levels of fatty acids.
3. 27 randomized, controlled trials of various fatty acid supplementation regimens.
The results were fairly consistent in that very few associations were statistically significant.
Among the cohort studies analyzing intakes, total saturated fat had a slight trend towards more cardiovascular disease. The only statistically significant finding was for trans fats increasing the risk of heart disease, while long chain omega-3s (EPA and DHA) were almost significantly associated with a lower risk.
Among the cohort studies looking at blood levels, total saturated fat again had a slight trend towards more cardiovascular disease. When looking at individual types of saturated fats, the common saturated fats found in animal products, palmitic acid and stearic acid, were more strongly associated with heart disease, though still not statistically significant.
Interestingly, the only fatty acids in the blood that were significantly associated with heart disease (all inversely) were margaric acid (a saturated fat found primarily in dairy products), the long chain omega-3 fatty acids (EPA, DPA, and DHA), and, more surprisingly, the long chain omega-6 fatty acid, arachidonic acid.
Arachidonic acid had previously been thought to be a cause of inflammation, and therefore heart disease (though other research has countered that idea, see Omega-6s: Not So Bad?).
In terms of clinical trials, only supplementation with omega-3s and omega-6s were analyzed and didn’t find any statistically significant associations, though EPA and DHA came close to being associated with a lower risk.
There were some errors in the version of the paper I have, but these errors did not alter the conclusion according to the attached notice.
So what should someone think about all of this?
One of my regular readers suggested that if you take a bunch of studies with measurement error and throw them all together, you shouldn’t be surprised that you don’t find anything. Perhaps – I don’t know enough about biostatistcs to be able to assess that sort of thing.
Here is what I believe: The primary saturated fats found in animal products, palmitic and stearic acid, most likely contribute to an increase in cholesterol and an increase in the risk of heart disease for people who have high cholesterol. But what is probably more important is not eating too many calories. Fiber is also probably as important as saturated fat, if not more so (3), because it can transport cholesterol out of your system.
Speaking of saturated fat, Dr. Michael Greger’s latest video on low-carb diets might be relevant, Low Carb Diets and Coronary Blood Flow.
1. Rajiv Chowdhury, Samantha Warnakula, Setor Kunutsor, Francesca Crowe, Heather A. Ward, Laura Johnson, Oscar H. Franco, Adam S. Butterworth, Nita G. Forouhi, Simon G. Thompson, Kay-Tee Khaw, Dariush Mozaffarian, John Danesh, Emanuele Di Angelantonio; Association of Dietary, Circulating, and Supplement Fatty Acids With Coronary RiskA Systematic Review and Meta-analysis. Annals of Internal Medicine. 2014 Mar;160(6):398-406. | link
2. Siri-Tarino PW, Sun Q, Hu FB, Krauss RM. Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease. Am J Clin Nutr. 2010 Mar;91(3):535-46. | link
3. Threapleton DE, Greenwood DC, Evans CE, Cleghorn CL, Nykjaer C, Woodhead C, Cade JE, Gale CP, Burley VJ. Dietary fibre intake and risk of cardiovascular disease: systematic review and meta-analysis. BMJ. 2013 Dec 19;347:f6879. doi: 10.1136/bmj.f6879. | link
Researchers from Japan recently published a meta-analysis of clinical trials and cross-sectional observational studies of a vegetarian diet and blood pressure (BP) (42). Many of these vegetarians were semi-vegetarians.
Among seven clinical trials, a vegetarian diet was found to reduce systolic and diastolic blood pressure by an average of 4.8 and 2.2 mm Hg, respectively. Among the 32 cross-sectional studies, vegetarians were found to have a lower systolic and diastolic blood pressure of 6.9 and 4.7 mm Hg respectively. These findings were statistically significant.
The authors said, “According to Whelton et al, a reduction in systolic BP of 5 mm Hg would be expected to result in a 7%, 9%, and 14% overall reduction in mortality due to all causes, coronary heart disease, and stroke, respectively….Obesity, excessive sodium intake, and excessive alcohol use are associated with increased BP and risk of hypertension; potassium intake and physical activity are associated with lower BP. In addition, intake of unsaturated fat, protein, magnesium, and dietary fiber may be associated with differences in BP.”
Interestingly, the only clinical trial that showed a vegetarian diet to increase blood pressure was the first PCRM pilot study using a vegan diet to treat type 2 diabetes (2). Diastolic blood pressure did decrease more in the control group, than the vegan group, in that study, while those on the vegan diet ended up with lower systolic blood pressure. However, two of the five subjects on the vegan diet who were on blood pressure medication discontinued their medication, while only one of four in the control group discontinued.
I have updated the Blood Pressure section of Disease Markers of Vegetarians
1. Yokoyama Y, Nishimura K, Barnard ND, Takegami M, Watanabe M, Sekikawa A, Okamura T, Miyamoto Y. Vegetarian Diets and Blood Pressure: A Meta-analysis. JAMA Intern Med. 2014 Feb 24. | link
2. Nicholson AS, Sklar M, Barnard ND, Gore S, Sullivan R, Browning S. Toward improved management of NIDDM: A randomized, controlled, pilot intervention using a lowfat, vegetarian diet. Prev Med. 1999 Aug;29(2):87-91. | link
Due to technical problems, I have changed systems through which posts are sent.
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Thank you for your patience!
I have finally finished researching vitamin K2 and heart disease. I've already published all of the research summaries in this blog, so I will not repeat them again here. However, if you would like to see all of them in one place, check out Vitamin K2 and Cardiovascular Disease at VeganHealth.org.
Here is a summary:
Preliminary evidence suggests that vitamin K2 could reduce the risk of heart disease, but the research is mixed and the positive findings come from only one country. More research is needed. If vitamin K2 reduces the risk of heart disease, it does not mean that eating animal products high in vitamin K2 will also reduce the risk, since animal products often contain other components that may increase the risk of heart disease more than vitamin K2 decreases it. Clinical trials are needed and, luckily, at least one is underway (1).
1. Kroon A. The Effects of Vitamin K2 Supplementation on the Progression of Coronary Artery Calcification. ClinicalTrials.gov NCT01002157. | link
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.
In doing my final search for studies on vitamin K2 and cardiovascular disease (CVD), I came across one on type 2 diabetes (1). Since diabetes can be fairly related to CVD, I decided to review it.
As with most of the studies on vitamin K2, the population was from The Netherlands. And just like the research on stroke, it was using the combined data from the Prospect and MORGEN arms of EPIC. After excluding people with prevalent diabetes at baseline, they had a study population of 38,094 men and women. The average daily intake of vitamin K2 was 49 µg in the highest one-fourth versus 15 µg in the lowest one-fourth.
After a median follow-up of 10.3 years, and adjusting for many variables (2), in comparing the highest intakes to the lowest, there was a trend towards a lower risk of diabetes, although the finding was not statistically significant (.80, .62–1.02). When looking at what effect an increase of 10 µg had on the risk of diabetes over the entire range of intakes, there was a borderline statistically significant beneficial association (.93, .87–1.00; p < .038).
The researchers had a number of guesses as to why vitamin K2 might be protective against diabetes, all of which amounted to an indirect effect on insulin sensitivity. They also pointed out that the fact that vitamin K2 comes from animal products might have hidden the true strength of a beneficial effect on type 2 diabetes.
1. Beulens JW, van der A DL, Grobbee DE, Sluijs I, Spijkerman AM, van der Schouw YT. Dietary phylloquinone and menaquinones intakes and risk of type 2 diabetes. Diabetes Care. 2010 Aug;33(8):1699-705. doi: 10.2337/dc09-2302. Epub 2010 Apr 27. | link
2. Variables adjusted for: age, sex, waist circumference, smoking status, physical activity, hypertension, education, alcohol consumption, total energy intake, saturated fat, polyunsaturated fat, monounsaturated fat, protein, fiber, calcium, vitamin C, and vitamin E.