Ginny Messina has written a response to Kris Gunnars of Authority Nutrition, Paleo Advocates Get Vegan Diets (and Saturated Fat) Wrong.
Previous research has shown that it takes at least 3.7 g of the short-chain omega-3 fatty acid, ALA, to increase DHA levels in vegetarians in the short term, with the longest trial lasting 6 weeks.
A new study from Loma Linda University (1) put a group of lacto-ovo vegetarians, average age of 38, on three different daily regimens for 8 weeks each:
– 1 oz of walnuts (3.0 g of ALA)
– 1 regular egg (110 mg DHA)
– 1 fortified egg (~500 mg DHA, 40 mg EPA, 1 g ALA)
The ratio of omega-6 to omega-3 was 6 to 1 in the walnut phase, which is relatively low for a vegetarian diet, but DHA levels did not increase. The ratio of total cholesterol to HDL was lower in the walnut treatment compared to both egg treatments and there were no significant differences for any inflammatory markers.
In conclusion, 8 weeks of 1 oz walnuts daily improved cholesterol markers but did not increase DHA levels.
I have updated Omega-3 Fatty Acid Recommendations for Vegetarians with this information.
1. Burns-Whitmore B, Haddad E, Sabaté J, Rajaram S. Effects of supplementing n-3 fatty acid enriched eggs and walnuts on cardiovascular disease risk markers in healthy free-living lacto-ovo-vegetarians: a randomized, crossover, free-living intervention study. Nutr J. 2014 Mar 27;13(1):29. | link
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
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