Welcome to 2011! (Why don’t we have flying cars yet?) My new year’s blogolutions are to 1) write here more often and 2) actually answer emails. So far, I’m failing at both, but I’ve got 359 days left to clean up my act.
Sometimes, when I feel like I don’t have enough stress in my life and start craving a blood-pressure boost, I go to my old vegan haunts to read gems like these:
The only way meat can be digested is by putrefaction, our stomach acid is only 5% of that of a carnivore or omnivore so instead of being digested it basicly [sic] rots in your intestines which leaves toxic gases and waste to be absorbed into the blood. (From here.)
we know what’s happening. we’ve known for decades. however, we also have found that when we talk about the health detriments associated with eating the products of the corpse industries, people don’t believe us. (From here.)
[T]here is a single, sole cause to heart disease: cholesterol. If your total cholesterol is below 150 and LDL is below 70, you are essentially heart attack proof. What is the cause of high cholesterol? Saturated fat and animal products. (From here.)
Don’t you love this stuff? But I digress. What I want to talk about right now is one of the most oft-cited perks of being a vegetarian: an apparently lower risk of heart disease compared to omnivores. A recent paper called Chemistry Behind Vegetarianism sums it up by saying “Omnivores have a significantly higher cluster of cardiovascular risk factors compared with vegetarians, including increased body mass index, waist to hip ratio, blood pressure, plasma total cholesterol (TC), triacylglycerol and LDL-C levels, serum lipoprotein(a) concentration, plasma factor VII activity, ratios of TC/HDL-C, LDL-C/HDL-C and TAG/HDL-C, and serum ferritin levels.”
This is a trend that some folks translate as “meat causes heart disease”—a sentiment I saw plastered all over the veggie message boards during my most recent lurking spree. I assume this belief is bolstered by all the perfectly-preserved chunks bacon found in meat eaters’ arteries during heart biopsies.
Studies on vegetarians are inherently tricky. Although some folks dump animal foods strictly for ethical reasons, many of the meatless eat their veggies alongside other pro-health behaviors like exercising more, nixing tobacco, swapping refined grains for whole, limiting processed food (soy Frankenmeats notwithstanding), and avoiding the biggest of the baddies (trans fats, corn syrup, Cadbury Creme Eggs, and pretty much everything on this site).
What does all of that equal? Confounderville for researchers. It’s impossible to adjust for every little diet and lifestyle tweak a vegetarian makes in the name of health, so in scientific studies, vegetarians almost always have an advantage over health-indifferent omnivores. But the reason can’t be pegged on their meatlessness: Vegetarianism is a marker for a comprehensive shift in behaviors that influence disease risk.
But that’s not always the case with all groups of vegetarians. Studies focusing on some religious vegetarians (namely Buddhist and Hindu*) are more likely to show the effects of going meat-free in isolation rather than as part of a health-boosting plan. Confounding can still be an issue (especially in terms of stress reduction from certain religious practices)—but unlike the vegetarians who make a cascade of changes when they ditch meat, some religious vegetarians eat diets pretty similar to their omnivorous counterparts, just without flesh. That makes it a bit easier to compare apples with apples: We can see how an average omni diet stacks up against a similar diet sans meat, instead of comparing an average omni diet with a multifaceted vegetarian lifestyle.
*I’m excluding Seventh-day Adventists from the list because their diet and lifestyle recommendations involve much more than meat avoidance.
So where am I going with this? Right here. That’s the full text for a recent study from Taiwan looking at inflammatory markers in mostly-Buddhist vegetarians versus omnivores. (And if access to that link disappears, as full-texts are wont to do, just shoot me an email and I’ll send it to you.)
This study has a few good things going for it. For starters, it excludes smokers and uses only women—which automatically eliminates problems associated with controlling for tobacco use or gender-related differences in inflammatory markers. As the researchers note, the health-consciousness gap between Taiwanese vegetarians and Taiwanese omnivores is probably much smaller than with Western vegetarians and Western omnivores:
Most western vegetarians include fresh vegetables and fruits as their main source of nutrition and energy, based on health benefits of the foods. In contrast, most Taiwanese vegetarians choose a vegetarian diet because of their Buddhist religion, which teaches a policy of “no killing.” Buddhists in Taiwan have a dietary pattern similar to that of most Taiwanese in terms of meal patterns and cooking methods, except that they do not include any meat, fish, or poultry in their meals.
Although the researchers don’t explore the subject at all, the difference in religious practices between the vegetarians (apparently Buddhist) and omnivores (whose religion(s) weren’t documented) could be significant. Stress and mental outlook may play a role in the progression of heart disease, and meditation/centering practices associated with Buddhism could help improve both. If any of that is confounding the results, we won’t be able to know from the data presented.
But other than that, the study was pretty thorough. It tracked BMI, blood pressure, heart rate, glucose levels, cholesterol (total, HDL, and LDL), white blood cell count, homocysteine, and two inflammatory markers: lipoprotein-associated phospholipase AS (Lp-PLA2) and C-reactive protein (CRP).
The good news for the vegetarians is that their Lp-PLA2—a marker specifically for vascular inflammation—was lower than in the control group. But that’s where the good news ends. The researchers seemed pretty surprised to report that the vegetarians had higher levels of CRP (borderline significant at p=0.05) than the omnivores, along with higher homocysteine and triglycerides.
The original numbers are below. I highlighted the comparisons that weren’t so happy for the vegetarians. (Click to make it big, unless you’ve got really great vision.)
Interestingly, the researchers note that one of their earlier studies showed borderline lower CRP in vegetarians—but despite using it to claim vegetarians had a better risk profile than omnivores, that finding might not be very meaningful:
As we know, gender and smoking influenced the serum hs-CRP level significantly. In our previous study, there are more males and smokers in the omnivore group that can influence the statistical power of difference of hs-CRP between both groups. Actually, it failed to demonstrate a significant difference if male and female samples were analyzed separately.
In the current study, the researchers offer a few explanations as to why vegetarians might have higher CRP levels, even if their Lp-PLA2 levels were lower. One is that there were large variations in the CRP levels for all groups, which makes it harder to analyze statistically (translation: “maybe the correlation is a fluke”). They also mention that Taiwan vegetarians rely heavily on soy products as a substitute for meat, eat fewer fresh vegetables than western vegetarians, and typically cook vegetables in oil (presumably industrial seed oils).
The significance of this study is that it underscores the major issue with vegetarian research at large: The health-protective effects of vegetarianism are probably due to factors other than meat avoidance. When you study vegetarians that aren’t partaking in a bigger diet and lifestyle change, they no longer have a glowing health report. The lower Lp-PLA2 levels in this particular study are noteworthy, but higher CRP and triglycerides aren’t doing anyone any favors.
Of course, this isn’t the first study to poke holes the claim that meat-avoiders have special protection against heart disease. A 2005 study conducted in China rounded up some long-term vegetarians (6 to 40 years of meatlessness)—including many religious vegetarians—and compared their heart disease markers against an omnivorous control group. Apart from eating less saturated fat, protein, and cholesterol, the vegetarians had nutrient intakes similar to those of their omni friends.
The surprising results? The vegetarians had significantly thicker arterial walls (p<0.0001), reduced flow-mediated dilation (a predictor of cardiovascular events) (p<0.0001), higher blood pressure (p<0.05), and higher triglycerides (p<0.05) than the omnivores. (According to the paper, the raised blood pressure might be related to some popular high-sodium vegetarian foods such as processed protein food substitutes, fake oyster sauce, and tomato paste.)
In the researchers’ multivariate statistical models, vegetarianism had the strongest association with both artery thickness and diminished flow-mediated dilation out of all the variables documented—including age, gender, and triglyceride levels.
As might be expected, the vegetarians also had lower B12 levels and higher homocysteine than the control group—but even after adjusting for these, vegetarianism remained strongly linked with less-healthy hearts. The researchers concluded with this:
In summary, contrary to common belief, vegetarians, at least in the Chinese, might have accelerated atherosclerosis and abnormal arterial endothelial function, compared with omnivore control subjects. The increased risk could only be partially explained by their higher blood pressure, triglyceride, homocysteine, and lower vitamin B12 concentrations.
A little alarming, no? My guess is that these vegetarians got such a lousy report card because they didn’t make all the positive health changes most Western vegetarians make when they forgo flesh—but rather, replaced meat with processed foods, ate more carbohydrates and polyunsaturated plant fats, and failed to get enough B12 (resulting in higher homocysteine). This is what happens when you simply pluck meat out of your diet and fill the void with plant-based substitutes: the Healthy Vegetarian image becomes a lot less rosy.
No doubt some vegetarians would dismiss this study because the participants “did vegetarianism wrong” by not supplementing B12, not eating enough fruit and vegetables, consuming too much salt, and failing to provide daily offerings to the Arugula God. But if that’s the case, one could argue that all the meat eaters in the studies supporting vegetarianism just “did omnivorism wrong” for similar reasons. This is a good study because neither the vegetarians nor the omnivores seemed particularly health conscious. It’s rare that we get a level playing field like that.
Why vegetarian studies don’t study vegetarians
Much to the disgust of “real” vegetarians, a surprising number of folks who call themselves vegetarian are still feasting on flesh foods. The AJCN study “What to vegetarians in the United States eat?” gives a great rundown of this phenomenon. The paper starts out with an important observation about the state of vegetarian nutritional studies at the time it was written (2003), and these comments still apply to much of the literature we have today:
During the past 2 decades, studies have documented eating patterns and nutrient intakes of vegetarians in the United States. The studies, however, were conducted in volunteers and convenience samples recruited from relatively narrow geographic areas or from individuals belonging to a particular vegetarian orientation. Little is known about the eating patterns of a nationally representative sample of individuals who consider themselves to be vegetarians.
To tackle this problem, the researchers nabbed a bunch of nationally-representative data from a USDA food survey project, which documented the results of two 24-hour diet recalls as well as answers to the question “Do you consider yourself to be a vegetarian?” Then they looked in detail at what the vegetarians versus nonvegetarians were putting in their mouths. Out of the 13,000+ folks in the study, 334—or about 2.5 percent—identified themselves as vegetarian. That figure jibes with the numbers offered by the Vegetarian Resource Group and other polls that peg the percent at 2.5 to 2.8 or so.
But here’s the kicker. Out of those 334 so-called vegetarians, almost two thirds were still guzzling meat on their diet recall days. And we’re not just talking pesco-vegetarians eating fish, either: The fake vegetarians averaged 80 grams of red meat per day, not terribly far from the 137 grams reported by the omnivores with the highest meat intake.
Unfortunately, a lot of studies enrolling vegetarians take their subjects’ word about their diet habits, not realizing that fish, chicken, and Philly cheese steaks qualify as vegetables to some. That means that the vegetarian research we have—especially studies that recruit self-defined vegetarians for blood tests and other measurements—might not be examining the effects of a meat-free diet so much as a wishful-thinking diet. In this sense, studies looking at religious vegetarians (who have God to answer to) and ethical vegans (who have an ideology to answer to) are probably more legitimate than studies recruiting average Joe-Schmoes off the street who think being vegetarian means eating a salad on weekends.
But there’s more. This particular paper found some important differences between self-defined vegetarians and self-defined omnivores, regardless of whether the vegetarians ate meat or not—suggesting that the vegetarian label (and the lifestyle patterns it accompanies) is more important than the avoidance of meat:
- Both the vegetarians and the meat-eaters who thought they were vegetarians had lower BMIs than the self-defined omnivores.
- All of the self-defined vegetarians (meat-free or not) ate more total vegetables, more “other” vegetables, more total fruit, and more citrus than the omnivores.
- The self-defined vegetarians ate fewer white potatoes and fried potatoes than the most carnivorous omnivores. (My guess is the omnis were racking up some meat credits at McDonald’s, and did get fries with that.)
Of course, there are also some studies showing that, regardless of whether someone’s an omnivore in denial or embraces their flesh lust, eating more meat seems to correlate with certain cancers and heart disease. Does this “what do vegetarians eat” paper offer any insight into that? It sure does. If we compare the true vegetarians in this study (the ones who ate no meat on their recall days) with the true omnivores (the ones who ate plenty of meat on their recall days), we can see that the folks who limited their meat also consumed:
- More dark leafy greens, deep yellow vegetables, “other” vegetables, and total vegetables
- More whole-grain bread and brown rice (opposed to refined)
- More total fruit, citrus fruit, dried fruit, and “other” fruit
- More walnuts, almonds, and pecans
- More total legumes, lentils, garbanzo beans, and hummus
- Fewer beverages
- Fewer “sugars and candies”
- Fewer table fats
- More wine
- More carotene, vitamin E, vitamin C, thiamine, calcium, magnesium, copper, and dietary fiber
There’s nothing about eating meat that requires someone to inhale sugar and eat less fresh produce—but because meat (with all that awful saturated fat and cholesterol) has been so vilified in the nutrition world, the folks who eat more of it are likely to be less health-conscious than those who opt for the tofu slab. That’s why patterns like these emerge: Eating less meat goes hand-in-hand with other health-promoting choices, so we often see vegetarians trumping omnivorous control groups in terms of health markers.
Of course, with the paleo movement gaining force and more studies emerging on health-conscious meat eaters, it’s becoming obvious that not all omnivorous diets are created equal. The existing literature we have on paleo diets shows that folks can slash their risk factors for heart disease while still eating plenty of meat.
The B12/homocysteine/heart disease connection
If you’ll notice from some of the studies above, higher homocysteine (linked to B12 deficiency) is a common theme with vegetarians. Chronically elevated homocysteine may damage the lining of arteries and probably contribute to atherosclerosis—making this a major issue for vegetarians who either absorb B12 poorly or skimp on their supplements.
Unfortunately, not all veggie proponents got the memo. Dr. John McDougall, staunch believer in a meat-disease link, doesn’t seem to think B12 deficiency (and the ensuing elevated homocysteine) is anything to worry about:
…an otherwise healthy strict vegetarian’s risk of developing a disease from B12 deficiency by following a sensible diet is extremely rare—less than one chance in a million.
Take a moment to compare the possible consequences of your dietary decisions. You could choose to eat lots of B12-rich animal foods and avoid the one-in-a-million chance of developing a reversible anemia and/or even less common, damage to your nervous system. However, this decision puts you at a one-in-two chance of dying prematurely from a heart attack or stroke; a one-in-seven chance of breast cancer or a one-in-six chance of prostate cancer.
How many vegans have you met with B12 deficiency anemia or nervous system damage? I bet not one! Furthermore, you have never even heard of such a problem unless you have read the attention-seeking headlines of newspapers or medical journals.
That’s from a 2007 newsletter of his (probably my favorite blood-pressure-booster of all time). Did you catch his drift? B12 deficiency is just media hype. High homocysteine isn’t a problem compared to the artery-clogging havoc animal foods stir up. That wily New England Journal of Medicine is trying to compete with Cosmo and the National Enquirer by smearing the reputation of the meatless.
But just for kicks, let’s see what those sensationalist medical journals are trying to scare us with:
- Vitamin B12 deficiency is associated with coronary artery disease in an Indian population. “Also, vegetarians were found to have significantly lower vitamin B12 concentrations (p=0.0001) and higher incidence of [coronary artery disease] (p=0.01).”
- Vitamin B-12 and homocysteine status among vegetarians: a global perspective. “Overall, the studies we reviewed showed reduced mean vitamin B-12 status and elevated mean homocysteine concentrations in vegetarians, particularly among vegans. … Hyperhomocysteinemia is associated with an increased risk of atherosclerosis and cardiovascular disease.”
- Vitamin B12 and homocysteine status in asymptomatic Indian toddlers. “We studied the prevalence of V B(12) deficiency and hyperhomocysteinemia in 51 asymptomatic toddlers, from Pune, India. V B(12) levels were low and total serum homocysteine was high in 14% and homocysteine levels were significantly higher in boys. Programming for cardiovascular risk in adulthood possibly starts at a very young age through the homocysteine axis.”
- German vegan study: diet, life-style factors, and cardiovascular risk profile. “Although TC and LDL concentrations were favorable, low HDL and elevated homocysteine and Lp(a) concentrations were unfavorable. Overall, these results confirm the notion that a vegan diet is deficient in vitamin B(12), which may have an unfavorable effect on CHD risk.”
Quit with the fear mongering, medical journals!
Really though, I find it alarming that any educated vegan doctor is still sweeping the B12 issue under the (man-made-material) rug. Thanks to wonky claims about B12-associated problems being nearly impossible, some vegetarians and vegans are under the impression that high homocysteine isn’t anything to be concerned about, or that meat eaters are the ones who’ll succumb to its problems. In reality, this is probably one of the biggest threats to their animal-loving hearts.
Anyway, here’s the gist of this post:
Since so many vegetarian-versus-omnivore studies are comparing a complete lifestyle overhaul (health-savvy vegetarianism) with health indifference (standard “eat-whatever’s-there” omnivorism), it’s pretty hard to find a vegetarian study that can actually isolate the effects of meat. When a vegetarian’s main diet change is avoiding animal flesh rather than emphasizing fresh produce and moving away from refined foods, the health outcomes aren’t much different than those of standard omnivores (except for the added burden of higher homocysteine).
Just kidding. Three more things:
- Jimmy Moore kindly invited me back on his show for encore week. The interview is here, but he’s been having server problems and I’m not sure when that link will be working again. If it’s broken, just pretend I said something clever and carry on with your day.
- For any raw foodists in the house, I recently wrote an article for Frugivore Magazine about how to not ruin your teeth on a raw food diet. It’s a more up-to-date version of the dental posts I wrote last year on this blog.
- In case the grapevine didn’t reach your ears, January is gluten-free month. If you eat gluten-containing foods and are curious how you’d fare without them, now’s a good time for a little self-experimenting.
The real end. (Or is it?)