"Let me be clear about this. A low carbohydrate diet is quackery," Dr. Neal Barnard told me over the phone. "It is popular, bad science, it’s a mistake, it’s a fad. At some point we have to stand back and look at evidence."
Note to self: Don't ask Dr. Neal Barnard about limiting your carb intake.
"You look at the people across the world who are the thinnest, the healthiest, and live the longest; they are not following anything remotely like a low-carb diet," he said. "Look at Japan. Japan has the longest-lived people. What is the dietary staple in Japan? They’re eating huge amounts of rice."
Based on the fact that Barnard is the author of 15 books extolling the life-prolonging virtues of plant-based diets, I should have seen that coming. Apparently I'm one of few people in health media not familiar with his work, and his very clear perspective. I heard about Barnard because today he and his colleagues published a meta-analysis in the prestigious Journal of the American Medical Association: Internal Medicine that confirmed a very promising health benefit of being a vegetarian: an enviably lower blood pressure than your omnivorous friends.
The publicist for an organization called the Physician's Committee on Responsible Medicine emailed me to ask if I'd like to talk with Barnard about the research, and I always do want to talk about food research, so I did. High blood pressure shortens lives and contributes to heart disease, kidney failure, dementia, and all sorts of bad things, so any reasonable dietary way to treat or prevent it is worth considering. We've known for years that vegetarianism and low blood pressure are bedfellows, but the reason for it hasn't been clear.
"We looked at every published study, so it’s really undeniably true," Barnard said at the outset of our conversation, in a manner that anticipated a denial I wasn't prepared to offer. "People who follow vegetarian diets, they’ve got substantially lower blood pressures. [The effect] is about half as strong as taking a medication."
In this case substantially means that when you look at all of the controlled research trials comparing any kind of vegetarian diet to an omnivorous diet, the average difference in systolic blood pressure (the top number in the standard "120 over 80" jive) is about five millimeters of mercury. In diastolic blood pressure decrease (the bottom number) the difference is two. Not nothing, but not earth-shattering.
There have been a number of blood pressure studies on vegetarian diets in recent years, most famously the U.S. National Institutes of Health's 2006 DASH (Dietary Approaches to Stop Hypertension) studies. DASH was inspired by observations that "individuals who consume a vegetarian diet have markedly lower blood pressures than do non-vegetarians." It ended up recommending a diet high in fruits and vegetables, nuts, and beans; though it did not tell us to go all-out vegetarian.
"What’s new here is that we were able to get a really good figure for an average blood pressure lowering effect," Barnard said. "Meta-analysis is the best kind of science we do. Rather than just picking one study or another to look at, you go after every study that has been published that weighs in on this question."
In addition to the seven controlled trials (where you bring in people and change their diets, then compare them with a control group eating everything), the researchers also reviewed 32 different observational studies. Those are less scientifically valid than controlled studies, but they showed even larger decreases in blood pressure between vegetarian and omnivorous diets (6.9 systolic, 4.7 diastolic).
"It’s not uncommon for us to see patients at our research center who come in and they’re taking four drugs for their blood pressure, and it’s still too high. So if a diet change can effectively lower blood pressure, or better still can prevent blood pressure problems, that’s great because it costs nothing, and all the side effects are ones that you want, like losing weight and lowering cholesterol."
The research center to which Barnard refers is that of Physicians Committee for Responsible Medicine (PCRM). Barnard is president. Founded in 1985, PCRM describes itself as an "independent nonprofit research and advocacy organization." The advocacy is for ethical human and animal experimentation. According to its website, PCRM "promote(s) alternatives to animal research and animal testing. We have worked to put a stop to gruesome experiments, such as the military’s cat-shooting studies, DEA narcotics experiments, and monkey self-mutilation projects."
"Neal is a good guy and does good work," Dr. David Katz, Director of Yale University's Prevention Research Center, told me, "but the name of the organization is entirely misleading. It is not about responsible medical practice. It is entirely and exclusively about promoting vegan eating. A laudable cause to be sure, but I prefer truth in advertising."
The PCRM research group has another academic article published this week that found that a meat-based diet increases one's risk of type-two diabetes and should be considered a risk factor. Barnard's anti-meat orientation became pretty clear as I talked more with him about today's study.
"One way of thinking about it is that a vegetarian diet lowers blood pressure," he said, "But I like to switch it around: A meat-based diet raises blood pressure. We now know that, like cigarettes, if a person is eating meat, that raises their risk of health problems."
Barnard's blood-pressure study did not distinguish one type of vegetarianism from another. I asked what he thought of eggs and milk, at this point expecting that they wouldn't be a good idea.
"A semi-vegetarian diet does help some. We might suspect that a vegan pattern is going to be the best simply because studies have shown that vegans are the thinnest," he said. "People who add cheese and eggs tend to be a little heavier, although they’re always thinner than the meat eaters. We have suspected that when people go vegan their blood pressures will be a little bit lower, but so far the data don’t really show that."
Weight gain aside, because that is a different variable, why do vegetarians have lower blood pressure? "Many people will say it’s because a plant-based diet is rich in potassium," Barnard said. "That seems to lower blood pressure. However, I think there’s a more important factor: viscosity, how thick your blood is."
Eating saturated fat has been linked to viscous blood and risk for high blood pressure, according to the World Health Organization, as compared to polyunsaturated fats. Barnard paints an image of bacon grease in a pan that cools and solidifies into a waxy solid. "Animal fat in your bloodstream has the same effect," he says. "If you’re eating animal fat, your blood is actually thicker and has a hard time circulating. So the heart has to push harder to get the blood to flow. If you’re not eating meat, your blood viscosity drops and your blood pressure drops. We think that’s the more important reason."
Unprompted and seemingly apropos of nothing, we move into one of my favorite topics, Thanksgiving.
"You know how on Thanksgiving everyone kind of dozes off? People say it’s the tryptophan in the turkey, but it’s not. It’s all the gravy and the grease that’s entered their bloodstream. It reduces the amount of oxygen that’s getting to their brain and they just fall asleep."
"And what else could be affected by blood flow? One thing might be athletic performance. Take the fastest animals, take a stallion, they don’t eat meat or cheese, so their blood is not viscous at all. Their blood flows well. As you know a lot of the top endurance athletes are vegan. Scott Jurek is the most amazing ultra-distance runner in the world. That’s why Jurek says a plant-based diet is the only diet he’ll ever follow. Serena Williams is going vegan, too. A lot of endurance athletes are doing it. If you consider tennis an endurance sport."
"I do," I said. "It is." Venus and Serena Williams have been outspoken in their raw veganism for years. "Where should we be getting the protein to rebuild our muscles after a 100-mile run," I asked, "if there’s no meat on the table?"
"Well, the same place that a stallion or a bull or an elephant or a giraffe or a gorilla or any other vegan animal gets it. The most powerful animals eat plant-based diets. If you’re a human, you can eat grains, beans, and even green leafy vegetables. Broccoli doesn't want to brag, but it’s about one-third protein."
I can't speak for broccoli, but I do think the broccoli-growers association could consider that as a slogan. (Though, if you Google "Broccoli doesn't want to brag," it turns out Barnard said the same thing during an appearance on The Dr. Oz Show, so maybe he already owns it.) Broccoli does have one gram of protein per five-inch spear. That means 56 broccoli spears would get an adult man to the CDC's recommended daily protein allowance. For an ultra-marathoner it would be two or three times that.
"As for the findings [in this meta-analysis]," Katz told me, "they are valid, and show yet again that we could be eating far better than we do. The potentially misleading message is that veganism (or, more generally, vegetarianism) is the only way to eat to lower blood pressure."
The DASH diet studies showed that including dairy was more effective for lowering blood pressure than a strictly plant-based diet.
"That isn't an argument for dairy," Katz continued, "there are considerations other than blood pressure, of course. But it highlights the tendency for nutrition researchers with any given agenda to emphasize that portion of a larger truth in which they are personally invested. For what it's worth, Mediterranean diet studies also show blood pressure reduction."
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