"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.