"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."