Blog | Friday, August 11, 2017

The vegan argument

Can we say whether or not a well-balanced, vegan diet is BEST for human health? I will tell you the answer momentarily, but first- reasons for posing the question now.

A recently released documentary called What the Health reportedly makes the case for vegan diets, arguing that the attendant benefits are among the best-kept secrets of the medical-pharmaceutical complex. I say “reportedly,” because I have yet to see the film, although it is on my to-do list. A number of my friends and colleagues are featured.

The film came to my particular attention in a roundabout way. A video blogger with a MD degree and a sharp sense of humor, along with, apparently, a quite unprepossessing career in medicine- decided to assault the film for the entertainment of his social media followers. Colleagues of mine saw the critique, and gave as good- or better- than they got, in both video and print. References to, and remnants of the exchange made their way into my in-box. Rather like Mel Gibson's character in The Patriot, I felt obligated to enter the fray when the battle line rolled up to my front door.

Can we say whether or not a well-balanced, vegan diet is BEST for human health? No. But we can't say it isn't, either. And when other considerations are factored in- such as the ethical treatment of other species, and environmental impact- the arguments for well-practiced veganism are extremely compelling.

Why can't we say, for sure, that an optimized vegan diet is the single best choice for human health? Quite simply, the study required to prove that has not been done, and almost certainly never will be, because it is well-nigh impossible to conduct.

To prove that any one, specific diet is truly “THE best” requires comparing it to all other diets that are valid contenders. In this case, that could reasonably include, at a minimum, comparably optimal representations of Mediterranean, vegetarian, pescatarian, and flexitarian diets. Randomization should ideally happen at birth, or even in utero, and the outcomes that prove a diet is best- the combination of longevity, and lifelong vitality- require that the study run for entire lifetimes.

Because the comparison is among diets that are all optimized, and because other health practices would have to be standardized and comparable across groups, those lifetimes would likely be rather long, and the between-group differences small. Imagine, for instance, conducting a study intended to show the differential effects on longevity and vitality of running 35 miles a week, versus 32 miles a week. There might well be a dose-response effect ensuing, but it would be very small in the mix of factors influencing health over a lifetime, and hard to spot. When outcomes are small and hard to spot, sample sizes need to be very large to magnify them, and make them visible.

Our diet study has this same liability. So, it would require a vast sample of people (and/or their pregnant mothers) willing to be randomized to a specific diet for a lifetime. It would then require adherence to the assignment for that entire lifetime, and routine measures to confirm it. The investigators involved in launching the study would need a mechanism to pass it along to successors, since they would all die of old age before the study is done. I trust at this point I need not say more about why such a study has never been conducted, and is more than a little unlikely.

At one extreme, then, the claim that veganism is established to be the single, best diet for human health is somewhat exaggerated. Relevant evidence cannot correctly be said to be more than “suggestive.” From my perspective, having reviewed the relevant evidence with as much renunciation of a priori bias as humans can hope to achieve- both for a commissioned peer-reviewed paper, and a textbook- there is nearly comparable suggestive evidence for several variants on the theme of wholesome foods, predominantly plants, in time-honored and sensible combinations. I have heard my more ardent, vegan colleagues claim that wild salmon is toxic food for people. I am aware of no epidemiological evidence to substantiate that claim, but I would readily accept their argument that being eaten is certainly toxic to the fish.

At the other extreme is the argument one tends to hear when veganism is being disparaged and ridiculed, generally by those who simply like bacon and baloney, or -more ominously- by those trying to sell you one or the other, that we “need” meat to be strong and healthy. This claim figures among the baloney.

What animals need to be big and strong is not foods that resemble the muscles they are hoping to grow; that is simple-minded mythology, perhaps aided and abetted by the beef industry. They simply need foods to which they are adapted. The mightiest muscles of any land animal, those of the elephant, are produced entirely on a diet of plants. The mightiest muscles in the sea- those of the blue whale- are produced on a diet of tiny animals, krill and copepods. Lions build their muscles from meat; gorillas all but entirely from plants, and horses from plants exclusively. The greatest of human muscles is inconsequential as compared to any of these.

Some species are obligate herbivores, and some others are obligate carnivores; neither has a choice about how to grow their muscles, because choice is constrained by their anatomy, physiology, and underlying adaptations. We humans are decisively omnivorous, meaning it's a matter of choice. We can grow our muscle, and even fuel world-class athletic prowess, with plant or animal foods. Any argument that meat is necessary is simply misguided, uninformed, and ignorant. Among factors that matter in the determination of human muscle mass, strength, fitness, and performance- meat is moot.

Thus fail the arguments at the extremes in either direction, from my perspective. But let's be clear that arguments for vegan diets at a time of climate change, drying aquifers, industrial farming, assaults on biodiversity, rampant chronic disease, and global population pressures are anything but moot.

Consider, for example, just these two facts. A study out of Harvard, published in 2010, compared various sources of protein in the diet with regard to cardiovascular disease in over 80,000 women. The single, greatest beneficial effect observed derived from the displacement of beef in the diet, by beans. A study out of Loma Linda University, published in May of 2017, projects that the routine substitution of beans for beef by Americans- independent of any other climate control strategy- could achieve over 50% of the greenhouse gas emission reductions targeted for 2020 in the Paris Accord we have since decided to abandon.

Just those two facts make for a formidable argument on their own: humans can choose to grow their muscles out of beans, or beef, and beans are almost certainly, massively better for the health of humans, and the planet, alike. Mic drop.

But, actually, there are reasons to keep talking.

Beans are a staple in the diets of the world's longest-lived, most vital peoples, among the more salient of themes running through the world's Blue Zones. While absence of evidence on behalf of other diets is not reliable evidence of absence, the fact is that only vegan and near-vegan diets have been shown to shrink atherosclerotic plaque; reduce LDL as effectively as statins; and modify gene expression in a manner suggesting the potential to prevent the development and progression of cancer. Maybe other diets can do all this- but the burden is on them to prove it.

There are also the dire ethical implications of animal food, mass-produced. The only way anyone who has ever loved a dog can think of bacon as the casual, fun garnish into which our culture has turned it is either willful hypocrisy- or this. Pigs are highly intelligent, often claimed to be more intelligent than dogs; are sociable and can form bonds with humans just like dogs; and are routinely slaughtered in callous cruelty to embellish our cheeseburgers.

Yes, it's true that vegans need to supplement vitamin B12. But so what? The argument that this requirement makes the dietary approach flawed or incomplete tosses out the baby for the sake of an inconsequential drop of bathwater, and fails the meanest test of parity.

These days, with marketing claims based on the gratuitous addition of vitamins to water, it's harder to avoid nutrient supplements than to acquire them. All routinely clothed, indoor-working, northern-living humans need to supplement vitamin D, one way or another. Most humans exposed to modern living, and certainly those exposed to the liabilities of mass-produced animal foods such as second-hand antibiotics, are apt to benefit from probiotics. Veganism obligates select supplementation little more than modern living does.

Can we say that a balanced vegan diet is the single, best option for human health? No, we can only say it is among the likely contenders. Can we say that veganism is compatible with the adaptations of our omnivorous species? Certainly yes. Can we say that it allows for peak performance and muscle mass? Certainly yes. Can we say that it reliably garners the votes of the climate, the pigs and all other animals, and the planet? Certainly yes.

Argue against veganism if you choose, but concede it is because you like- or are selling- cheese, or meat. Other arguments are mostly just so much baloney.

Editorial note: for those wanting to know, the author is not vegan, although he eats a diet of minimally processed foods, predominantly plants, and does not eat any mammals and most other animals for ethical reasons. He counts four 4-legged animals, three dogs and a horse, among his closest friends.

David L. Katz, MD, FACP, MPH, FACPM, is an internationally renowned authority on nutrition, weight management, and the prevention of chronic disease, and an internationally recognized leader in integrative medicine and patient-centered care. He is a board certified specialist in both Internal Medicine, and Preventive Medicine/Public Health, and Associate Professor (adjunct) in Public Health Practice at the Yale University School of Medicine. He is the Director and founder (1998) of Yale University's Prevention Research Center; Director and founder of the Integrative Medicine Center at Griffin Hospital (2000) in Derby, Conn.; founder and president of the non-profit Turn the Tide Foundation; and formerly the Director of Medical Studies in Public Health at the Yale School of Medicine for eight years. This post originally appeared on his blog at The Huffington Post.