Alec Baldwin (actor); Neal Barnard (physician); Ed Begley, Jr. (actor); Patrick O. Brown (biochemist); Molly Cameron (Cyclist); Robert Cheeke (Professional bodybuilder); Chelsea Clinton (daughter of Bill Clinton); James Cromwell (actor); Mac Danzig (professional mixed martial arts fighter); Ellen DeGeneres (actress, comedienne, Talk-show host); Michael C. Dorf (Cornell law professor, author); William Clay Ford, Jr. (executive chairman of Ford Motor Company); Gary Francione (law professor, author); Michael Franti (Reggae artist); Brian Greene (scientist); Michael Greger (physician); Tonya Kay (dancer); Coretta Scott King (civil rights leader); Carl Lewis (track and field star); John Mackey (CEO, Whole Foods); Tobey Maguire (actor); Mike Mahler (body-builder); Brad Pitt (actor, producer); John Salley (professional NBA player); Alicia Silverstone (actress); Russell Simmons (entrepreneur); Salim Stoudamire (Professional NBA Player); Ruben Studdard (2nd season winner of American Idol); Mike Tyson (boxer); Jaci Velasquez (Contemporary Christian and pop singer); Alice Walker (Pulitzer prize winning author and feminist); Betty White (actress); Steve Wynn (entrepreneur); Mortimer Zuckerman (entrepreneur). (In a subsequent post, I hope to assemble a list of prominent Bostonians who are publicly vegan -- email your suggestions at jmcdonough@hsph.harvard.edu)

The essence of veganism is the avoidance of animal-based products in all aspects of our lives. I'm 99.5% there with food, and working on the rest. Regarding food, vegans try to avoid eating anything that has a mother: meat, poultry, fish, and all dairy products. (From many women, I commonly hear that "cheese" is the hardest item to imagine giving up. Eggs? They're like the bad boyfriend you thought you couldn't live without, and when he's finally gone, what a relief!)

Three reasons are key motivators for most who go vegan: first, revulsion at how animals are mistreated in our factory food system; second, distress about the documented adverse effect our factory food system has on the world environment, especially regarding climate change; and third, concern about the personal health effects of consuming animal products. Everyone has their own hierarchy of concerns; for my stepdaughter, Jax, it is the first; mine is the third. So how important to human health is it to stop completely consuming animals?

I teach U.S. health policy at the Harvard School of Public Health. Nutrition is not my beat, and I am not a nutritionist, and most certainly not a nutritional scientist. So keep that in mind as you read this. HSPH does have one of the most respected Nutrition Departments anywhere on the planet, let by the estimable Dr. Walt Willett who is also a great guy. You can read their scientific evidence-based recommendations here. They take lots of grief from the food industry for many of their conclusions, and avoid any external funding which could create the appearance of a conflict of interest.

If you look hard at the HSPH site, you won't find any significant reference to "vegan" or "vegetarian" (which is vegan without dropping dairy). That's because my HSPH colleagues, for the most part, are in the same place as folks as popular food writers Michael Pollan and Mark Bittman, the NYU nutrition researcher Marion Nestle, and others who advise, briefly, to treat meat as a condiment (meaning only small portions), to limit saturated fat intake to about 7% of your diet, to eat as much fruits, vegetable and whole grains as possible, and to eat fish.

So there are clear differences, though I am more drawn to similarities between the views of the 7%ers and those of vegans, rather than the differences. Here's why: both views emphasize a diet dominated by fruits, vegetables, legumes (beans, etc.), and whole grains. Both emphasize the need to either eliminate or minimize consumption of saturated and trans fats as well as processed and refined foods. Neither camp buys into one of the greatest con jobs in the history of food -- the assertion that milk is healthy for you (no moustache for me, thank you!). That's a lot of common ground.

But which side is right, or at least more right, based on science: the vegans or the 7%ers? I suggest that we don't know. Just about all of the scientifically-rigorous research I have seen compares one or the other of these dietary directions to the standard American daily diet which includes 20-30 percent or more saturated fat. I know of no rigorous research that has compared the vegan with the 7% diet -- perhaps a topic my HPSH colleagues might tackle, though I imagine there's not a lot of research funding available for this.

To bolster my assertion that we don't know, I refer to one of the modern day "bibles" of the scientific case for veganism, Colin Campbell's 2006 book, The China Study. One of the most dramatic parts of that book describes Campbell's 1970s research on rats and mice. He fed one group of mice/rats a diet composed 20% of casein (the essential protein ingredient in milk) and other groups only 5 or 6%. He injected all the rodents with cancer cells and then found consistent results showing huge cancer rates in the former group and miniscule or no cancer in the latter groups: "in the animals fed 5% protein, the dose-response curve completely disappeared." (p. 59).

So even for the most prominent researcher in the vegan camp, the evidence is not clear-cut versus the 7%ers. Does this mean there is no difference between the two approaches, and thus no reason to make the vegan choice? I would argue "no" for two reasons.

First, we need science-based evidence on the differences between these two positive nutritional paths, especially concerning the impact of a vegan diet on persons living with chronic diseases such as cardiovascular disease and type 2 diabetes (more on this in my next post). I believe both are positive nutritional choices for nearly everyone, and health improvements galore await most anyone who abandons the standard Western diet for either option. The question is whether vegans have an added advantage. And we need more evidence to know that.

Second, let's assume there is no compelling difference between the vegan and the 7% solution. Even if that were the case, there are two other compelling reasons to go whole grain/plant based. First, the way animals are treated in our factory food systems is barbaric and the only way most of us can deal with this reality is to ignore it. To face up to the appalling truth of how we treat billions of animals demands rejecting the system that makes it happen. And, happily, making that choice has never been easier.

The other reason is that this same factory food system is wrecking the world's environment. Livestock's Long Shadow, a 2006 report from the UN's Food and Agriculture Organization, documents that global livestock production accounts for one-fifth of all greenhouse gases, more than any other source, including transportation. That's just one of many examples of how our food system is killing us, not just one by one with unhealthy food products, but on a population basis through a growing environmental catastrophe.

These two points have nothing do to with the work of my colleagues at the HSPH nutrition department. Their role is to assess the scientific evidence of the impact of our food choices on human health. Were they to incorporate concerns about animal treatment and environmental damage to their judgments, they would delegitimize their crucial role as science-based advisors to everyone on nutrition and human health.

Me? I don't have that restriction. And neither do you.

(My next and final post in this first round on this topic -- our food choices and the U.S. health care system.)