My Debate with David Katz

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Recently I debated Dr. David Katz at the SoHo Forum. (Video is posted here.)

The resolution was: There is little or no rigorous evidence that vegetarian/vegan diets are healthier than diets that include meat, eggs, and dairy. 

I argued the affirmative (i.e., there is no rigorous evidence), and Katz argued the negative (i.e., there is rigorous evidence.) It was a somewhat topsy-turvy debate, because really, Katz was essentially arguing the affirmative (i.e., there is rigorous evidence) and thus, he should have gone first, so that my presentation could have been a critique to the evidence he put forth. Instead, I went first and had to predict what evidence he might present. Let’s agree, it wasn’t the best set-up as a debate. However, Katz and I both agreed to it many months in advance via multiple meticulous emails sent to us by the SoHo Forum director and moderator Gene Epstein. In my opinion, a professional person does not complain about something to which they’ve agreed. In his presentation, Katz went on at length displaying his published papers and books, presumably to make the case that he is a highly accomplished professional, yet he also spent many precious minutes protesting that the debate was unfair, that he’d been dealt a raw hand. Not very professional.

I feel OK about my performance although later thought of ways I could have argued more effectively. Here are a few things I wish I had observed and said in the moment:

To win the debate, Katz only had to show some rigorous evidence that a vegan/vegetarian is superior to other diets. In my view, 3-4 rigorous clinical trials would have been enough. Yet Katz did not do that.

Instead, he ran down the clock with diversionary tactics. Including:

    1. Complaining at length about how the debate resolution was stacked against him (see above);
    2. Talking about how he’d invited only one friend other than family members to the event, as if to make the point that he’d not brought along supporters (Clearly contradicted during the Q&A period when it became obvious that the questioners were nearly all Katz acolytes);
    3. Presenting a strawman junk-food vegan diet of milkshakes and hot-fudge sundaes–which we weren’t debating;
    4. Making the argument that low-quality evidence should be acceptable as high quality evidence  (i.e., the apple demo).

Why would Katz run down the clock? Because Katz had no real evidence to present. And in fact, he presented no rigorous evidence

Normally, at a scientific meeting, one shows a study, along with its conclusion, in a transparent way so that audience members can see it clearly. Katz did not do this. He presented an incomprehensible drive-thru blur of the data, the equivalent of taking a 200-page loose-leaf English paper to your teacher and dumping it in a disorderly pile at his or her feet, saying, ‘See? I’ve written a perfect paper.” To which the teacher replies, “How would I know? I have had no chance to read or examine it.”

This is, in effect, what Katz did. At 100 mph, he flashed through studies in which the conclusions were blotted out by a block quote. In the millisecond one had to look at the quote Katz had selected, one wondered: did it represent paper’s primary conclusion? No one could tell. It was impossible to evaluate the evidence he presented. This was, in effect, the presentation of zero evidence.

Katz kept apologizing that he had no time to go into depth with any of these studies, but let’s remember, he ran down the clock focusing on extraneous things. He did this to leave no time for the evidence, because he had no evidence.

Indeed, the one study that he singled out to show in detail–presumably the best evidence he could muster–was the highly flawed Ornish study, on only four dozen men with multifactorial interventions (not just diet), in which ultimately, two people died on the plant-based diet vs. one of the controls. This was his best, featured data. Not much, by  anyone’s standards (see a partial critique of the Ornish study here; a more complete critique is in my book).

The rest of the evidence that Katz included in his rapid-fire drive-by were a blur of observational studies, which–as I stated in the debate–have an only  0-20% chance of being accurate.

Update 6/10 A doctor has been fact-checking the trials that Katz presented and found that the majority do not represent what Katz said they did. Check out his work on Twitter @AmirWeiss1

Thus, in response to the resolution, There is little or no rigorous evidence that vegetarian/vegan diets are healthier than diets that include meat, eggs, and dairy, the answer must be YES, i.e., there is no rigorous evidence, or at least Katz presented none.

The outcome: Technically, Katz won, because his votes had a higher percentage increase, but in terms of the actual number of votes gained from those who were undecided, it was a tie. Afterwards, quite a few people said that they didn’t understand what they were voting for, since the YES (against the evidence) vs. NO (for the evidence) distinction was confusing to many. Gene Epstein, the event moderator, later commented, “Clearly the debate would have gone more smoothly if we had phrased the resolution positively–the confusion among voters could have been avoided.” He added, “It was a narrow win in which both sides picked up points. Katz was greatly helped by the fact that microphone was monopolized by his supporters. Real wins are characterized by differences of 20% or more, which was not the case here.”
A few other points:
  • Re: Lyons Diet Heart Study which Katz presented and to which I was asked to respond. We had different views. Katz was incorrect in insisting this was a multi-country study,  that took place across Europe and Africa. It was clearly a single-center study, in Lyons, France. However, I said it was mainly a study of a particular margarine when in fact it was a larger study of the “Mediterranean Diet.” I describe this trial accurately (at length) in my book but forgot in the moment on stage. In fact, the point I should have made about this and any other Mediterranean Diet study, is that they cannot be considered evidence for plant-based diets, because these Mediterranean diets are not low in animal foods. In fact, the largest, most famous Mediterranean Diet study, called PREDIMED, measured its Med diet study subjects (who apparently demonstrated improved cardiovascular benefits) eating nearly three times more red meat than is recommended by our government’s official guidelines (the Dietary Guidelines for Americans). Mediterranean diets also allow liberal amounts of cheese.
  • Surprisingly, Katz did not address or apologize for his ad hominem attacks on me (see below for the list). He has been written up in the Yale Daily News about this poor behavior, in an article that also revealed his link to Yale was “in name only,” without any substantive connections (Katz, for instance, does not teach at Yale, does not publish with Yale professors; he instead operates his center at a county hospital (“Griffin”), in Derby, CT, about 30 minutes from Yale)
  • Katz also did not respond to the issues of his many, many corporate conflicts of interest (COIs). See this post, on “David Katz, Junk Food’s Slyest Defender,” and additional COIs listed below. Instead, Katz defended his heavy investments in the plant-based diet industry by saying he was “just like Al Gore,” who had many millions invested in businesses that would profit from his arguments on climate change. Most principled people would disapprove of this, since having a profit motive for a certain policy inherently compromises one’s intellectual integrity. What if the science changes? Scientists tied down by financial incentives are less able to reckon honestly with any new information that might undermine their investments. Honest people abide instead by the time-honored principle that conflicts of interest and any possible improprieties should be avoided.


David Katz’s Ad Hominem Attacks (a selection, as cited in the debate):

“It matters that a journalist with a diet book to sell you… And did I mention she has a diet book to sell you?…. I don’t have a diet to sell.”   —David Katz, Huffington Post column, 5/5/14. Claims repeated 9/25/15 (Note: Katz is the author of 5-6 diet books, and my book is not a diet book.)

“The parasites of science who have no apparent interest in the weight of evidence, and instead feed selectively on studies… in close quarters with the fools and fanatics…They are a greater peril to us all”   David Katz, Huffington Post column, 10/1/15

“the cabal in question… including a band of wingnuts living in their mothers’ basements…David Katz, Huffington Post column, 10/23/15

“Nina is shockingly unprofessional … She is an animal unlike anything I’ve ever seen before.” —quoted in The Guardian  “The Sugar Conspiracy,” by Ian Leslie, April 7,. 2016 “Despite requests, he cited no examples of her unprofessional behaviour.’


David Katz’s Conflicts of Interest (as cited in the debate, only a partial list):

  • Plant-based diet ratings/digital companies
    • Nu-Val (now defunct), Katz was lead Science Advisor
    • Confidant, Inc  (mobile health applications for disease)
      • Katz is a member of the board
    • Better Therapeutics, Chief Science Officer
    • Diet ID: CEO and Founder, from Sept 2016 on.
  • According to his CV, here are some of the companies for whom Katz produced paid research or testimony:
    • Katz, as an expert witness, paid $3,500/hour to defend the high sugar-content of Chobani yogurt
    • Hershey: $731,000
    • Quaker Oats: $633,000 (and continued after PepsiCo’s acquisition of that company) 
        • Katz wrote a column promoting Quaker Oats and mentioned the brand in his book
    • Western Sugar Association—Katz was an expert witness (Law360)
    • KIND Bars paid Katz $154,000 to be a Scientific Advisor
        • Katz wrote a HuffPo column on KIND bars is quoted advising people to “add a low-sugar KIND bar” to their bag.
    • Walnut Industry paid Katz $1,109,945
        • Katz wrote two HuffPo columns promoting walnuts without disclosing this.

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