The Canadian psychologist Jordan Peterson informed listeners of an interview he did recently that he eats only beef, salt, and water, and never cheats. His daughter Mikhaila started him on the regime. While Peterson was careful to stress that he was no dietary expert, and was speaking in a personal capacity, he credits the diet with helping him to lose 50 pounds. Not only that, he says, but he has gained muscle, successfully treated his sleep issues, fatigue, depression, digestion, snoring, and gum disease.

The only downside is that reintroduction of any other food or drink makes him sick; he cites a recent experience when cider produced an “overwhelming sense of impending doom” and prevented him from sleeping for 25 days.

Questioned on the need for vitamin C, Peterson pointed to a study saying that this essential nutrient is unnecessary if we don’t eat carbs. An evolutionary psychologist by training, he also references world cultures that he believes survived on meat alone. He offers speculative hypotheses for his sensitivity to any reintroduced food.

Joe Rogan, the comedian/commentator who conducted the interview in which Peterson’s dietary news was revealed, listens reverentially, compliments Peterson repeatedly on his physical appearance, and declares himself interested in trying the all-cow plan himself. He subsequently invites Mikhaila Peterson on the show to learn more about the diet she invented.

I want to take a moment to express genuine sympathy for what Mikhaila Peterson has been through. She’s had a lifetime of chronic illness and autoimmune disorders, including rheumatoid arthritis and severe depression. She had joint replacement surgery at the age of only 17. She’s spent most of her life on an intense cocktail of medications. I am in no way making light of this, and I can imagine that if I found myself suffering from similar illnesses, I too would want to believe that – science bedamned – I had found a miracle cure.

Ms Peterson talks about how she arrived at the beef-only regime through a process of elimination and reintroduction – essentially experimenting on herself. She claims that she has come off medication and is now in remission from severe arthritis, chronic fatigue, depression and many other symptoms. If you want to know more, there’s her blog, instructively entitled Don’t Eat That.

‘Prof Peterson says that he’s not recommending the diet, but asks Rogan in his customarily authoritative and irreverent tone, ‘why is everyone fat and stupid?’’ Photograph: Carlos Osorio/Toronto Star via Getty Images

The blog eschews the “I’m not an expert” tagline her father gives his Rogan interview. Rather, it proclaims: “many (if not most) health problems are treatable using diet.” It answers the question “should you start an elimination diet?” with a resounding yes for anyone experiencing symptoms from a list so ludicrously broad that it ends with “anything else I haven’t mentioned that really bothers you or if you feel like you could feel better.” The blog also affirms that there’s three more permitted comestibles on the Peterson plan, namely: vodka, bourbon and silver tequila.

Ms Peterson is offering consultations for $120 an hour. If that seems expensive, well, simply read the testimonials she has collected to assure you that it is money well spent. Do not stop to consider if the plural of anecdote is evidence.

Meeting criticism of her lack of qualifications, Ms Peterson says, “I’m not going to go to a school run by either the pharmaceutical companies or the food companies to learn about how eating grain is healthy.” Contemporary nutritional science is not, of course, infallible or immutable, but unlike Peterson’s beef and vodka diet, it has been arrived at over many decades through longitudinal and quantitative studies. There are schisms within the discourse – for example, over the risks of saturated fat. But such schisms are best addressed through systematic reviews of research and further peer-reviewed investigation.

Ms Peterson’s blog cherrypicks studies to support her beliefs, while treating robust scientific literature and consensus on nutrition with the kind of scorn for the scientific method that I ordinarily associate with anti-vaxxers, raw-food-cures-cancer advocates, or the eminently disturbing bleach enemas for autistic children crowd.

How can we explain the health improvements the Petersons claim to be experiencing? There is, probably, the attribution of causation to correlation. You eat a little broccoli. You experience a month-long sensation of impending doom. The broccoli caused it. Another very plausible explanation is the placebo effect. We know that belief in a treatment’s efficacy can and does produce powerful benefits.

There’s also the fact that we are not very good at observing ourselves objectively. I am reminded of Sigmund Freud’s paper Über Coca in which the father of psychology details the results of his experiments with cocaine. He finds increased self-control, that he is more vigorous and capable of work, but overall that he is simply normal and as though hardly on a drug at all. Some of the letters he wrote at the time, contrarily, indicate that he was high as balls.

While Ms Peterson needs to be challenged, so too does her father, an acclaimed social scientist, who might not be an expert on the medical literature of nutrition, but who surely has the wherewithal to examine it before promulgating his daughter’s quackery. There is a chasm of difference between “we don’t know everything” and “disregard everything we know”. Prof Peterson says that he’s not recommending the diet, but asks Rogan in his customarily authoritative and irreverent tone, “why is everyone fat and stupid?” He must know that many of his devotees are taking his beef without the requisite pinch of salt.

• Emer O’Toole is associate professor of Irish performance studies at Concordia University, in Canada





