top of page
  • Writer's pictureIslon Woolf MD

Cognitive dissonance from conflicting dietary claims

Updated: May 2, 2020

In cognitive dissonance theory, first proposed by Leon Festinger in the 1950’s, the human brain does not like to hold two or more conflicting beliefs and does its best to try to resolve the conflict. Here, I will discuss an example of cognitive dissonance generated when the claims of a new diet conflict with an older diet. I will discuss how people typically resolve cognitive dissonance and how cognitive dissonance can be an opportunity to open the mind to critical thinking. ​

The Old Diet - Vegan

My sister-in-law attends regular lectures at The Hippocrates Institute in Palm Beach. They promote curing of disease with a vegan diet despite well publicized disastrous outcomes. Such as Steve Jobs, who disobeyed his doctors recommendations initially and decided to

Brian Clement Islon Woolf

treat his pancreatic cancer with a vegan diet. The Hippocrates institute is run by a Brian Clement (pictured right) who calls himself "doctor" despite the absence of credentials, and has been the subject of investigation by the Florida Board of Medicine.

He has been accused of causing the death of cancer patients (including children) by giving advise to forgo chemotherapy in lieu of a vegan diet and detox program. (For certain cancers like childhood leukemia, chemotherapy is lifesaving and curative. This is not to be confused with palliative chemotherapy that is given to patients with metastatic solid tumors and typically only gives a few additional months. Those kinds of details, however, are probably lost on someone that has not formally studied medicine). Despite all of these warnings my sister-in-law still finds the Hippocrates Institute a reliable source of information and tries to adhere by most of their recommendations.

Plants = good.

The New Diet - plants are not our friends

Tony Robbins new diet islon woolf

Recently, my sister-in-law attended a Tony Robbins seminar (pictured left accompanied by well researched claim) in Boca Raton where he was promoting a new diet book, The Plant Paradox. The author, Dr Steven Gundry, is a heart surgeon that has shifted his interests from surgery to wellness and lifestyle, and has a penchant for supplements. (Walking in the footsteps of Dr Oz?). Gundry presents an argument that a class of proteins found in plants known as lectins are the 'one true cause of all disease'. It turns out that plants are not our friends, and in fact, they have been waging chemical warfare with us ever since animals started eating them. Gluten, believe it or not, contains a lectin (gliadin), and you know how horrible gluten is. But gluten is just the tip of the iceberg. In fact, all beans, all grains, seeds, nuts, soy, dairy, eggs, and many other fruits and vegetable have high levels of lectins. So forget gluten - lectins are the new gluten.

Lectin are the new gluten

He also claims that we should avoid any plant from the New World (corn, potatoes, tomatoes, avocado, goji berry, chia seeds, etc) because we did not evolve around them.

Steven gundry concierge medicine

Instead of boring you with the details of his evidence, I will review the type and quality of evidence. The Plant Paradox cherry-picks observational studies of nutrition - aka epidemiologic evidence. This is a strategy common to almost every hypothesis in nutrition. Find a population that eats a certain food and attribute all their health or lack of health to that food. Authors will throw around the Inuit, or Pima Indians, or rural Chinese, or Blue Zones, or Tibetan Sherpa guides, or the Maasai, or the French, or the Italians, or Bulgarian farmers, or American mid-westerners, or Belgians during wartime. Whichever observations supports your hypothesis. However, most authors neglect to mention the counter-examples of populations that don’t fit their hypothesis, and how flawed and confounded observational studies are in the first place. Gundry often references the "Paleo Diet” of people living in the Paleolithic. This brings an even higher level of inaccuracy because we do not know their diet, health status, or longevity. It is a misunderstanding of evolutionary biology. There was no one single environment that humans evolved and evolution does not shape for health and longevity - but reproduction. (TED talk debunking Paleo Diet).

Find a population that eats a certain food and attribute all their health or lack of health to that food.

Next comes the smattering of carefully selected impressive sounding biochemical pathways and animal studies, followed by references to poorly understood hot fields in biology such as epigenetics, gut microbiome, leaky gut, and aging. And finally, as expected, the book is chock-full of personal anecdotes (Gundry himself was able to lose weight on his own diet), testimonials, and miraculous cures of every sort. Lupus, arthritis, autism - you know the list. It’s like somebody made a single template 60 years ago on 'how to write a diet book' and every publisher insists on using it. However, some of the statements he makes are just out there, like “Humans were 10 feet tall 10,000 years ago and our brains were 15% bigger”. This concerned me - if he can make wildly speculative statements like this, what does that tell you about the credibility of the rest of his statements. Is he a credible source of information?

If he can make wildly speculative statements like this, what does that tell you about the credibility of the rest of his statements.

Gundry’s purpose in writing the book was to confirm his hypothesis (and also to sell supplements). However, a heart surgeon should know that in science it is more important to try to disconfirm your hypothesis. This is best accomplished by peer review. Submit your idea to a journal and the editors will tear it apart. It’s like a big reality check. However, I can’t find a single article published by Steven Gundry in the entire library of medicine. Nor can I find other articles by other scientists that go beyond speculation proving the role of dietary lectins in disease. Nor can I find any clinical trials. Search for yourself.

But why would Gundry submit his ideas to peers that are equipped with tools to dismantle those ideas? Who wants to have their beliefs challenged? Why not by-pass peer review, and instead, all he has to do is convince Tony Robbins and my sister-in-law. Don’t get me wrong, both Tony Robbins and my sister-in-law are very smart - but not in medicine, evolutionary biology, botany, immunology, biochemistry, and statistics. Gundry can talk circles around them - and he does.

Why not by-pass peer review, and instead, all he has to do is convince Tony Robbins and my sister-in-law.

Cognitive Dissonance ensues

I obviously do not find the evidence strong nor the sources credible for either of the above nutritional claims - Vegan or Plant Paradox. However, my sister-in-law does. In fact, she finds both claims and the source of the claims highly credibl. So much so, it has generated tremendous cognitive dissonance in her brain. One reliable source of health information, Tony Robbins, is claiming something completely different from another reliable source, the Hippocrates Institute. Currently, she believes that if something is natural it must be good for you. (This is a common logical fallacy known as the appeal to nature). However, now she is being told by a reliable source that plants, the very definition of natural, are not good and not our friends. She desperately needs to figure out how to resolve this cognitive dissonance. Resolution would relax her brain and give her a nice reward - like a shot of dopamine - and she could once again feel good about what she was eating and mildly superior to everyone else.

Ways to resolve the Dissonance

Most people try to resolve the dissonance quickly. One tactic is to accept the new evidence and simply migrate from one diet to the next, and one trend to the next. Therefore, simply accept the Plant Paradox and change your diet, until the next diet comes along.

The other tactic is to question the validity of evidence of the new claim so you can stick with the old claim - the vegan diet. Unsurprisingly, this is the response of Dr Collin Campbell from the famous China Study and Forks over Knives documentary. Like the Hippocrates Institute, Dr. Campbell along with Dr Esselstyn and Dr Dean Ornish are famous pro-vegan doctors that claim a plant-based diet will cure everything from irreversible heart disease to cancer. Most of their evidence is of the same poor quality as Gundry - cherry-picked epidemiology, animal studies, poorly understood biochemical pathways, and lots of anecdotes. However, in an impressive commentary on the Plant Paradox, Campbell goes into some detail pointing out the weak forms of evidence that Dr. Gundry uses. Frankly, I was surprised that Campbell even knew of the hierarchy of evidence - that some evidence is better than others. This is irony at its best. He who used shitty evidence to confirm his claims is upset by someone else who used shitty evidence to confirm opposing claims - and then schools the other guy on shitty evidence. It is like two astrologers coming up with different predictions of the future and one astrologer tells the other that his methods are not rational or scientific.

This is irony at its best. He who used shitty evidence to confirm his claims is upset by someone else who used shitty evidence to confirm opposing claims

It is unlikely that anyone or anything can change Campbell's mind. In fact, cognitive dissonance theory predicts that smart people can believe and hold firmly to stupid things. This is because smart people are better at justifying beliefs they arrived at for non-smart reasons. (A well-publicized example of this is past presidential candidate neurosurgeon Ben Carson. For an excellent lecture of why smart people believe stupid things see Michael Shermer on the topic.)

Smart people are better at justifying beliefs they arrived at for non-smart reasons.

A Pathway To Critical Thinking

Although she finds me less credible than the other mentioned sources, my sister-in-law eventually broke down and asked for my opinion. My advise was different from what she expected. I wanted her to persevere a little more in the dissonance so that she could start to contemplate. I wanted to show her the importance of being wrong. In fact, it has been said you are not a scientist until an idea that you are certain is true is proven to be wrong. It is in the dissonance where critical thinking begins. One starts to generate penetrating questions and deductions:

Judging source credibility :

  1. Two of the sources I find credible have conflicting ideas. Therefore, at least one has to be wrong.

  2. If this is true, maybe I am not as good as I thought in judging the credibility of a source.

  3. What criteria do I use to determine if a source is credible?

  4. Maybe I equated the confidence of the speaker with the truth of the information?

  5. Maybe other inherent biases drove me to agree with the source?

  6. Does the source actively seek out disconfirmation from his peers?

Interpretation of evidence:

  1. If both sources have access to the same evidence why are they coming up with different answers?

  2. What kind of evidence did they use to support their claims?

  3. Are some kinds of evidence more reliable than others?

  4. What kind of evidence would definitively prove one food group is better than another

  5. Is the answer to the question, “What do we eat?”, knowable at this point?

Self reflection:

  1. Am I equipped to evaluate these complex ideas?


I have been evaluating nutritional claims for the past 30 years. One can't help notice the dramatic vacillation of nutritional advice. "Eggs are good for you", "no, eggs are bad for you", "no, eggs are good for you". There are many explanations for these strong conflicting opinions. I believe it can be explained by the weak forms of evidence which support these claims. Evidence that can be easily twisted and cherry-picked to support just about any hypothesis.

Stronger forms of evidence, like randomized clinical trials, would be helpful to resolve these conflicts. However, nutritional clinical trials are expensive, require years of follow up, and are difficult to maintain subject compliance.

Despite this obvious evidence gap, nutritional claims continue to be streamed to the public with extreme confidence from respected authority figures. It’s no wonder my sister-in-law is experiencing cognitive dissonance.

At present I am my brain is perfectly resonant with the following conclusion - we don’t yet know. Other than, avoiding Doritos, Coca Cola, and bacon, its hard to say what people should eat. I wonder if my sister-in-law will ever get there? I will keep you informed.


bottom of page