Diet Cults
This will be shorter than my usual book reviews and is something of an afterthought. I just finished writing a long article on “Food Myths” that Michael Shermer had asked me to write as a cover article for an upcoming issue of Skeptic magazine, and while researching the subject I read a book that someone had suggested to me (I’ve forgotten who you are, but thank you!). It occurred to me that since not everyone who reads SBM subscribes to Skeptic, it would be good to tell this audience about the book too.

(Note: if you subscribed, you could not only read my upcoming “Food Myths” article but also my regular SkepDoc column and my long article “On Miracles” in the next issue. And there’s lots of other great stuff in the magazine, including the Junior Skeptic section for your kids and grandkids. A digital subscription is available for only $14.99 and you can even get a trial issue for free, so you have no excuse not to check it out. End of commercial.)

The book is Diet Cults: The Surprising Fallacy at the Core of Nutrition Fads and a Guide to Healthy Eating for the Rest of Us, by Matt Fitzgerald, an endurance sport and nutrition writer. Not a doctor, but he understands science better than a lot of doctors who have written about diet and nutrition. His reasoning is persuasive and is supported by the scientific evidence.

One of his theses is that humans have a natural propensity to make moral judgments about others’ food choices. This probably developed because it was a practical way to encode trial and error knowledge about safe and unsafe foods, then it became hardwired into human behavior because of the survival advantage for group cohesion. Taboo foods and religious dietary laws like kosher and halal define “our tribe” and emphasize our difference from “others.” We can see a similar group solidarity, peer pressure, moral stance, and semi-religious zeal among today’s environmentalists and animal rights activists.

He argues that most people initially choose diets because of emotional and social factors, and then cherry pick the published evidence (if there is any!), using confirmation bias and rationalization to find post hoc reasons for their unreasoned choices.

Fitzgerald handily debunks the arguments for the Paleo Diet. There was no one paleolithic diet: our Stone Age ancestors ate a variety of diets determined by whatever they could get. Anyway, we couldn’t possibly eat like they did because their food sources are long gone. Today’s plants and animals have been drastically altered by selective breeding. The corn we eat is a far cry from the “natural” teosinte gathered by early humans. Arguments that we should eat what we evolved to eat are undercut by three facts: humans have continued to evolve since the Paleolithic (adult lactose tolerance is one of many examples), and humans evolved to be adaptable and to thrive on a wide variety of dietary intakes; and we evolved to have the survival advantage of intelligence and inventiveness to develop technology to improve our access to food (for instance, cooking). In other words, technology is “natural” for humans, and eating in a variety of ways is natural for humans too. If our ancestors had been less adaptable and if there was a single healthy diet, humans could not have spread to new continents or survived the climate changes of the Ice Age.

He says:

Science has not identified the healthiest way to eat. In fact, it has come as close as possible (because you can’t prove a negative) to confirming that there is no such thing as the healthiest diet. To the contrary, science has established quite definitively that humans are able to thrive equally well on a variety of diets. Adaptability is the hallmark of man as eater. For us, many diets are good while none is perfect.

I think he’s right. If science had identified one optimum diet for human health, all the fads and arguments could have stopped by now. Despite the uncertainty, the existing scientific evidence does seem to be converging towards certain principles that most experts can agree on. There is good evidence that a diet high in fruits and vegetables is healthier than the typical American diet high in calories, red meat, and processed foods.

Fitzgerald provides a 10-item hierarchy of foods from more healthy to less healthy:

  • Vegetables
  • Fruits
  • Nuts, seeds and healthy oils
  • High quality meat and seafood
  • Whole grains
  • Dairy
  • Refined grains
  • Low quality meat and seafood
  • Sweets
  • Fried foods

He recommends that we eat more of the categories higher on the list, and less as we go down the list. No foods need be prohibited.

One could certainly argue with his list, and it hasn’t been tested to see if his plan will actually keep people healthier or make them live longer, but it seems to me that it is at least as reasonable as anyone else’s diet advice. Why not follow this plan while we are waiting for more conclusive scientific evidence? It is flexible, accommodates individual preferences, avoids extremes, and is consistent with the best evidence that we do have.

We don’t just eat for health, we also eat for enjoyment. Why deny ourselves some of the greatest pleasures of life on the basis of diet fads and recommendations that are based on uncertain evidence?

Fitzgerald covers a wide variety of topics such as superfoods, low-carb, protein supplements for weightlifters, sugar, grains, dairy foods, vegetarian diets, dehydration, weight loss, severe calorie restriction for longevity, and many more. The book is well-written, accessible, and a treasure trove of scientific study results and interesting trivia about diet. I enjoyed it, and I think you would too.

Posted by Harriet Hall

Harriet Hall, MD also known as The SkepDoc, is a retired family physician who writes about pseudoscience and questionable medical practices. She received her BA and MD from the University of Washington, did her internship in the Air Force (the second female ever to do so),  and was the first female graduate of the Air Force family practice residency at Eglin Air Force Base. During a long career as an Air Force physician, she held various positions from flight surgeon to DBMS (Director of Base Medical Services) and did everything from delivering babies to taking the controls of a B-52. She retired with the rank of Colonel.  In 2008 she published her memoirs, Women Aren't Supposed to Fly.