Two weeks ago, a publicist sent me an early copy of a book that claimed it would change everything I thought I knew about food.

That happens a lot. This one caught my eye because it warned of the “hidden dangers lurking in my salad bowl,” and I was eating a salad.

The book, The Plant Paradox, has an image of an artfully smashed tomato on the cover, and it tells readers that eating tomatoes is “inciting a kind of chemical warfare in our bodies, causing inflammatory reactions that can lead to weight gain and serious health conditions.”

Tomatoes and ill-timed references to chemical warfare are, apparently, only a small part of the problem. The Plant Paradox urgently warns against eating wheat, beans, and peanuts, among other plants.

The publisher—the “health, wellness, lifestyle, and inspirational” division of HarperCollins called Harper Wave—elaborates that readers will learn to be wary of compounds found in “grains of all kinds (especially whole wheat), beans and legumes (especially soy), nuts (especially almonds), fruits and vegetables (eggplant, tomatoes, potatoes, peppers, etc.)” in addition to “dairy and eggs.”

That doesn’t leave much on the table. In the midst of soaring rates of obesity and diabetes that many experts believe are clearly linked to an abundance of low-nutrient, low-fiber, sugar-enhanced, heavily processed foods, it could seem an odd time to be warning people against fruits and vegetables. Yet the author, Steven Gundry, appears to be legitimately medically credentialed: a grey-haired, arms-folded, white-coat transplant surgeon whose biography touts a Yale degree. He holds patents on several medical devices, including cardiac cannulae and a suction retractor. He wears glasses. His book carries the endorsement of Dr. Oz.

For readers who are experiencing “cravings, digestive issues, headaches, brain fog, lack of energy, aching joints, morning stiffness, adult acne, or a host of other conditions you just can’t shake,” the publisher’s sell is enticing: “Americans spend billions of dollars on gluten-free diets in an effort to protect their health. But what if we’ve been missing the root of the problem?”

We have been, most health experts agree. But the root of the problem is ... plants?

Come to think of it, I had recently read that Tom Brady and Gisele Bündchen’s diet guru severely limits their tomato intake. (“Tomatoes trickle in every now and then, but just maybe once a month. I’m very cautious about tomatoes. They cause inflammation.”) I thought that might have been an aberrant belief about the pro-inflammatory properties of one plant.

But no. The common factor among foods on the book’s list is a broad category of proteins called lectins. And those proteins are where the author of The Plant Paradox really targets his ire. Gundry writes on his web site, “I believe lectins are the #1 Biggest Danger in the American Diet.”

The book itself is equally severe. It whips readers back and forth between hyperbolic claims of danger and TED-style clichés that confer a sense of superiority upon believers—a promise of being privy to life-altering secrets. The preface begins with a sentence that has almost certainly been written before: “Suppose that in the next few pages I told you that everything you thought you knew about your diet, your health, and your weight is wrong?”

Are you telling me, or is this an exercise in supposition? How do you know what I know? And why do you have access to a truth that no one else in the world has? Is it possible you’re able to presume that your argument will totally upend my understanding of nutrition because the argument is so far afield that no one could take it seriously?

People do, though. In fact, the book seems to be a sort of culmination of a long-percolating hypothesis about the imminent dangers of lectins. It’s especially common among purveyors of dietary supplements. The story goes: We need nutrients to survive, but many plants makes us sick, so synthetic supplement pills and powders are the prudent approach.

The idea is based in just enough evidence to be seriously convincing in the right hands. So for people concerned with “addressing the root of the problem”—unscrupulous marketing messages—and staving off another fad like the global gluten obsession, it’s worth considering lectins.

* * *

In 1988, a British hospital served its staff a special lunch for “healthy eating day.” One dish contained red kidney beans. A medical journal recounts the aftermath. At 3:00 p.m. a surgical assistant vomited in the operating room. Over the next four hours, the hospital staff was rocked by vomiting and diarrhea. I can end the description there.

Everyone recovered by the next day, and tests of the food didn’t reveal any of the common causes of food poisoning. Eventually the incident was traced to the red kidney beans, which have an especially high concentration of the lectin phytohaemagglutinin.

This is a lectin that’s known to be dangerous, and it’s why people read that kidney beans are harmful when eaten raw. For example, a reader of Penn State University’s Home Food Preservation advice site writes: “I read that kidney beans are harmful when eaten raw. Several day care and nursery schools have dry beans (different varieties) out for kids to play with. What danger would there be if a child ate a few of these raw beans?”

Possibly some danger. The site goes on to advise the parent—presumably a parent—that Kidney Bean Poisoning is caused by phytohaemagglutinin, and that different types of lectins are found in many species of beans. As few as four undercooked kidney beans can bring on symptoms, but lectins are inactivated with cooking, “so fully cooked or canned kidney beans are safe to eat.” (Though undercooking may actually increase lectin activity, making the beans more dangerous than were they eaten raw.)

Lectins are a group of proteins that bind to carbohydrates. They are sometimes referred to as a type of “anti-nutrient,” a category that also includes fiber. This term refers to compounds in foods that aren’t nutrients, and whose role in human health is unclear, but may have evolved in plants to dissuade predators.

David Jenkins, a professor of nutritional sciences and medicine at the University of Toronto, explained to me, “Lectins help protect plants from being digested, so they’ve been called anti-nutrients for a long time.” Lectins levels are especially high in legumes (e.g., black beans, soybeans, lima beans, kidney beans, and lentils) and grain products. When eaten in those foods, the lectins typically bind to carbohydrates and pass through the human digestive tract. But when the starches in the above plants haven’t begun to be hydrolyzed by cooking, unbound lectins are free to interact with cells in our intestines. That interaction can, in some cases, cause symptoms of food poisoning.

“Presumably if you take a load of cooked food—with lectins, which may or may not be destroyed by the heat—you’ve also got some floating carbohydrates, so a lot of the lectins are effectively deactivated,” said Jenkins. “But if you eat raw food of certain types––the nightshade family especially and some of the legumes—then you may get a lot of lectins and not much of the carbohydrate that lectins can attack. But they can attack the carbohydrate on your cells. So maybe it’s not a good idea.”

Stories of lectin poisoning are not especially rare. In The Independent the food writer Vicky Jones describes a dinner party in which she used Greek butter beans in a dish without boiling them first. Soon everyone was violently ill. It came on so quickly that before they could consider going to the emergency room, “death seemed preferable to [trekking to the] hospital.”

Jones recovered fully, as most lectin-poisoned people do. Most. There are cases like that of the most famous person to be killed by an umbrella, the dissident journalist Georgi Markov. This was in 1978. He was standing at a bus top when something pierced the back of his thigh. It was an injection delivered through the tip of an umbrella carried by a man who ran off.

Markov grew febrile and died four days later. Pathology reports said the cause of death was a microscopic dose of the poison ricin. Ricin is found in the seeds of the castorbean plant, a shrub-like entity with large, long-stemmed leaves. In a world that fetishizes natural products and remedies, ricin is as natural as natural gets. And it is, you guessed it, a type of lectin.

Which then makes you think, maybe the bookseller’s reference to lectins inciting chemical warfare in our bodies isn’t far off?

* * *

The author Steven Gundry left his position as chairman of cardiothoracic surgery at Loma Linda Medical Center 15 years ago to focus on food-based health interventions. The departure was occasioned by a personal bodily transformation that included shedding 70 pounds. According to his bio at the World Wellness Institute, he and his wife, Penny, now live in Palm Springs and Montecito, California, with their three dogs, Bella, Black Pearl, and Fanny Foo Foo.

Gundry graduated from Yale in 1972 and went on to earn a medical degree from the Medical College of Georgia, though the latter affiliation is rarely mentioned when he gives interviews and does promotional videos about his “revolutionary new method.” Today he is, he says, in high demand from patients around the world. His list of patients includes the self-help entrepreneur and seller of dietary supplements Tony Robbins. I asked Gundry how that came about.

“Tony called me up one day, says, ‘Hey, can I come and see you?’” he told me recently. “I go, ‘Oh, hi, Tony.’ He says, ‘I think I want you to be my doctor.’ And I say, ‘Okay.’ And I still remember the day.”

The story wasn’t as good as I had hoped. But it ended with a captivating moment: “We sat in the exam room and we chatted, and he left and he said, ‘You know I’m a really good judge of character. I’m a judge of the real deal. And he says, you know something, you’re the real deal. And yeah, I want you to be my doctor.”

The decision wasn’t clearly lectin-related. I asked Gundry when he became convinced that these were the leading danger in our food system. “I first studied the effect of plants on humans for my Yale thesis,” he said, “… and it was a 185-page thesis, and luckily I got honors on it.” From there he told of his personal transformation, when he was “so overweight despite running 30 miles a week and going to the gym one hour every day.”

That’s an impressive amount of time in the gym for anyone, much less a surgeon. I didn’t get a clear picture of the origin of his lectin conviction, but he did assure me that he is reaching people.

“The interesting thing about my whole program is that I have never advertised what I do,” he said, describing a long wait list at his practice. I pointed out that I had watched a YouTube infomercial that lasted almost an hour.  I asked, “In what sense do you not advertise?”

“Oh, I mean, my practice. I’ve never gone and spoken to an audience, you know, come and be my patient. I’ve never taken an ad in a newspaper, come and be my patient. And the YouTube is not to get patients into my office, it’s to have them try supplements.”

Yes, he also sells supplements he recommends. The last 20 or so minutes of his infomercial is a string of claims about how supplies are running low, and it’s important that you act immediately, and that if you do manage to get through to a customer representative you should order as much as you have room to store—the shelf life is great, etc. And the necessity of supplements is the crucial argument of the book. He writes, “Getting all of the nutrients you need simply cannot be done without supplements.”

The GundryMD line of products includes something he invented called vitamin G6. Another is a “lectin shield” that’s “designed to neutralize the effects of lectins.” These are available on his website for $79.99. There you can also get six jars of Vital Reds for $254.70. (Despite the name and claims to “boost energy and metabolism,” these reds claim not to be amphetamines.) I asked him when he got into the chemistry business.

“For years and years and years and years, my patients would complain to me, ‘Why don't you come out with a line of powders?’” he said. “Because I hate swallowing pills, and I hate going to four different, five different stores and getting the supplements you want me to take. Why don't you just come up with your own line?’ And I’d go, yeah, yeah, yeah. And my first three supplements were powders, because I listened to my women patients say, ‘Please, don't make us swallow pills. They hate it.”

Gundry assured me that the conflict of interest shouldn’t undermine his authority. “Unlike a lot of other books I've seen which are basically hawking products, this book is hawking getting yourself healthy with basically correct food choices.”

“Right—”

“Now, if they want to buy my products, that’s fine. You know, I’ll certainly tell people what they are.”

* * *

This degree of conflicts of interest is, in science and journalism, the sort of thing that invalidates an expert opinion. But the books and YouTube videos succeed because they strike at a primal type of fear. It’s easy to reason that if there’s even a 1-percent chance that this doctor is right, why not play it safe and avoid lectins?

For one, some research suggests that certain lectins could actually be beneficial in activating elements of the immune system. A lectin in mistletoe, for example, seems to inhibit growth of tumor cells. The evidence is very preliminary, but it’s enough to suggest that these proteins aren’t simply tolerable in small amounts, but that exposure to them serves a purpose.

The much stronger evidence is that the longest-lived, healthiest people in the world tend to subsist largely on plant-based diets. (Those include lectins, often in abundance.) This case for basing a healthy life around what seems to be working for large groups of people in the real world is famously argued by Dan Buettner in his explorations of what he calls “the blue zones,” the homes of the world’s longest-lived people. This suggests that some degree of exposure to lectins could be beneficial, in the same way that sunlight and water are both toxic and necessary to human health, depending entirely on dose and context.

I asked Gundry about those long-lived people. “Grains and beans are negative aspects of the Mediterranean Diet that are countered by the large amounts of olive-oil polyphenols, large amounts of red-wine polyphenols, and fish,” he said. “Dan, I think, has missed the point of the blue zones. The commonality is that all of the blue zones eat a very limited animal-protein diet.”

David Jenkins remains unconvinced. By phone from Toronto, he reminded me that in most places, past generations ate more seeds and beans and nuts than many people do today. “Now even if you go to Boston, the home of Boston Baked Beans, you’ll rarely see a baked bean,” he said. “In Europe, the Dutch used to eat 30 grams of beans a day at the turn of the 19th century. They don’t eat a bean now,” he continued, rattling off several other examples of the recent decline of beans.

“So what I’m saying is that if [Gundry] is right, we should be getting much better, because we’re cutting these things out of the diet. We’re eating a diet of, basically, processed wheat, which is white flour with very little lectin. And we’re eating more meat. Our current dietary habits are steering away from plant foods, and that doesn’t seem to have made us healthier.”

Jenkins speaks with a clinical British lilt, in bursts broken by word-choosing pauses. He notes that just because a substance seems to disrupt digestion in some context doesn’t mean it’s evil in every context. The “anti-nutrient” fiber was, for example, once thought to be worthless since it wasn’t digestible. Now it appears to be extremely beneficial.

“I think you’re on stronger epidemiological ground if you say that processed food is associated with ill health in Western cultures, rather than plant foods. There's some validity to the idea, but I think he may be aiming his guns in the wrong direction,” said Jenkins.

This would counter Gundry’s claim that “lectins don’t get broken down by your GI tract, so they disrupt your digestion [and] reduce energy absorption.”

“If you look around, if you go to any of the beaches in North America—and certainly the lakes—you’ll see the size of people increasing,” said Jenkins. “I’ve watched it over the last 30 years.  

“I think one's got to be careful, because this may be much more importantly nuanced.”

Nuance, though, is an enemy of marketing. I also asked Gundry why the dangers of lectins didn’t appear in his first book, Dr. Gundry’s Diet Evolution: Turn Off the Genes That Are Killing You and Your Waistline (Amazon lists it as a “number-one bestseller in genetics”). He blamed his editor for the omission. He was working with another publisher at the time, and though he wanted to include lectins on his list of things to avoid, he claims the editor said, “I don't care if you can prove it, I need to sell books. And you’re gonna help me.” So the faithful author acquiesced and permitted soy and grains.

“It became a very good selling book, so all is well,” Gundry said. “But when people would come to my office, I would give them the original list.”

A great challenge for the capitalist approach to health is how to sell products without misinforming or misleading people. If the goal of advertising is to make a lot of people want to buy your product––or feel that they need it––there is plenty of grey area in which to manipulate scientific claims.

Book publishing remains one of the industries that drives health trends, with “M.D.” being valuable currency on covers. It tells readers that this is the work of an expert to be used as a reference for your health. For some publishers, conflicts of interest like Gundry’s don’t seem to preclude an author from being sold as the definitive expert on the pathology whose existence necessitates purchase of products sold by the author.

I asked Harper Wave (the imprint of HarperCollins) for a comment on the decision to publish and sell Gundry’s book in this way. I got no reply. Though, at some point since then and my interviews a week ago, the supplement infomercial I mentioned above has been deleted from YouTube.

Book publishers are rarely held accountable for publishing invalid health information. Rather, there seems to be an incentive to publish the most outlandish claims that purport to upend everything the reader has ever heard. This is a problem much bigger than any plant protein. Cycles of fad dieting and insidious misinformation undermine both public health and understanding of how science works, giving way to a sense of chaos. It seems that every doctor has their own opinion about how to protect your body from calamity, and all are equally valid, because nothing is ever truly known.