Choosing to avoid meat and eat a plant-based diet has never seemed so virtuous and necessary. Between the intrinsic cruelty of industrial livestock production and livestock’s climate footprint—estimated by the U.N.’s Food and Agriculture Organization to be 14.5% of all greenhouse gases world-wide, significantly greater than that of plant agriculture—it has become increasingly difficult to defend the place of meat and animal-sourced foods in our diets.
Jonathan Safran Foer,
the novelist turned animal-rights activist, may have best captured this thinking in his 2019 nonfiction book, “We Are the Weather: Saving the Planet Begins at Breakfast.” As he writes, “We cannot keep the kind of meals we have known and also keep the planet we have known. We must either let some eating habits go or let the planet go. It is that straightforward, that fraught.”
An essential part of this argument is the proposition that animal-sourced foods, and particularly red and processed meats, aren’t just bad for the planet but harmful for the people who eat them. As the journalist
famously urged in his 2008 bestseller “In Defense of Food,” that is why we should eat “mostly plants.” This has become the lone piece of dietary counseling on which most nutritional authorities seemingly agree. It creates a win-win proposition: By eating mostly (or even exclusively) fruits, vegetables, whole grains and legumes, while getting our proteins and fats from plant-based sources, we maximize our likelihood of living a long and healthy life while also doing what’s right for the planet.
But is it that simple? A growing body of evidence suggests it isn’t, at least not for many of us.
The other food movement that has won increased acceptance over the past decade is the low-carbohydrate, high-fat ketogenic diet—keto, for short—which has emerged as a direct response to the explosive rise in the incidence of obesity and diabetes. More than 70% of American adults are now obese or overweight, according to the Centers for Disease Control and Prevention; nearly one in 10 is severely obese, and more than one in 10 is diabetic. An unavoidable implication of these numbers is that the conventional wisdom on weight loss—eat less, move your body more—has failed tens of millions of Americans.
These are the people who, sooner or later, may well experiment with alternative approaches, venturing into the realm of fad diets. They may try plant-based eating—vegetarian or even vegan—and if those don’t return them to health, try keto or one of the many variations on low-carbohydrate, high-fat diets, from the original Atkins diet to the South Beach diet to paleo to the latest trend, carnivore. If they find that an unconventional approach works for them, allowing them to achieve and maintain a relatively healthy weight without enduring hunger, that will be their motivation to sustain it. But because this way of eating is most easily accomplished with animal-sourced foods, they may come to believe that what’s good for them (and even their children) isn’t good for the planet.
Keto diets are based on the proposition that, for those predisposed to become obese and/or diabetic, carbohydrate-rich foods trigger that predisposition. That isn’t because of the calories they contain, as the conventional thinking on obesity assumes, but because of the effect these foods have on insulin, the hormone that dominates the regulation of fat storage and fat metabolism. Insulin is secreted mostly in response to carbohydrates—not just in the form of sugars, starches and grains (whole or otherwise) but also fruits and legumes, which are the staples of a well-formulated plant-based diet.
“A high insulin level signals fat synthesis and storage…and a low level, its release as free fatty acid back into the circulation,” observed the Harvard University metabolism and diabetes researcher
George F. Cahill Jr.
in 1971 in the prestigious Banting Memorial Lecture at the annual meeting of the American Diabetes Association. This process is like a switch: When fat cells sense the presence of insulin in the circulation, as Cahill described it, they respond by storing fat and inhibiting its release—and we get fatter. When insulin is undetectable, we burn stored fat for fuel—and we get leaner. The metabolic state of ketosis, from which the keto diet gets its name, happens when carbohydrates are restricted almost entirely and fat provides most of the fuel for the body.
The hormonal, insulin-centric regulation of fat storage and fat metabolism remains textbook medicine. Yet its relevance to obesity has been effectively ignored by nutritionists and obesity researchers, who have overwhelmingly preferred to think that all calories are equally capable of stimulating fat accumulation, that we get fat because we overeat, not because the carbohydrates we consume have some unique ability to stimulate fat accumulation. For some significant proportion of Americans, however, remaining relatively lean and healthy may require minimizing their insulin secretion. This, in turn, means more or less rigid abstinence from carbohydrate-rich foods.
Animal-sourced foods—meat, fish, fowl and even processed meat—typically make up the bulk of this approach to weight control because they are almost entirely protein and fat, with minimal carbohydrates. Until insulin was discovered in 1921 and insulin therapy was put to use treating diabetes, these diets were known as “animal diets.” They were the standard of care for diabetes, delaying death in what today is called Type 1 diabetes, the insulin-dependent form, and controlling the disease indefinitely in those with Type 2, the common form associated with excess weight and age. This is still the case.
One can certainly be a vegan or vegetarian and still eat a low-carbohydrate, high-fat, ketogenic diet, getting protein and fat from foods such as tofu and tempeh, nuts and seeds, soy and nut butters, and vegetable oils.
groups are dedicated to the practice, and I have interviewed physicians who embrace it. But it is significantly more challenging to pull this off because plant foods, by their nature, are carbohydrate-rich. It is relatively easy to create and sustain a well-formulated ketogenic diet—with all the essential vitamins, minerals and fats—for those willing to eat animal-sourced foods.
When I started reporting on this subject as a journalist 20 years ago, virtually no meaningful research had been published to test the claims of the diet-book doctors—most famously
—who advocated this way of eating. Since then, carbohydrate-restricted diets, keto or otherwise, may have become the most tested diets in history. The website clinicaltrials.gov reports more than 100 clinical trials of ketogenic diets in progress, and nearly 90 completed.
The findings are consistent: Ketogenic eating is safe and effective at controlling both weight and blood sugar. Pick a disease—from Alzheimer’s and anxiety disorders to traumatic brain injury and tumors—and researchers somewhere are probably testing whether eating a ketogenic diet improves its prognosis. In 2019, the American Diabetes Association concluded that low-carbohydrate and very-low-carbohydrate diets (that is, keto) were the only dietary therapies that consistently resulted in beneficial outcomes for adults with diabetes or prediabetes.
In 2017, more than 100 Canadian physicians cosigned a letter to HuffPost declaring that they personally follow keto-like regimens and now counsel their patients to do so too. “What we see in our clinics,” these physicians wrote, is that “blood sugar values go down, blood pressure drops, chronic pain decreases or disappears, lipid profiles improve, inflammatory markers improve, energy increases, weight decreases, sleep is improved, IBS [irritable bowel syndrome] symptoms are lessened, etc. Medication is adjusted downward, or even eliminated, which reduces the side effects for patients and the costs to society. The results we achieve with our patients are impressive and durable.”
The fact that these diets produce such striking results, even if only anecdotally, poses a tremendous challenge to conventional thinking on nutrition. Since the late 1970s, healthy eating has been defined to mean eating mostly plants: fruits, vegetables, whole grains and legumes, with minimal animal fats and red or processed meats. It is the view embodied in the new dietary guidelines issued in December 2020 by the U.S. Department of Agriculture. This diet continues to get endorsed so widely because epidemiologic surveys tell us that this is how lean, healthy and health-conscious people tend to eat.
But these surveys don’t tell us whether these health-conscious people are lean and healthy because they eat this way or because of all the other factors—from socioeconomic privilege to lifestyle—that are associated with health-consciousness. No meaningful experimental evidence—no clinical trials—exists to support the contention that we would live longer, healthier lives by eating mostly plants rather than animal-sourced foods.
In the early 2000s, when I interviewed several hundred clinicians, researchers and public-health authorities for my first book on nutrition science, “Good Calories, Bad Calories,” some of the most influential of them readily admitted to using the ketogenic diet themselves. “It’s a great way to lose weight,” the late Stanford University endocrinologist
said to me about the diet. “That’s not the issue.”
Some physician-researchers who used a fat-rich, keto diet to lose excess pounds wouldn’t prescribe it for their patients.
But these physician-researchers wouldn’t prescribe it for their patients, worrying that the risk of causing harm—particularly from the saturated fat in meat and dairy—was too great. That was the issue. They would eat the fat-rich, keto diet themselves until they lost their excess pounds, then they would stop and eat “healthy.” When they regained the weight, they would repeat the cycle.
The big difference between the physicians and researchers who admitted to using keto 20 years ago for temporary weight loss and those eating and prescribing keto today is that the latter now believe these diets are the healthiest way for them and their patients to eat. They don’t worry about the saturated fat their patients will be eating because the clinical trials confirm this way of eating is beneficial, and they can see their patients (and themselves) getting healthier, often over the course of weeks or a few months. They are loath to recommend anything else.
I have interviewed more than 120 of these physicians, who tell me that they chose medicine as a career because they wanted to make their patients healthy, not to manage chronic disease. Getting their patients off carb-rich foods—at the very least, sugars, grains and starches—and eating something akin to keto makes that happen. When public-health authorities argue that a healthy diet for all means “mostly plants,” they make the job of these physicians and the challenge to their patients that much harder.
Though arguments for low-carb, high-fat diets have made inroads with medical and public-health authorities, many continue to have reservations. “I have prescribed very low-carb eating strategies for many patients because they could not achieve results with more traditional eating plans,” says
Dr. Michael Dansinger,
an expert on dietary and weight-loss measures at Tufts University’s School of Medicine. But he says that the same is true for very low-fat vegetarian eating plans. He remains concerned about the potential cardiovascular dangers of saturated animal fats. “For the environment,” he says, at the very least, “there is no question that eating less beef can make a favorable impact.”
The Harvard nutritional epidemiologist
Dr. Walter Willett,
probably the most influential academic researcher arguing for plant-based eating, agrees that reducing insulin secretion in those with obesity and diabetes is vitally important, but he doesn’t see the ketogenic extreme as necessary for most. People can accrue “major physiological benefits,” he says, by improving the quality of the carbohydrates they consume—eating whole foods instead of highly processed grains and sugar—without having to avoid carbohydrate-rich foods entirely. “If someone wants to go on a ketogenic diet,” Dr. Willett says, “it could easily be plant-based and even vegan. While we don’t have a study that specifically addresses this, a predominantly plant-based ketogenic diet would be much better for planetary health, and very likely for human health, than a high meat and dairy ketogenic diet.”
Would the millions who might benefit from keto embrace such a diet? Perhaps, but as with any eating pattern, the degree to which people enjoy the recommended foods has a strong bearing on whether they will stick to them. For many people, meat and meat-based foods provide satisfactions that plants cannot. So the tension remains: The healthiest diet for those predisposed to become fat and diabetic may not be what’s healthiest for the planet.
Laboratory-grown meat and fish products may help to resolve this conflict in the future, though reasons for skepticism include both health and gustatory concerns. And we can certainly raise livestock in ways that are better for the environment and make the practice more sustainable. The Food and Agriculture Organization estimates that better feed and feeding practices, better grazing management and animal husbandry can reduce greenhouse-gas emissions by a third in many areas of the world.
But no one can tell us whether we should subordinate our own health and well-being—and perhaps that of our children too—to that of the planet. That is a personal decision. If that trade-off is the reality of our food situation in the century ahead, we have to accept the consequences when we make our choices.
—Mr. Taubes is the author, most recently, of “The Case for Keto: Rethinking Weight Control and the Science and Practice of Low-Carb/High-Fat Eating,” published in December by Knopf.
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