Is an All-Meat Diet What Nature Intended?

“Some meatfluencers stress that human beings are animals and maintain that, if allowed to eat according to our animal instincts, we will favor a meaty menu. But the biologists David Raubenheimer and Stephen J. Simpson have been investigating animal alimentation for more than thirty years, and their new book, “Eat Like the Animals,” suggests that the meatfluencers have it all wrong. The authors started collaborating at Oxford, studying the eating preferences of locusts (grasshoppers, basically). First, they found that locusts preferred a certain ratio of carbohydrates to protein. When forced to live on foods higher in carbs and lower in protein, the insects ate a lot, becoming obese, and took longer to molt to adulthood. Conversely, when put on the insect version of the Atkins diet, they ate far fewer calories and were less likely to make it to adulthood. Second, they found that locusts with a decent food selection always ended up with near-identical ratios of protein and carbohydrates. “It’s as if, regardless of whether we were offered meat and pasta, or egg and bread, or beans and rice, or fish and potatoes, we always consumed the exact same balance of protein and carbs.” The critters somehow track which nutrients are in which foods.

These findings aren’t limited to insects. Raubenheimer and Simpson have since determined that the pattern is widespread across the animal kingdom, from beetles to baboons. And they have found that protein-loaded diets don’t just age animals; they kill them faster. “Our sexy, lean mice who ate high-protein, low-carb diets were the shortest lived of all,” they wrote of research published in 2014. “They made great-looking middle-aged corpses.”

Raubenheimer and Simpson find possible lessons here about human metabolism. As ultra-processed foods become stripped of protein, we behave like their protein-deprived locusts, becoming bloated on carbs. The elimination of fibre exacerbates the problem, they write, removing a brake that would otherwise slow eating, fill our stomachs, and curb hunger. At the same time, their work implies a Faustian allure to keto, carnivory, and other protein-heavy regimens. Cutting out carbs may make us skinnier and accelerate tissue development, shifting our bodies into a “growth and reproduction pathway.” But this comes at the expense of longevity. Repair and maintenance systems are sidelined. Misfolded proteins and other cellular junk accumulate. Pushed into overdrive, the body falters.

According to Raubenheimer and Simpson, two canonically healthy populations—the Okinawans, in Japan, who become centenarians at five times the rate of the rest of the developed world, and the Tsimané, of the Bolivian Amazon, who have the lowest incidence of cardiovascular disease ever recorded—consume diets that are, respectively, just nine and fourteen per cent protein. Most of their calories come from fibrous starches, such as plantain, cassava, or sweet potato. Raubenheimer and Simpson don’t propose that readers become Japanese islanders or remote Amazonians, and although they present suggested protein intakes, they warn against following them too strictly. Instead, they advise cutting out ultra-processed foods; finding good sources of fats, proteins, and fibre-loaded carbs; and listening to your appetite (unless you crave savory snack foods, which, they point out, trick the body into thinking that it’s getting protein when it’s not). “Our appetites are better gauges than our calculators,” they conclude. [..]

As a species, humans once ate thousands of plant foods, but only a hundred and fifty are cultivated at scale for food today, three of which—rice, wheat, and maize—constitute fifty per cent of all calories. Even within that trio, diversity is crumbling. In the twentieth century, American-grown hybrid corn came to account for fifty per cent of globally traded maize. Thousands of local varieties have been displaced. The result was a boom in calories but also a more fragile food system, as was made clear when a fungal blight ruined a billion bushels of American maize in 1970. [..]

When, in the nineteen-seventies, Nathan Pritikin championed a high-carbohydrate, low-fat regimen, he and his co-authors claimed that it was “an accident of civilization” that Americans had such easy access to fat and cholesterol. “Primitive people” were “more likely to be near-vegetarians,” he asserted. When Robert Atkins promoted the opposite approach—carbohydrate restriction as the key to good health—he stressed that “the food you eat when you do Atkins is surprisingly close to what our primitive ancestors ate.” And in “Diet for a Small Planet” (1971), perhaps the most important tract in favor of meatless eating ever published, Frances Moore Lappé told her readers that she advocated “the return to the traditional diet on which our bodies evolved.”

Fad diets are perfectly manufactured to spread. They appeal to dissatisfaction. They provide crude explanations for why things are going wrong. And they tap into an intuitive logic at the center of spiritual traditions—that the greater the sacrifice, the greater the redemption. Yet fad diets also doom themselves. The same features that fuel their popularity—their quick-fix nature, their severe and often harmful restrictions—are what make them unsustainable for many.”

Full article, M Singh, The New Yorker, 2023.9.25