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The persistent mystery of protein intake

The persistent mystery of protein intake
The persistent mystery of protein intake

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Scientists still aren’t sure how much we actually need.

Illustration by Matteo Giuseppe Pani. Sources: Getty.

March 14, 2024, 3:57 PM ET

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If nutritional information were a slice of bread, we’d be living in a world full of dense 24-grain-and-seed loaves. The internet is stuffed with listicles, tips, and tricks for consuming the right ratio of “macros” (fats, carbs, and proteins). Rows and rows of vitamins and supplements fill pharmacy aisles. Calorie-counting apps track every savored crumb. But in 1918, the answer to the question “What and how much should we eat?”—the title of an Atlantic article that year—was just beginning to be scientifically understood.

Published in The Atlantic in the waning days of World War I, the story is in part a reaction to living in a resource-strapped country. “Let us first consider the question how much energy is really needed; or, to put it the other way, how little food can we get along on and still do the work necessary for the successful conduct of the war,” wrote Thomas B. Osborne, a revered biochemist. In much of the article, Osborne is consumed, so to speak, with questions of metabolism. Studies and lab experiments had led him to believe that animals—humans included—instinctively knew what types of foods to eat for nutritional value and when to stop eating:

In general, we eat very nearly the amount of food that we really need. He who does hard physical work needs to eat more than does the sedentary brainworker whose labor involves no expenditure of energy that must be supplied by extra food; and so he who works with his brain instinctively eats less than he who works with his muscles.

Osborne’s theories existed in a different food culture, before the days of ultra-processed foods, artificial sweeteners, and the ubiquity of high-fructose corn syrup. With unhealthy foods more accessible than ever, it can be easier for people to overeat or experience nutritional deficits. But food science, a notoriously tricky field, has also evolved substantially. In Osborne’s day, calculating caloric expenditure on the personal level was difficult; now people wear little devices that estimate the number of calories they’ve burned in a day (though questions remain about their accuracy).

But one thing hasn’t changed over these past 100-plus years: We still don’t know the ideal amount of protein to consume. “How much protein should be included in the daily diet, is a question which has been the subject of contention among physiologists and nutrition experts for a long time, and as yet no agreement appears to be in sight,” Osborne wrote. In 2023, the Atlantic science writer Katherine J. Wu reported something similar: “Researchers don’t agree on how much protein is necessary, or how much is excessive; they’ve reached no consensus on the extent of its benefits, or whether eating extra servings can send our health into decline.”

For Osborne, answering the questions surrounding proteins was an obsession. A biography written by his fellow biochemist Hubert Bradford Vickery described Osborne’s “whole-souled devotion to a single purpose, the understanding of the relationships of proteins to each other and to the animal world.” Osborne asserted in 1918 that people eat “more protein than the physiologist tells us is needed for actual maintenance”—and that has mostly stayed true. “American adults consistently eat well above [the recommended] amount, with men close to doubling it,” Wu wrote last year.

There’s much (much, much) discussion over the question of proper protein intake, but the current daily guidelines are set at 0.8 grams per kilogram of body weight. For a 180-pound person, that means consuming roughly 65 grams a day. This value is a stark contrast to what Osborne noted was the average “daily ration” in the early 20th century: “about three and a half ounces of sugar, four and a half ounces of fat, eight and a half ounces of flour, and three and a half ounces”—or roughly 99 grams—“of protein.”

Osborne reasoned that humans know, on the most basic level, what and how much to eat. If we don’t get the kind of protein we need in one kind of food, he posited, we instinctively look to supplement that with a different source. But sometimes, we still wind up eating more protein than we need. “Our instinct assures us of a margin of safety which is doubtless wider than is necessary, but how much wider, no one knows,” he wrote.

His thinking echoes a trend that’s taken hold in recent years: intuitive eating, an approach that relies on paying attention to the body’s signals of hunger and fullness. Its practitioners are taught to consume what satisfies them and denounce diet culture’s calorie counting, an inherent restriction of our eating instincts. Even in food trends, there’s usually nothing new on the dinner plate.

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