Keys was born in 1904 into a moderately distinguished family in California (his uncle was the movie star Lon Chaney, to whom he bore a striking resemblance). He was a bright but undermotivated child. Professor Lewis Terman of Stanford, who studied intelligence in youngsters (he was responsible for putting “Stanford” in the Stanford-Binet IQ test), declared the young Keys a potential genius, but Keys chose not to fulfill his potential. Instead, he dropped out of school at fifteen and worked at a variety of exotic jobs, from sailor in the merchant navy to a shoveler of bat guano in Arizona. Only then did he belatedly embark on an academic career, but he made up for lost time in a big way, rapidly acquiring degrees in biology and economics from the University of California at Berkeley, a PhD in oceanography from the Scripps Institution in La Jolla, California, and a second PhD, in physiology, from Cambridge University in England. After settling briefly at Harvard, where he became a world authority on high altitude physiology, he was lured to the University of Minnesota to become the founding director of its Laboratory of Physiological Hygiene. There he rapidly became an expert on human nutrition. When America joined the Second World War, the War Department commissioned Keys to devise a lightweight food pack for paratroopers. The result was the imperishable army food known as K rations. The K stood for Keys.
In 1944, as much of Europe faced the prospect of starvation because of the disruptions and privations of war, Keys embarked on what became known as the Minnesota Starvation Experiment. He recruited thirty-six healthy male volunteers—all conscientious objectors—and for six months allowed them just two meager meals a day (one on Sundays) for a total daily intake of about 1,500 calories. Over the six months, the men’s average weight dropped from 152 pounds to 115. The idea of the experiment was to establish how well people could cope with the experience of chronic hunger and how well they would recover afterward. Essentially, it just confirmed what anyone could have guessed at the outset—that chronic hunger made the volunteers irritable, lethargic, and depressed, and left them more susceptible to illness. On the plus side, when their normal diet was resumed, they quickly recovered their lost weight and missing vitality. On the basis of the study, Keys produced a two-volume work, The Biology of Human Starvation, which was highly regarded, though not particularly timely. By the time it came out, in 1950, nearly everyone in Europe was well fed again and starvation was not an issue.
Soon afterward, Keys embarked on the study that would permanently seal his fame. The Seven Countries Study compared the dietary habits and health outcomes of 12,000 men in seven nations: Italy, Greece, the Netherlands, Yugoslavia, Finland, Japan, and the United States. Keys found a direct correlation between levels of dietary fat and heart disease—a conclusion that is hardly surprising now but was revolutionary then. In 1957, with his wife, Margaret, Keys produced a popular book called Eat Well and Stay Well, which promoted what we now know as the Mediterranean diet. The book infuriated the dairy and meat industries, but it made Keys rich and universally famous, and it marked a milestone in the history of dietary science. Before Keys, nutritional studies had been directed almost entirely at combating deficiency diseases. Now, people realized that too much nutrition could be as dangerous as too little.
Keys’s findings have come in for some sharp criticism over the years. One commonly heard complaint is that Keys focused on countries that supported his thesis and ignored those that did not. The French, for example, eat more cheese and drink more wine than almost anybody else on Earth and yet have some of the lowest rates of heart disease. This “French paradox,” as it is known, led Keys to exclude France from the study because it didn’t fit with his findings, critics have claimed. “When Keys didn’t like data,” says Lieberman, “he just eliminated them. By today’s standards he would have been accused and fired for scientific misconduct.”
Keys’s defenders have argued, however, that the French dietary anomaly wasn’t widely noted outside France until 1981, so Keys wouldn’t have known to include it. Whatever else anyone concludes, Keys surely deserves credit for drawing attention to the role of diet in maintaining heart health. And it must be said it did him no harm. Keys devoted himself to a Mediterranean-style diet long before anyone had heard of the term and lived to be a hundred. (He died in 2004.)
Keys’s findings have had a lasting effect on dietary recommendations. The official guidance in most countries is that fats should account for no more than 30 percent of a person’s daily diet, and saturated fats no more than 10 percent. The American Heart Association puts it even lower at 7 percent.
Now, however, we are not quite so sure how solid that advice is. In 2010, two large studies (in The American Journal of Clinical Nutrition and the Annals of Internal Medicine) involving almost a million people in eighteen countries concluded that there was no clear evidence that avoiding saturated fat reduced the risk of heart disease. A similar and more recent study in the British medical journal The Lancet in 2017 found that fat was “not associated with cardiovascular diseases, myocardial infarction, or cardiovascular disease mortality” and that dietary guidelines consequently needed to be readdressed. Both conclusions have been heatedly disputed by some academics.
The problem with all dietary studies is that people eat foods that have oils, fats, good and bad cholesterol, sugars, salts, and chemicals of every description all mixed together in ways that make it impossible to attribute any particular outcome to any one input, and that is not to mention all the other factors that affect health: exercise, drinking habits, where you carry fat on your body, genetics, and much more. According to another, oft-quoted study, a forty-year-old man who eats a hamburger every day will knock a year off his life expectancy. The trouble is that people who eat a lot of hamburgers also tend to do things like smoke, drink, and fail to get adequate exercise that are just as likely to cause an early checkout. Eating a lot of hamburgers is not good for you, but it doesn’t come with a timeline.
These days the most frequently cited culprit for dietary concern is sugar. It has been linked to a lot of horrible diseases, notably diabetes, and there is no question that most of us take in way more sugar than we need. The average American consumes twenty-two teaspoons of added sugar a day. For young American men, it’s closer to forty. The World Health Organization recommends a maximum of five.
It doesn’t take much to go over the limit. A single standard-sized can of soda pop contains about 50 percent more sugar than the daily recommended maximum for an adult. One-fifth of all young people in America consume five hundred calories or more a day from soft drinks, which is all the more arresting when you realize that sugar isn’t actually very high in calories—just sixteen per teaspoon. You have to take in a lot of sugar to get a lot of calories. The problem is that we do take in a lot, more or less all the time, often when we don’t even know it. For one thing, nearly all processed foods include added sugar.
By one estimate, about half the sugar we consume is lurking in foods where we are not even aware of it—in breads, salad dressings, spaghetti sauces, ketchup, and other processed foods that don’t normally strike us as sugary. Altogether about 80 percent of the processed foods we eat contain added sugars. Heinz ketchup is almost one-quarter sugar. It has more sugar per unit of volume than Coca-Cola.