In the early 1970s, psychologists at Northwestern University conducted an experiment that, on the surface, looks like a child’s imagination. Researchers gathered 45 college women and asked them to drink a shake or two. Then they placed three pints of ice cream in front of each woman and asked her to eat each one. Afterwards, they told each participant to “help herself to the rest of the ice cream, as she wanted,” the researchers wrote in the paper. Journal of Personality. Finally—and this was key—each woman completed a survey measuring how much food she ate or “restricted,” outside of the medications she took.
The findings were dramatic. On average, women who said they were not dieting or worried about weight ate less ice cream if they drank at least one shake. The first sweet meal satisfied their hunger. But for women who are dieting and concerned about their weight, the milkshake seems to bring out hidden hunger. On average, they ate 66 percent more ice cream after the milkshake than they did without it.
From this data, the researchers developed a bold new theory: Diet and weight anxiety cause people to overeat and gain weight. Dieting remains very pervasive in American culture, but the Shake Shack study, and similar research that followed, however, changed many Americans’ views on diet and obesity. Experts have concluded that all kinds of eating disorders—including anorexia, binge eating, and bulimia—can be brought on by deliberately reducing the number of calories you eat. Some scientists believe that food restriction also leads to obesity.
This line of research has inspired treatments for eating disorders, helped launch the anti-diet movement, fueled the so-called junk food trend, and changed how parents encourage their children to think about food. But recent evidence suggests that trying to limit one’s food intake usually doesn’t have such dire consequences.
The idea that trying to diet leads to eating disorders and obesity makes some sense. “There’s this idea that if you find yourself thinking about food, trying to limit what you eat or trying not to eat too much, you’re developing an eating disorder mindset,” Michael Lowe, a psychologist at Drexel University, told me. The idea is also naturally appealing, in that most people don’t such as Avoiding spicy foods; They can easily believe that doing so will be harmful. Not surprisingly, then, this idea has spread among clinicians and everyday Americans. Social media has fueled this theory, so many people now believe it which University of Michigan psychologist Ashley Gerhardt told me that restricting your food intake can be dangerous or harmful. Many parents believe that allowing children to follow their appetites develops healthy eating habits. Taken to its logical extreme, this way of thinking means that “in many circles now, if you don’t allow your kids unlimited access to ultra-processed foods, that’s bad,” Kathryn Balantikin, a registered dietitian at the University of Buffalo, told me.
Such ideas were published even as researchers pointed out major flaws in early studies of the relationship between dietary restrictions and eating disorders. These experiments did not use a fixed definition Diet restrictionand never tested whether it actually causes eating disorders or overeating; They can only say that these behaviors are combined. In addition, many studies combined multiple types of eating disorders, or did not separate participants with obesity from those with low body weight.
Scientists, including those who conducted the 1975 Shake Shack study, also relied on self-reports or surveys to determine how much food participants ate, assuming that people who said they restricted their intake were actually taking in fewer calories. But decades later, when scientists gave the same survey to new participants and measured their calorie intake, they found that the survey simply wasn’t related to calorie restriction, Eric Stace, a psychologist at Stanford who has led some of these measurement studies, told me. Stace found that people who such surveys would label “high dieters” may not have been eating at all. In one of his studies, a so-called high dieter consumed, on average, 23 fewer calories per day than a low dieter. “It’s like not eating four peanuts a day and saying you’re on a diet,” he said.
In the 2000s, scientists began randomized, controlled trials that could more accurately test the model proposed in the 70s. In a series of studies, people were given personalized diets aimed at reducing calorie intake, and taught effective ways to stick to their eating plans. After six months, the volunteers lost about 10 percent of their body weight, on average, compared to the 1 percent that the control group lost. And binge eating did not worsen the participants’ eating disorder symptoms. In fact, it reduced their food intake, and they felt less concerned about their body size (perhaps, in part, because their body size decreased). Over the past decade, psychologists at Yale School of Medicine have conducted similar randomized, controlled studies of people previously diagnosed with binge eating disorder and obesity. And then, on average, calorie restriction reduces overeating; Participants’ eating disorder symptoms worsened only occasionally, and no more than the control group. In at least one article, eating disorder symptoms improved more among people in the restriction group than in the control group. In another, weight loss led to abstinence from cannabis use in nearly three-quarters of participants.
The scientific consensus that has emerged after these and similar studies is far more significant than was suggested 50 years ago—though it still has significant currents in American culture. “Food restriction is not necessarily all good or all bad. But different degrees may be beneficial or harmful for different people,” Sidney Yurko, a psychologist at Yale School of Medicine who participated in the recent trials there, told me in an email. For example, she said, dieting is never recommended for people diagnosed with anorexia nervosa. And even for people without an eating disorder, “the extreme restriction that often accompanies self-directed dieting is largely unhealthy and counterproductive,” Yurko wrote.
A new generation of experiments has also uncovered a surprising way to prevent future eating disorders in high-risk boys and young women: small amounts of effective dietary restriction. A 2021 meta-analysis found that teaching people about healthy eating habits—including how to curb overeating tendencies—prevents the future development of eating disorders. Overall, Stace said, modern experience suggests two possible pathways for the development of eating disorders. The first includes those who are unhappy with their bodies and engage in extreme weight loss behavior to change. “But there’s another way that a lot of people have overlooked,” he said, in which a person eats too much food, gains weight, and then As a result, they become dissatisfied with their bodies.
From this perspective, the Shake Shack study is very different. Fifty years ago, psychologists concluded that dieting caused women to eat more pints of ice cream. But modern interpretation suggests that the opposite was likely true for many of the participants: the underlying tendency to overeat forced women to overeat.
In hindsight, the timing of the Shake Shack study is almost prophetic. In the late 1970s, the food environment in America began to change rapidly, Lowe, the Drexel psychologist, told me. “The availability of fast food, restaurants, and high-sugar, high-fat foods started quickly,” he said. Food became more difficult to resist, even when Americans were not starving. “People have suddenly become very restricted in their diet in order to maintain their weight.” More people began to gain weight, and by the early 80s, the country had entered the first phase of the current obesity epidemic. Today, the average American consumes half of their calories from ultra-processed foods. The exact boundaries of the category cause debate among some scientists, but they generally agree that such foods are highly refined, produced in industrial factories, and high in calories. Studies have found that diets high in these foods can cause people to consume hundreds of extra calories per day, and when people do overeat, they only do so with ultra-processed foods.
Recently, scientists and government leaders have begun warning Americans about the potential harms of eating too much processed food, including an increased risk of diabetes, certain cancers and depression. Health Secretary Robert F. Kennedy Jr. declared war on added sugar, and starting this year, the National Dietary Guidelines advise against eating highly processed foods. In fact, the study of this type of food is just beginning. But if Americans are ever going to understand exactly how such foods affect us, now is the time to abandon the false lessons of the Shake Shake study. Maybe then we explore how we can create a truly healthy relationship with the delicious food around us.
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