Here are a few of the things that can make you hungry: seeing, smelling, reading, or even thinking about food. Hearing music that reminds you of a good meal. Walking by a place where you once ate something good. Even after you’ve just had a hearty lunch, imagining something delicious can make you salivate. Being genuinely hungry, on the other hand—in the sense of physiologically needing food—matters little. It’s enough to walk by a doughnut shop to start wanting a doughnut. Studies show that rats that have eaten a lot are just as eager to eat chocolate cereal as hungry rats are to eat laboratory chow. Humans don’t seem all that different. More often than not, we eat because we want to eat—not because we need to. Recent studies show that our physical level of hunger, in fact, does not correlate strongly with how much hunger we say that we feel or how much food we go on to consume.
That’s something of a departure from commonly held views of what it means to be hungry. Traditionally, hunger has been seen as largely physiological: our body becomes depleted and, to maintain homeostasis—the body’s status quo—certain hormones are released into our bloodstream and stomach to signal to our brain that it’s time to replenish its resources. We eat. We digest. We use up our store of energy. The process repeats. “There are literally thousands of studies on the behavioral and biological effects of prolonged food deprivation,” Michael Lowe, a psychologist at Drexel University who has been researching hunger since the late seventies, told me.
Food deprivation, however, is generally not a problem in modern, developed societies. While our ancestors had to struggle to consume enough calories, we can just go to the fridge or the supermarket. As a result, though newborns behave much like animals and our calorie-deprived ancestors—they eat when they are physiologically hungry (and they let you know when they feel that way)—that internal reliance soon goes away. From an early age, we learn to depend increasingly on external, socially, and culturally based cues. Infants as young as twelve monthsalready show signs of taking eating cues from adults—and the eating behaviors that we learn at home often follow us later in life. Lowe calls it the difference between homeostatic and hedonic eating: eating for need and eating for pleasure.
The idea that environmental cues affect hunger is not a new one. As early as 1905, Ivan Pavlov demonstrated as much by training dogs to salivate when they heard a bell. In the nineteen-seventies, the French obesity researcher France Bellisle proposed that the timing and the size of human meals was “essentially determined by sociocultural factors,” which could, in turn, override the physiological signals sent by our bodies. Physiology, in other words, had become a secondary consideration.
Foremost among those factors is something quite simple: the time of day at which you learn to be hungry. Your scheduled lunch break at work or your usual family dinnertime can reliably set your stomach growling. Even if you’ve had an unusually late or large breakfast, your body is used to its lunch slot and will begin to release certain chemicals, such as insulin in your blood and ghrelin in your stomach, in anticipation of your typical habits, whether or not you’re actually calorie-depleted. New research goes as far as to suggest that when you choose (or don’t choose) to eat may be more predictive of weight loss and gain than the total number of calories that you consume. Our bodies don’t have just a single internal clock that tells us when to sleep and when to wake. Each organ—including the organs related to eating—has a circadian clock of its own, and that clock is sensitive to when, precisely, we eat. If two groups consume the same number of calories but one group eats them during the first part of the day and the other during the second, the latter group is up to two times more likely to be obese. In one study, two groups of people were assigned to eat the same number of calories each day during a twelve-week period. One group received more of them during breakfast, and the other had more during dinner. The breakfast group lost significantly more weight.
In 2011, Mark Bouton, a psychologist at the University of Vermont, conducted a review of the types of conditional and operant stimuli that increase a craving for a specific food or our desire to eat more generally. He found that two types of cues play an important role. On the one hand, there are food-specific cues: a certain packaging or color associated with a preferred food (say, the distinctive red and orange of a Doritos logo and bag), a certain sound (someone opening the bag), a certain smell (the scent of the chips), or a certain taste (a hint of saltiness). But equally important are environmental cues that seem unrelated to food: the couch on which you typically watch movies while eating popcorn, a social gathering like a Super Bowl party, a sporting event, a shopping mall. These cues, in turn, are very difficult to unlearn. If you have a habit of snacking on Oreos while watching “Mad Men,” it will be tough to get through an episode without craving your cookie. (TV, in fact, is a particularly difficult stimulus to control; regardless of other ambient conditions, we tend to eat more when the television is on.)
Even the most weight-conscious, eating-savvy individual may find himself weakening under the constant onslaught of environmental cues telling him to eat, eat, eat. “Our environment is absolutely filled with highly pleasurable foods that are also high in calories, high in fat, relatively cheap,” Lowe said. Each time we give in, we increase the amount of self-control we need not to eat the next time. In an environment in which food is a perpetually available temptation, the costs of constantly resisting are high. There are only so many times that you can let a platter of pigs in blankets pass by before you take one.
Making this worse, if we break down and have a snack—and if it happens to be something that we like—we not only become slightly more hungry in the first minutes of eating but we will grow hungry again sooner. In a series of imaging studies, Lowe and his colleagues observed the brain both when it’s anticipating tasty food and when the food is consumed, and found a disturbing pattern. The first few times people eat a new, pleasurable food, their brain’s reward systems light up—both when they are about to eat and after they’ve done so. Over time, however, something shifts. “If you keep doing this repeatedly, over days, what starts to happen is the strength of the reward response to the actual consumption of the food slowly diminishes, but the reward response to the signal, the cue predicting the food, grows stronger,” Lowe said. In other words, our pleasure centers get excited by the promise of a delicious morsel, but no longer by the consumption. “It’s a vicious cycle,” Lowe said. “The more delicious food you eat, the harder it is to resist. But the actual hit, the reward you get from the food, diminishes, so you want to eat more to get the same reward—but when you do that, you further reduce the value of the food and further strengthen the signal for the food.” Environmental cues get stronger. Physiological responses get weaker. And the cycle of false hunger and very real eating grows harder to break.
Perhaps one of the reasons that weight-loss interventions fail, then, is that they have, for the most part, centered on personal life-style choices: your ability to exercise restraint and self-control. Because environmental temptations only grow stronger over time, individuals who have successfully lost weight may find it increasingly hard to keep it off. It takes more and more effort—in the face of greater and greater environmental resistance. Lowe’s solution is to focus on the environment: the psychological hunger cues that have taken over our basic physiology. “If a lot of the problem that overweight people face is exposure to too much delicious food in growing portions, that has big treatment implications,” he said.
In a study published last month, Lowe asked a hundred and thirty-two overweight individuals to participate in a twelve-week weight-loss program—a traditional approach based on the LEARN(Lifestyle, Exercise, Attitudes, Relationships, Nutrition) model, combining the use of Slim-Fast meal replacements with counselling on lifestyle changes. Participants lost, on average, about thirteen and a half pounds. Lowe then randomly assigned them to one of four maintenance regimes. The first two groups followed one of two approaches that had been taught in the initial program. One group, called the control group, continued to follow the LEARN protocols but, instead of meal replacements, received instructions on how to incorporate conventional food into the diet that would maintain the same caloric intake. For the second group, the meal replacement continued in modified form for one meal and one snack per day.
The remaining two groups were taught a new approach that Lowe refers to as “energy density”: a focus on learning to purchase and prepare foods that, pound for pound, have fewer calories than other foods, based on an approach popularized by the nutrition expert Barbara Rolls in her “Volumetrics” book series. Both groups received regular homework assignments to help them to establish new shopping and cooking habits. They were also taught to minimize their exposure to high-density foods in all parts of their lives: in their cars, at work, at home. The third group continued to receive the Slim-Fast meal replacements for one meal and one snack per day; the fourth group switched entirely to conventional foods. The approach in both the third and the fourth groups left some things to chance—the same vending machine would be in your office when you returned from the study as when you began it—but people changed, say, the lunches that they brought to work and the aisles in the supermarket that they walked down first.
The researchers tracked each participant’s weight (along with a number of other measures, including blood pressure, hemoglobin, waist circumference, physical activity, and home food environment) at three points in time: twelve months, twenty-four months, and thirty-six months after the start of the study. At the beginning, the groups didn’t differ in weight. By the end, however, stark contrasts had emerged. One year out, all the groups were still holding relatively steady. At twenty-four months, the group that was still practicing meal replacement on its own had gained back an average of three pounds, and the control group had gained back five. But the groups that had learned to create a less energy-dense environment had gained less than a pound. When the study came to an end, after thirty-six months, the differences were even more pronounced. The control group had gained back an average of eleven pounds and the meal-replacement group had gained back five. But the energy-density-centric group, which had both learned to replace all of its food with lower-calorie alternatives and switched entirely to conventional foods instead of meal replacements, had gained back only a pound.
No cue is unchangeable. Altering the environment in which you live and work, Lowe suggests—shopping for less-energy-dense foods, putting the Doritos out of reach on the top shelf, changing your commute so that you don’t drive by the doughnut shop—can go a long way toward changing the patterns of hunger that have become ingrained in your routine. When it comes to what we eat, we should be far less concerned with how we feel and far more focussed on—and wary of—when, where, and how we eat. As the English professor and famed aphorist Mason Cooley once remarked, “I pursue pleasure, but stingily, suspiciously.”
Photograph by Andrew Harrer/Bloomberg/Getty.
