The Craving Brain
“All I want is a huge steak. I must need more iron.”
Chances are you, too, have uttered similar words, and quickly proceeded to a local steakhouse for dinner.
For years, popular belief has held that our cravings indicate what is lacking in our diet, that cravings are our bodies’ way of telling us what they need. While not entirely false (there is research connecting cravings to certain nutritional deficiencies), it is not the whole story.
Most of us have food cravings. In fact, 97 percent of women and 68 percent of men who participated in a study published in the journal Appetite reported experiencing them. Cravings are motivational states that give us the urge to seek out and consume a particular food. You know the feeling—no matter what you eat, you’re not satisfied until you eat that one, specific snack.
Some cravings shed light on what’s missing from our diet. A desire to chew ice, for example, has been linked to iron deficiency. If you are severely lacking in sodium—and few Americans are—you will seek out salty food. But plenty of people who eat high-sodium diets still crave potato chips and popcorn. And if our bodies could so easily tell us their nutritional needs, most Americans would have overwhelming hankerings for kale and brussels sprouts.
They don’t, of course. Professor Susan Roberts, director of the Energy Metabolism Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging (HNRCA) at Tufts, has researched the kinds of foods that people crave most often. In a study she conducted with 32 overweight women who were put on a diet, some of the most commonly craved foods were salty snacks, such as chips and french fries, or sweets that were high in sugar and fat, such as chocolate. The most identifiable thing about the foods people crave, she says, is that they are high in calories.
A monotonous diet—and not a nutritional gap—may be more to blame for your yen for a certain food. In a study published in the journal Psychology & Behavior, healthy young adult men and women followed a diet that met all of their nutritional needs but consisted only of nutrition shakes for every meal for five days. People on this one-note diet reported significantly more cravings than they did on a varied diet.
In fact, some research shows that cravings have less to do with biology and more to do with psychology. In a study published in NeuroImage, researchers used MRIs to investigate which areas of the brain are involved in food cravings. Participants were given a nutritional drink (to eliminate hunger during the test), and then asked to think about the taste, smell and texture of a favorite food to prompt a craving.
The MRIs, completed during the induced cravings, showed that the parts of the brain involved in food cravings—the hippocampus, caudate and insula—are identical to those involved in drug addiction. The hippocampus is important for memory, which helps reinforce the reward-seeking behavior that causes us to crave. The caudate also plays a role in these reward mechanisms, and it helps us to form habits, including food-related ones. The insula contributes to the emotional connection between food and cravings.
Triggers of Yearning
Hormones are also involved. As an enjoyable food is consumed, the pleasant feeling of the experience is determined in part by hormone receptors. Over time, these receptors may become less sensitive to the hormones produced when we enjoy a particular food. Eventually, we may need to consume more and more of that food to have the same pleasant experience, similar to the reward circuit seen in drug and cigarette addictions.
It seems that various mechanisms, including hormones and memories, create a Pavlovian response—a sensory cue that causes us to crave. Everyone knows that food is strongly tied to our emotions and memories. This is why a simple image or smell—such as the aroma of baking bread or a photo of a Thanksgiving turkey in a magazine—can cause us to crave a food.
Other things that can send you on an M&Ms run to the vending machine include stress, being in a particular place and reaching a particular time of day. Perhaps not surprisingly, research done at the Medical University of South Carolina and the University of Chicago indicate that these conditioned responses are stronger when we are hungry or dieting.
But do those diet-induced cravings stick around? Maybe not. Research from the HNRCA suggests that cravings may peak during a diet. In a study published in the October 2013 issue of Appetite, participants reported the frequency and intensity of their cravings during a weight-loss program. At the beginning, they reported desiring sweets, carbs and fast foods. However, as participants lost weight, their hunger levels decreased, along with their cravings.
The good news? Understanding that memory and hunger have such large roles in eliciting cravings makes creating a toolbox to manage them that much easier. Next time you have a craving you want to beat, try one of these tricks:
Picture, if You Will
How many times have you lost focus on a task because of an intense food craving? Cravings are shown to interrupt cognitive functioning, partly because they use the same parts of the brain. In other words, you can’t focus on writing that important email because your craving is monopolizing the machinery.
Try beating the craving at its own game. Cravings use working memory, specifically the parts of the brain involved in sights and smells. Visualizing a vivid picture, such as a detailed rainbow, uses that same working memory. A study at McGill University showed that engaging in memory activities that use the imagery sections of the brain reduced cravings. Using imagery was key: Visualizing a favorite activity worked for the participants, while saying the alphabet backward did not.
Smells are strongly tied to our memories and emotions. When you smell something that is associated with a happy time, the brain perks up. The smell cues a desire to experience the pleasure again, and we may consequently crave an associated food.
Fortunately, we can outsmart our brains here, too. It seems that smelling a nonfood odor may help to defeat that craving. A study from Flinders University in Australia showed that after smelling jasmine, college-aged women reported their craving for chocolate lessened. The theory is that smelling a pleasant—but not mouth-watering—odor may once again monopolize the working memory.
Just Run Away
For this trick, you can accomplish two healthful things at once: calm the craving and get in a workout. A British study in the journal Appetite showed that women who walked on a treadmill when a chocolate craving hit reported a reduction in their desire for the sweet. This supports the idea that engaging in any physical activity will help curb cravings.
The Chosen Few
Roberts suggests including only a few unhealthy items in your diet to help control cravings. “Pick the ones that you love and have [just] them, not a wide variety. And then have them occasionally, not all the time.”
In fact, surrendering every now and then may be beneficial—if you do it the right way.
“The best thing is to have a similar flavor that addresses the cravings, but in a food that is more satisfying,” says Roberts. She explains: “Our hypothesis is that cravings are maintained by the neurological reward that you get from ingesting a lot of calories. So when you have a lower-calorie, more slowly digested food, the metabolic stimulus that maintains the craving is reduced.”
The next time you just have to have chocolate, she suggests melting a small piece of it over some high-fiber cereal: “You use less chocolate and fill up on fiber.”
Katie Fesler is a second-year nutrition communications student at the Friedman School. A version of this article first appeared in the Friedman Sprout.
I Could Really Go For…
Cravings may be the price we pay for living in a land of plenty.
“In this country, there are so many options in our lives and in the grocery store. How do we make the decision about what to consume?” asks Tufts psychologist Marcy Goldsmith, J78, G01, G04, a lecturer in psychology in the School of Arts and Sciences.
Cravings—an extreme desire for a particular food—may be one way of making choices among an overwhelming number of edible options. And, she adds, these choices are hardly arbitrary. They are influenced by myriad psychological cues that affect us on both the conscious and subconscious levels.
What may start as a mild desire for a particular food may get stronger if we’re not able to have it immediately, or if we think we shouldn’t let ourselves eat it: It’s too fattening, too high in salt, too rich. So when we actually get to eat whatever’s been on our mind, we feel particularly gratified, because it’s been the focus of our attention for so long.
Then we begin to associate the food with intense gratification. Next time that food comes to mind, “we put a label on it and define it as a craving,” says Goldsmith, who teaches a seminar in nutrition and behavior.
Many times, though, cravings are learned behaviors, triggered by situations: You go to the movies, you crave popcorn. Or you’re subject to an effect known as priming, when a decision or action is influenced subconsciously by something you have been exposed to.
If you see beautiful pictures of food in a magazine, “it’s going to put the thought in your mind, ‘Oh, I should have that,’ ” says Goldsmith. “If it’s repeated enough, it’s going to create an external stimulus—the more you don’t have it, the more you’ll want it.”
Product placements on television rely heavily on the priming phenomenon, Goldsmith says. It’s no accident that the judges on American Idol are seen drinking large cups of Coke, or those on The Voice are sipping Starbucks; the food companies hope your brain will link their beverages with the good feeling you have watching the show. “If I have a positive association between Starbucks and the show I’m enjoying, next time I’m near Starbucks, I’m going to say, let me go get some—I must be thirsty,” Goldsmith says.
Cravings are also culturally driven. In the United States, no food is considered more crave-worthy than chocolate, especially among women. Even the idea that women are physiologically driven to crave chocolate when they’re premenstrual has a lot of cultural acceptance. Yet women from other cultures do not report similar hankerings, researchers have found. And a 2009 study of pre- and postmenopausal American women conducted at the University of Pennsylvania found that self-reported chocolate cravings did not appear to abate after menopause to the degree that would be expected if the cravings were hormonally driven. —Helene Ragovin
Untangling what’s behind a craving for certain foods—whether it’s chocolate chips or potato chips—is one thing. But what about the desire to eat things that aren’t foods? The annals of medicine, literature, history, anthropology and psychology are peppered with examples of people who eat items as varied as dirt, clay, paper, plaster, laundry starch, spoons or nails.
The general term for eating nonfood items is pica. According to the National Institutes of Health, pica occurs more often in young children than in adults, appearing to some degree in 10 percent to 30 percent of children ages one to six. It’s also observed more often in pregnant women than in the general population.
A more specific phenomenon is geophagy, the eating of earth, soil or clay. Its practice has been recorded worldwide and is noted as far back as the writings of Hippocrates. In modern times, it has been regarded from various perspectives as “a psychiatric disease, a culturally sanctioned practice or a sequel to poverty and famine,” write the authors of a history of earth-eating that appeared in the Journal of the Royal Society of Medicine in 2002. An analysis by a team of biologists in 2011 suggests that geophagy helps protect the stomach against toxins, parasites and pathogens.
“We hope readers agree that it is time to stop regarding geophagy as a bizarre, nonadaptive gustatory mistake,” wrote the lead investigator of that study, Sera Young of Cornell University.
Indeed, Tufts anthropologist Stephen Bailey points out that in American culture, people consume stomach-soothing products that contain calcium carbonate or bismuth compounds—minerals and metals that would not ordinarily be considered food.
In fact, the very idea of what is considered food differs from culture to culture, says Bailey, an associate professor in the School of Arts and Sciences. In many places where earth or clay are eaten, the substances are gathered, prepared and consumed in a specific, often ritually prescribed manner.—Helene Ragovin
These articles first appeared in the Winter 2014 issue of Tufts Nutrition magazine.