Do Rats Yearn for Chocolate Cake?

When I hear the word "craving" it conjures up images of pregnant women eating cottage cheese and peanut butter on toast. I think of people doing crazy things in order to obtain a meal, a dish, a food item that will hit the spot right then and there. Maybe this is because I encountered my first craving anecdote through the Brothers Grimm. Okay, I'm a little odd. But do you remember the story of Rapunzel? What got her in that witch's tower letting down her golden hair was a craving of her mother's.

Rapunzel's mother and father lived next door to a witch who had a bountiful garden. One day, before Rapunzel was born, the wife saw some lettuce that the witch was cultivating. The woman had such a strong desire for it, she could eat nothing until she had some. Her husband, distraught with fear for his wife's health, decided to climb into the witch's garden at night to steal some of the lettuce, no matter the risk. He came back successful. The wife made the lettuce into a lovely salad and ate it up. Three days later the craving came back. The wife wanted, needed, had to have more lettuce. She pestered her husband to no end until he climbed back into the witch's garden for more.

This time, however, he was caught. The witch, instead of killing the poor thief, made a deal with him. She gave him and his wife all the lettuce they wanted in exchange for their first-born child. When a baby girl was born to the unlucky couple, the witch whisked her away and named her Rapunzel, a German word for lettuce.

While I can't exactly relate to the woman's impulse to risk her husband's life for lettuce, I can honestly say there were times in my life when I would have crawled through a witch's garden for a really great brownie sundae. And I suspect I'm not alone. Dr. Harvey Weingarten, Professor of Psychology at McMaster University in Ontario, Canada gained notoriety in his field through a series of surveys he conducted on cravings. "What struck me was how common the experience was and how ubiquitous it was. Most people have these feelings, understand what they are, recognize that they are different from hunger. It was surprising to me how little we understand about the concept given how powerful these descriptions were." All of the experts on food cravings I talked to agreed. Weingarten summed up the conclusions of many of his colleagues: "I think the whole question of where food cravings come from is an important question and one that we don't have a good answer to."

But ask an average American which foods he or she craves the most, and your answer will most likely be an item full of sugar. Why is that? Studies by scientists who study this sort of thing have shown that there is a general preference among humans for sweet foods and drinks. Non-humans that show a preference for sweets are horses (like Mr. Ed), bears (like Winnie The Pooh), ants (think picnic), and lab rats (go figure). Professor Linda Bartoshuk teaches otolaryngological (ear, nose and throat) surgery at Yale University in New Haven, Connecticut. She's also trained as an experimental psychologist. "Taste is absolutely hard-wired into us from birth," she says. Babies are born loving sweet and hating bitter. There is an evolutionary basis for our rejection of bitter: bitter is typically a signal of poison. On the other hand, mother's milk is sweet."

Sweet foods and drinks have high concentrations of sugars and therefore calories. Calories are important to survival and were especially important to early man who didn't have a 7-11 on every corner. Preferences for sweets attracted man to ripe fruits which provided him with sugar, vitamins, and minerals necessary to body function and growth. It's only natural that we should love and crave those foods which make our bodies feel good and energetic.

But what about cravings for potato chips and pretzels, snacks full of salt? Certainly no one is a stranger to that sensation. Professor Bartoshuk has this to say about babies: "They show a liking for dilute salt and a disliking for strong salt. And [sodium] is the most important mineral for our muscles." Our salt cravings, as with sugar ones, seem to have a strong base in genetic predisposition. As Bartoshuk pointed out, sodium is essential for survival, so it's better for our bodies to have too much rather than too little. Because of this, our bodies have figured out how to assure a proper intake if our levels are low. A study done with lab rats demonstrates that rats' (whose biology is similar to humans) preference for salt increases following sodium deprivation. After being deprived of salt for 10 days, the rats were less sensitive to the taste of salt, therefore they ate more of it, giving their bodies what they most needed.

We crave foods like spinach, broccoli, red meat, oysters, or shrimp for similar reasons. "Taste is linked to body needs. If a nutrient is needed in your body, your brain tells you to go out and get it," says Professor Bartoshuk.

Paul Rozin, Experimental Psychologist at the University of Pennsylvania, lived up to his title by feeding rats food lacking thiamine. After they were deprived of thiamine for a time, he then gave them dishes of thiamine-rich food next to dishes of their original nutritionally incomplete food. The rats ate only the new thiamine-laden food. Seems they only liked the food that made them feel better. Rozin called this urge specific hunger. He proposed that rats and humans show high responsiveness to the consequences of their diets and are very good at selecting nutritious foods for themselves.

Cravings can also be based on what we've just eaten. Scientists have shown that ingestion of certain types of foods can automatically affect a person's preference for other types of foods. If you had mostly carbohydrates like donuts for breakfast, you'll want more proteins like meats and cheeses for lunch.

All of this sounds good, almost as though if humans were left to their own devices they would have the perfect diet. But the truth is, while animals appear very good at selecting foods that provide most of the essential nutrients, humans, given a wide selection of foods to choose from, tend to consume too much salt and sugar and not enough of other essential vitamins and nutrients.

And while much of the scientific writings on cravings purport the idea that biology directs desire, just as much writing exists which seems to support the idea that cravings are psychological in nature. "Cravings are something we [scientists] think we understand, but they are hard to define," says Bartoshuk. "Is craving really separate from liking? We know a great deal about liking." We know a great deal about liking because scientists have typically researched the subject of cravings through interviews with humans and experiments with rats. But there's an obvious shortcoming here: "For humans cravings are an emotional experience, and we simply don't know how a rat feels," says Dr. Weingarten.

One empirical study done on cravings in humans (one of the few) disputes the idea that cravings are biologically based. Paul Rozin, the thiamine-deficiency guy, conducted an experiment with people who consistently craved chocolate. After they experienced a craving, he gave them one of two treatments. The first treatment was a chemical cocktail that mimicked the chemicals found in chocolate. Chocolate contains phenylethylamine or PEA and serotonin, which the brain produces when we're feeling good. Eating chocolate also causes our brains to release endorphins and encephalins--mental opiates.

The second treatment was a fake chocolate bar with none of pharmacological properties of chocolate but all of the sensory properties. It looked, smelled, and tasted like chocolate. It even had the same mouth feel as chocolate, but none of the chemicals in real chocolate. Which treatment do you suppose satisfied his subjects the most? The fake chocolate bar.

Says Dr. Harvey Weingarten, "There is a body of literature that is consistent with that observation. It is one of the better scientific experiments we have on food cravings. Scientific in that it goes beyond description." Dr. Kelly Brownell, Professor of Psychology at Yale University, agrees. He says, "Separating the biological and psychological bases of food addictions and cravings is difficult." Brownell runs Yale's Center for Eating and Weight Disorders so he deals closely with the psychological connections humans have to food. "People associate food with good feelings. Food is also used to counteract negative feelings. [Individuals] gravitate toward foods they like and those foods get associated with feeling better."

Research has shown that food paired with pleasurable activities becomes more attractive, especially if food follows the pleasure, (as opposed to preceding the pleasure). That's why reward eating stays with us so well from childhood. Once a chocolate chip cookie is linked with success in grade school, it's hard to break that connection. With every success that follows, you may want to celebrate with a chocolate chip cookie.

Mom isn't the only reason we link food with pleasure as youngens. The way our senses of smell and taste process information has much to do with why we link food to feelings at all. Tastes and smells are gathered through taste buds and nasal tissues. In both cases, the body is processing information about food by absorbing its gaseous chemicals. But most of what we consider to be our sense of taste is really our sense of smell. So much so that what we label artificial flavors are really not much more than artificial odors. This isn't really earth-shattering news to you if you had a fun Biology professor in high school. Remember having to plug your nose and close your eyes and then try and tell the difference between an apple and an onion just by chewing it? Not so easy.

Most of the chemicals we absorb from food are released in the back of the throat as we chew. These retronasal smells float up and are absorbed into our nasal tissue and olfactory bulb which sits just behind the bridge of the nose. Then the olfactory nerve connected to the bulb sends impulses to the limbic lobe of the brain. The limbic lobe is responsible for generating emotions and processing memory. That's where our brains decide whether or not they like a smell. That's how smells get mixed up with and connected to emotions and memory. From there the information is sent to the thalamus of the brain where the smell is finally identified.

This contrasts sharply with the way that information from other senses is processed. The optic nerve, for example, sends impulses to the thalamus of the brain first, and then to the limbic lobe. In other words if we see something, we identify it first and then decide if we like it. When we smell, or by extension, taste something, first we decide if we like it, then we identify it. It goes something like this:

Eyeballs to Brain: hmm, fur, claws, huge, brown. Must be bear. Bear bad. Run!

Nose to Brain: pretty, happy, calming, nice. Is this lavender or rose? Maybe it's gardenia. Can't tell.

That's why smells and tastes are so closely related to events in our lives and our feelings surrounding those events. Let's say for example, the best meal of your life was had when you were 12 years old sitting in the bleachers watching a baseball game with your dad. Life was good, the weather was perfect, your team was winning, dad was spending time with you, etc. That Dodger dog probably tasted sensational. And at the moment you ate it, the taste of the hot dog got mixed up with all those good feelings. Your brain forever linked the sensations together. Now, whenever you're longing for a simple, stress-free hour of life, you have an undeniable yearning for a hot dog with mayo and extra relish.

With all this biology and psychology working against us, how should we deal with the urge to down a gallon of rocky road in the time it takes the L.A. Kings to beat the tar out of the Mighty Ducks? Use your craving as a barometer. Pay attention to it. It's your body's way of telling you that you need something. Maybe it's an extra dose of calcium or some tender loving care. And use your judgment regarding when to indulge. Says, Brownell, "It's fine to listen to [cravings] as long as it leads to a healthy diet, but if you find yourself going beyond the boundaries of healthy eating, then it doesn't make sense."

If you fall into the latter category, you can use the powers of association to help you combat those highly caloric cravings. Perhaps if you're yearning the comfort of chocolate cake you should have a Hershey's kiss and a bubble bath. That way your brain gets the chemicals it wants, your mouth gets the sensation it loves, and your body can experience the relaxation it's looking for through the pleasure of soaking in a warm tub. Together the small dose of chocolate and the long soak may equal the pleasure you normally get from downing eight pieces of Devil's food. In other words, make new connections in your brain. Begin to link food with other easily obtainable, yet pleasurable, actions. That way, if you don't want to indulge in the food that makes you feel good, you can indulge in something less caloric.

It's either that, or become a stockholder in Ben & Jerry's.

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