Do Rats Yearn For Chocolate Cake?

To me, the word “craving” conjures up pregnant women eating cottage cheese and peanut butter on toast. I think of people doing crazy things for something that will hit the spot right away.

Maybe this is because I encountered my first craving anecdote in the Brothers Grimm. Remember Rapunzel? And how she ended up in that witch’s tower with her golden hair?

Rapunzel’s mother and father lived next door to a witch who had a bountiful garden. One day, before Rapunzel was born, her mother saw some lettuce there, and she wanted it so badly she couldn’t eat a thing until she had some. Her husband feared for his wife’s health, so he climbed into the witch’s garden at night and stole some of the lettuce. His wife made it into a lovely salad and ate it up.

Three days later, the craving came back. She wanted, needed, had to have more lettuce. She pestered her husband until he climbed back into the witch’s garden for more.

But this time, he was caught. And instead of killing the poor thief, the witch made a deal with him. He and his wife could have all the lettuce they wanted . . . in exchange for their firstborn 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.

I can’t exactly relate to the woman’s impulse to risk her husband’s life for lettuce, but 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. Harvey Weingarten, professor of psychology at McMaster University in Hamilton in the Canadian province of Ontario, gained notoriety in his field through a series of surveys he conducted on cravings.

“What struck me was how common the experience was,” he says, “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.”

Linda Bartoshuk teaches otolaryngological (ear, nose and throat) surgery at Yale University in New Haven, Conn. 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 bitterness: It’s typically a signal of poison. On the other hand, mother’s milk is sweet.”

Hundreds of thousands of years ago, when there wasn’t a 7-Eleven on every corner, the preference for sweet flavors attracted our ancestors to ripe fruits, which provided them with valuable vitamins and minerals, not to mention the calories necessary for sustaining life. It’s only natural that we should love and crave those foods that make our bodies feel good and energetic.

But what about the common craving for potato chips, pretzels and other salty snacks? 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.”

So our salt cravings, like our sugar cravings, seem to have a metabolic and genetic base. As Bartoshuk points out, since sodium is essential for survival, it’s better for our bodies to have too much of it, rather than too little. To assure that we get our minimum of salt, our bodies have developed a simple signal: craving for salt.

A study done with lab rats (whose biology is broadly similar to ours) shows that their preference for salt increases when the level of sodium in their bloodstream drops. After being deprived of salt for 10 days, the rats were less sensitive to the taste of salt--so they ate more of it.

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 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. Rozin calls this taste for needed nutrients specific hunger. He proposes that rats and people are highly responsive to the consequences of their diets and very good at selecting nutritious foods for themselves.

Cravings can also be based on what we’ve just eaten. Studies have shown that eating certain kinds of foods can automatically affect your preference for others. If you had mostly carbohydrates (say, doughnuts) for breakfast, you’ll want more proteins (meat, cheese) for lunch.

All this has an encouraging sound, as if we would have the perfect diet it we were just left to our own devices. But the truth is, while animals appear very good at selecting foods that provide most of the essential nutrients, we humans, given a wide selection of foods to choose from, tend to go for the salt and sugar, rather than essential nutrients like vitamins.

And while much of the scientific study of cravings supports the idea that biology directs desire, just as much supports the possibility 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?”

An empirical study done on cravings in humans--one of the few--disputes the idea that our cravings are biologically based. 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 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--other natural feel-good chemicals.

The second treatment was a fake chocolate bar. It looked, smelled and tasted like chocolate but contained none of those chocolate chemicals. Which treatment satisfied his subjects the most? The fake chocolate bar.

Blame Mom and Dad. There is research that shows that food paired with pleasurable activities becomes more attractive, especially if food follows the pleasure--in other words, reward eating. Once a chocolate chip cookie is linked with success in grade school, it’s hard to break that connection. Food becomes a way to celebrate a job well done, and sometimes a way to boost self-esteem when you screw up.

So how should you deal with the urge to down a gallon of rocky road? Use your craving as a barometer. It’s your body’s way of telling you that you need something--maybe an extra dose of calcium, maybe some tender loving care.

If your craving leads you beyond the boundaries of healthy eating, though, you can use the powers of association to help you combat that. If you feel like chocolate cake, you could have a chocolate 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 get the relaxation it’s looking for.

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.