As I sat down to write this blog post, I couldn't concentrate. Instead of thinking about cravings, one of the subjects I recently discussed with Marci Pelchat of the Monell Chemical Senses Center, I couldn't stop thinking about my own overwhelming urge to eat some of the homemade peach and berry crisp siting on the kitchen table.
Was my body trying to tell me that I needed the antioxidants in the berries? It doesn't take a Ph.D. to figure out that, in this case, the craving probably had more to do with psychology (namely, procrastination) than biology. But is a food craving ever a message from your body that you are lacking something in your diet?
Other than a few kinds of extreme deficiencies, probably not, Pelchat says. If research animals are deprived of salt, for instance, they will tend to go for food that contains salt. But in most cases, there's not much evidence for the "wisdom of the body" theory of cravings. "I can see the appeal—I'm craving chocolate, I must need magnesium," she says. "I know people are disappointed by that answer."
One exception may be iron-deficient anemia, which is sometimes linked to an eating disorder called pica, in which a person has a craving for ice, dirt or other non-food items. Pelchat related the story of a woman who was in the hospital with both iron-deficient anemia and mercury poisoning; she was eating a box of facial tissues a day. The anemia was brought under control, and the mercury poisoning also resolved. It turned out that, at home, the woman had been buying used paperback books to eat because they were less expensive than tissues—and until a couple of decades ago, mercury was used in the processing of paper.
If it isn't nutritional needs, then, what does cause cravings in average people? Both men and women report them, although women—especially women of child-bearing age—report them slightly more often, Pelchat says. Chocolate cravings appear to decline significantly in women as they age, and many women report increased cravings (especially for chocolate) around menstruation. This all suggests there may be some correlation between hormones and cravings, although the evidence is not conclusive. One study about 10 years ago found no decrease in reported cravings for sweets among women treated with progesterone. It's possible, Pelchat says, that peri-menstrual symptoms, rather than being a cause of cravings, "may be a condition cue for self-coddling, an excuse for indulging."
Despite the lore about pregnant women having bizarre cravings for pickles with ice cream, expectant women don't report a lot more cravings than other women of child-bearing age. The cravings they report, however, are more concentrated among certain types of foods: milky foods, such as ice cream, and sweet and tart foods (okay, like pickles).
My mother tells me she craved spaghetti sauce when she was pregnant—ate it right out of the can—which probably fits into the tart category. But she also developed a powerful aversion to bananas that has persisted her whole life, which is not usually the case with pregnancy aversions, according to Pelchat. Unlike cravings during pregnancy, aversions are probably more connected to odors—some expectant women report a heightened sense of smell, although it's difficult to measure—and to nausea. In my mother's case, it may be that bananas turned into a "learned aversion" (like what might happen after you throw up your hot dog at the fair).
If much about cravings is still a mystery, one thing has been clear in Pelchat's research: a monotonous diet is likely to trigger them. In studies in which participants were fed only an Ensure-like liquid that provided all their nutritional and caloric needs for three weeks (and were required to finish it so they were full), she says, it took only two days for young adults to report huge increases in cravings. They all craved non-sweet foods. "We don't know if it's boredom, or the idea of restriction," she says, "but clearly it isn't nutritional need."