Nearly everyone gets food cravings from time to time. Pregnant women are famous for their midnight yearnings for pickles and ice cream. And the desire for chocolate is the stuff of legend.
It's tempting to believe -- as many people do -- that cravings are the body's way of telling us we're lacking a certain nutrient that the food we crave can supply. Chocolate, the belief goes, might soothe a broken heart by replacing compounds lost in oceans of tears. Pregnant women might crave ice cream because they need calcium, or pickles because they lack sodium.
Pregnant women rarely crave fruits and vegetables. More often, they yearn for foods that are very sweet, spicy or salty. From an evolutionary standpoint, this makes sense. A craving for highly palatable foods may have been nature's way of boosting calorie intake, ensuring a healthy pregnancy.
But other kinds of craving make a lot less sense at face value. Some people, for example, get hankerings for things that aren't really considered foods at all -- such as ice, chalk or cornstarch.
The desire to eat non-food items is called pica -- from the Latin word for magpie, a bird known for its indiscriminate feeding habits. Pica is a complicated condition because there are both cultural and nutritional issues associated with it.
In some cultures -- both inside and outside the United States -- it is not uncommon for women to consume clay or dirt during pregnancy. In the Deep South, some people believed that it would relieve the nausea that comes with morning sickness. In some cultures (in Kenya and Uganda, for example) earth-eating, or geophagia, may also have ceremonial or religious purposes.
But there are also numerous case reports of pica that were associated with mineral deficiencies -- especially of iron, and possibly zinc. Iron deficiency is not uncommon in women of childbearing age, particularly during pregnancy.
Because of these various contributing factors, there has been a longstanding debate in nutrition research over the relationship between pica and nutrient status. Some argue that pica causes a nutrient deficit: Eating several cups of cornstarch at a sitting, for example, could bind up dietary iron, making it unavailable to the body. But others argue (and most evidence suggests) that pica frequently is caused by a deficit -- specifically, of iron.
It's hard to get a handle on how prevalent pica is among adults, since many people are reluctant to reveal the behavior to their healthcare provider. It may appear in as many as half of those with iron deficiency, and has been reported in about 20% of pregnant women. One recent study in France found that among 79 patients with iron-deficiency anemia, 44% reported the regular ingestion of non-food items (mostly clay or ice), while only 9% of non-anemic subjects in the control population reported this behavior.
One of the most common forms of pica is ice-eating, or pagophagia. Ice-cravers have been known to eat the frost from the refrigerator or make midnight raids of the convenience store, consuming volumes of ice in the car before they even get back home. Ice-eating is often associated with iron deficiency.
It's not clear why people with anemia develop this craving: Clearly, ice doesn't supply iron or affect nutrient absorption. Some people with iron deficiency suffer from tongue irritation, so it could be that ice-chewing is soothing. Yet whatever the reason may be, the behavior usually goes away when someone's anemia does.
Clay, starch, ice and earth are some of the more common items consumed by pica sufferers, but there are case reports of compulsive eating of more unusual items including cigarette ashes, toothpicks, athletic socks, dust and burnt matches. Depending on the item being eaten, pica could lead to health problems such as lead poisoning from paint chips, constipation from starch or clay intake, or parasites from earth.
Munching on a few ice cubes on a hot day should be no cause for alarm. But if you find yourself frequently sitting down with a couple of trays' worth -- or if you feel compelled to eat things you know you probably shouldn't -- a check-in with your doctor is probably in order. If iron deficiency is discovered and can be resolved with treatment, the cravings will likely diminish quickly.
Susan Bowerman is a registered dietitian and assistant director of the UCLA Center for Human Nutrition.