Pickles and ice cream. Cheese Whiz on steak. Brownie mix -- straight from the bowl. While these may not exactly seem like gourmet fare, if you're pregnant they can seem like heaven on a plate.

The reason: Pregnancy cravings - those seemingly unquenchable longings for oftentimes eclectic combinations of foods that you might never otherwise even dream of eating!

But what's behind these mysterious food fantasies, and can they ever be harmful? Doctors say the answers depend a lot on what you are craving.

"No one really knows why pregnancy cravings occur, though there are theories that it represents some nutrient that the mother may be lacking -- and the crave is the body's way of asking for what it needs," says Andrei Rebarber, MD, associate director of the division of maternal-fetal medicine at NYU Medical Center in New York.

When that overwhelming desire for pickles or processed cheese hits, Rebarber says it could be the body asking for more sodium. That aching for a Big Mac and a plate of fries may be your need for more protein, sodium, or potassium. The burning in your belly for a double helping of chocolate double latte ice cream may be signaling a need for more calcium or fat.

"It's not that the body actually needs the specific food you are craving, but it may need something in that food. And your taste buds just interpret it as a craving for something specific," says Rebarber.

What's more, many experts say our taste buds do actually play a role in how we interpret our body's needs. Studies show that the high hormone levels present during pregnancy can alter both a woman's sense of taste and smell. So certain foods and odors can not only be more enticing but in some cases more offensive; a problem that often plays out as a pregnancy food aversion.

"Food aversions are most often associated with early pregnancy -- when they are likely to touch off a bout of morning sickness -- with nausea and vomiting," says Rebarber.

While some pregnancy cravings can certainly seem a bit odd, in most instances, they don't represent any real threat to mother or the baby. This, however, can change dramatically, when the craving is for a nonfood item. The condition, known as pica, can lead to an overwhelming desire to consume any number of substances, some of which can be extremely harmful to both mother and baby.