We all know the classic pregnancy tale of the dutiful husband on a midnight hunt for pickles (or whatever) to assuage his wife's sudden and intense craving.
But the pregnant-pickle story tells another story most of us don't so readily recognize - one that reveals why you crave certain foods, and why you want foods you've never wanted before. What you crave is partly a by-product of what you've failed to get into your system that your body needs - namely increased levels of vitamins, minerals, proteins and even plain old water.
Our stomach and circulatory system don't literally want (much less need) fast food or even pickles... all they need are much simpler bio-molecular structures-- vitamins, minerals, proteins, and fats critical to the healthy development of your child and the maintenance of the placenta.
When your body senses something is lacking in a serious way, all it knows is that it's important that you react by getting those ingredients into your gut ASAP, there is no consideration of what else accompanies those ingredients.
For example, your body needs certain amounts of sodium so a craving signal is sent to your brain. After which point, you experience a craving and must then solve the general "I crave something salty" sensation you're experiencing by assigning the item you think best satisfies your craving, which could range from salty roasted almonds to the infamous pickles-n-peanut butter.
Pregnancy demands that this signaling system not only works well, but that it's running at fult tilt to ensure your baby's nutritional needs are being met at this life-critical stage of their development.
Getting your system into "full-tilt nutrition" mode is the domain of the all-powerful pregnancy hormones, which'll increase the intensity of the craving signal sent from your gut to your brain as well as the psychological sense of urgency in reaction to it, amping your "want" up to a full-blown craving.