Has it been scientifically shown why pregnant women have such “weird” eating habits when they are pregnant? I have heard stories of pickles and ice cream, eating soot and sand, and other such odd items. So is there something in the body that causes this?
The short answer to your question is, “No. Science has no definite answer to the problem of odd cravings during pregnancy.”
We need to differentiate between cravings for food substances, such as pickles, and cravings for non-food substances, such as clay and soot.
The craving for clay, dirt, etc. is called “pica”.
http://www.eating-disorder.org/pica.html
Pregnant women and food cravings.
http://www.epregnancy.com/info/nutrition/cravings.htm
Well, shoot me for not having a cite on this, but I know that some biologists believe that food aversions during pregnancy are the body’s way of avoiding things that may have a higher likelihood of bringing harm to the fetus. They’re not sure why, or why not all women have the same aversions. I wish I could remember more details on this, it was quite interesting to read about at the time.
Given all the other things that change/go haywire, I would have been surprised if the appetite remained untouched by pregnancy.
Eeeee, I love the Internet. 
http://www.as.ua.edu/ant/bindon/ant570/Papers/Edwards.htm