Anon, I am soooooo glad you asked this. SO GLAD! (You may want to faceroll because of my emphatic … emphaticness… on the subject, but just follow my ranting!)
So, lets take a look at what birth control actually does and what effects these things have on the body:
It regulates the release of the hormones that regulate menses
(What does this mean? It means your normal ravenous cravings for potato chips dipped in dark chocolate will subside! If your hormones are normalized then there won’t be the same severe fluctuations that escalate cravings in the first place. It will also help to prevent mood swings and cramping.)
It makes the uterus inhospitable to an egg and to sperm. It makes the mucus of the cervix inhospitable to sperm. It makes the lining of the uterus incapable (or less capable) of implanting an egg.
(What does this mean? For weight gain and cravings… not much, really. There will be a slight shift in the pH of your uterus: think .1 to .3 pH points, but this will not effect other aspects of your body.)
There have been studies done on primates to test the hypothesis that birth control causes weight gain. The results? Hypothesis disproved. (Take a read, ScienceDaily is a great place for science news without needing to know much about the inner workings to understand what’s going on.)
My hypothesis? Women on birth control gain weight due to the comfort factor of being with the same man for a long period of time. Maybe women refrain from going on birth control until they feel comfortable enough in a relationship to stop using other methods of birth control? Comfort with a partner and length of a relationship often result in less active lifestyle, more eating out and more munchie nommies while sitting on the couch together. Then what? Weight gain! The connection is made because it’s a lot easier for people to notice that change in their lifestyle (the starting of birth control) than in the gradual shift to inactivity and munchie noms.
So! Since you are going on BC for health reasons, you definitely shouldn’t have to worry. The first few months you may notice some bloating from water weights, but it will normalize after your body gets used to the shift in hormones.