It's because you've got an enemy in your body, and its name is Inflammation. And it's not only responsible for why you feel absolutely horrible, but it can also take the credit for your fouled-up metabolism.
Here's how it happens. When excessive inflammation is present, it causes a cascade of dysfunction in the body, starting with pro-inflammatory cytokines, immune system messengers that become excessively production-happy in the presence of Lyme biotoxins. Then, like an out-of-control battalion, they cruise past the blood-brain barrier and disrupt the production of leptin by occupying its receptor site on the hypothalamus. Leptin is a hormone that's responsible for regulating body mass and storing fatty acids, and when its receptor site is blocked by cytokines, the body responds by increasing its production, in an attempt to compensate. But since the nasty cytokines have occupied the receptor site, all that extra leptin instead floats around the body, where it has the effect of increasing the storage of fatty acids, which translates into, you guessed it, more weight on your bones.
So what can you do? Reducing inflammation is key, but it's not a simple matter. Those who have trouble detoxifying may have an especially difficult time getting rid of extra pounds, since higher levels of biotoxins means increased levels of inflammation, and hence, more weight.
Effectively controlling inflammation requires a dissertation, which I won't attempt to write in this post. But perhaps you can take comfort in the fact that as you heal your Lyme disease, chances are, your weight issues will disappear, too. In the meantime, if you can find a way to control the inflammation while you are treating Lyme disease, this is even better, and not just for reasons of body image. Reducing inflammation accelerates healing, in big ways (see my post later this week). If you have trouble detoxing, I also highly recommend you read Dr. Ritchie Shoemaker's book, Mold Warriors, which discusses ways of lowering inflammation caused by biotoxins (from Lyme and otherwise).