I get cramps all over my body since I started high blood pressure meds four years ago. They're horrible: quads, hamstrings, calves, abdomen, tongue (I kid you not). Your likely culprit is an electrolyte imbalance (especially since you're exercising/dieting pre-op and no doubt loosing a lot of fluid). Calcium is the easiest to rectify (chew on one or two calcium-added Tums). No-Salt is a potassium salt (and safer than a supplement since potassium is fat-soluble and stored in your body) and should help with potassium intake. Neither of these helped me (again, the meds). I finally realized that magnesium and manganese are also electrolytes. Now I take a magnesium tablet once a week, which seems to help.
My primary physician also suggested "No cramps" or something like that. They're OTC quinine tablets. I take one if a really bad cramp starts up. They work, but I always wonder if they really work or if it's the placebo effect. I find that drinking something like sugar-free Gatorade helps just as well. Hot compresses help to loosen up your muscles.