People are nosy and they're ridiculous.
The truth is that with weight removal you will lose some lean muscle mass. This is true of *all* weight removal programs, not just Atkins. However, if you're exercising like you're supposed to be you're building more lean muscle mass than you're losing, and at 300lbs, you've already got a lot of muscle! People don't think like that though. It takes quite a bit of muscle to move a body that size around, but they go back to their alarmist, half-informed,
"I heard it from my brother's girlfriend's sister's friend's half-brother's neighbor's mechanic who saw it on Hard Copy" garbage.
.
Do your thing and as you really start to improve your health and the results are more and more visible all the time, they'll start asking you, just like gman said
Keep on keepin' on!