Chemically, I have no metabolism. I am without a thyroid and regular thyroid medication (synthroid) doesn't break down into T3 (the metabolic hormone) for me. So I take T3 synthetically.

To destroy your metabolism for life with a thyroid, you would need to do an extreme starvation, extreme bingeing regiment over a period of time. Your body is amazing in its ability to recover from feast and famine. That what it was designed to do.

There was a study where women were tested for T3 while on low fat and low carb diets. The women on low fat had a 20% decrease of T3 or metablism. On low carb, the women tested a 13% decrease. I wish they would have studied low calorie. But I think it goes without saying that decreasing calories slows the production of T3 so much that the "starvation mode" kicks in and weight stalls. I am sure we have all experienced that when trying to lose weight.

Personally when it comes to calories, I always think this is how I will eat for the rest of life not just until I reach a certain weight. For me, I acknowledge I am overweight but it is only a result of many lifestyle (and medical) issues.

But this is just my opinion. If you feel comfortable eating 1200 for the rest of life... knock yourself out. You know your body better than anyone!

HTH,
Michele