What happens to a person's metabolism when they consistently eat too little?

     That said, the point is not to lose weight too fast by radically reducing calories because first and foremost that method is inadequate and generally not sustainable. Secondarily, there is a slight (fairly insignificant in the big picture) metabolism down regulation in response to a very low calorie diet – but – the main reason it may appear to slow down more than it actually does, is because it’s the very low calorie intake that is slowing YOU down. In other words, you become tired driving a reduction in your daily activities, causing you to move less thus burn fewer calories.

 (Take it to the bank message: never blame disappointment on metabolism – no matter what anyone tells you!)