I don't think yours is underweight, some of the one's I've seen seem a bit overweight/chubby !! Might also be females laying eggs, though..
While the smoothies are the healthiest and perfectly fine on their own (from what I've been told) I do believe the bugs pack on the weight faster. But then again, no need to rush, they live for a long time so letting them grow slow and healthy can't be a bad thing![]()