Year old boy only 16 lbs?

Okay so asking for a friend. She goes to her pediatrician but doesnt seem like they're doing much. I told her to get a second opinion, but her baby boy is about to turn 1 on the 28th. He is 16 lbs and at his recent Dr. Appointment he lost 3 oz. She said he's not really interested in eating. He is super active. My baby boy is the same height as him but weighs a couple pounds or more than him and my baby is only 7 months old. Has anyone experienced this with their babe before? I've heard it could be normal. But just doesnt seem right.