Parents bringing up my son's weight gain

My 16 year old has put on a bit of weight that last few months. He hyperfixates on foods because he's ADHD and on the spectrum. He has been obsessed with making hot chocolate and he uses a recipe that has sweetened condensed milk. So not super healthy but for the most part he's healthy. I cook foods I know he will eat but make it healthy. And he's very active because he plays hockey. I think he's put on less than 10 pounds. I'm thinking it's the hot chocolate because he makes himself a cup every night to play fortnight or FaceTime with his best friend. I'm not concerned. No one is. My parents are make comments but not even outnod concern. Just to be rude. Saying hea chunky and he bettee be careful because his girlfriend may leave him now that hes chunky. They bring it up every time and it really hurts his feelings. I was always taught to respect your parents but ive kindly asked several times to stop bringing up his weight because it hurts his feelings and it hasn't stopped.