My 13 year old som struggles with weight

My husband any myself workout regularly and have for years. I eat clean 80% of the time. Hubs eats what he wants. My son is overweight – yes maybe he’ll have a growth spurt as his feet are size 12 and hasn’t hit puberty yet but its his eating and lack of desire to move his body that concerns me. He’s addicted to carbs & sugar and at an age where I can’t moniter what he eats all the time. I know he’s self conscious and doesn’t like it. A couple weeks ago he sent me a text when I was at work “Mom, I’m so tired of waking up every morning and seeing how big I am. Will you help me workout?” Tears of joy. Only to find out he’d texted Dad a half hour later ro ask him to bring home a BigMac and fries from McD’s. How can I help him without causing more harm?