Jelly Roll is sharing the secret sauce ... 'cause it looks like running and exercise are a big part of why he's been able to shed a couple hundred pounds and keep the weight off. Check out this video of the "Bloodline" singer out for a jog Tuesday morning in Hollywood ... it looks like he's working up quite the sweat and getting his heart rate up. Jelly had a couple jogging buddies with him too ... seems he got his own little run club here. If this is a preview of what's to come on Valentine's