I need help motivating my son to eat healthy and exercise

Offer an incentive he wants for going out for and sticking with a sport of his choosing. Get him a bike and have him run a few errands for you a couple times a week, (like drop off some dry cleaning at a place a mile or so away) so he gets exercise. On top of that, he might appreciate the extra vote of confidence in you asking him to take on more responsibilities. (and if not, well, make him do it anyway. Call it his way of earning his keep )

Stop buying soda and chips and junk (if you do) and keep the fridge and cupboards stocked with low-cal snacks he likes. Encourage fruit, hummus and vegetables for snacks, and research low-cal versions of his favorite meals.

Is skipping Grandma's house and going straight home an option? He's probably old enough to be by himself for a few hours.

Any fun activities in the area you could sign him up for? Swimming lessons, rock climbing walls, karate? Standard team sports like soccer or basketball might just be uncomfortable and embarrassing if his is really out of shape compared to his peers.

I know some will disagree, but I think he is old enough to have an honest discussion with you. Just tell him you love him and want him to be healthy and ask his opinions on what can be done differently. The focus doesn't need to be weight, just health. Obviously, if he is really sensitive about it that might not work, but I could have handled that discussion at 14.

I'm going to be the unpopular opinion and say that it's not really your business what he looks like and that your harping on him, his weight and his looks WILL ALMOST CERTAINLY do more harm than good and not motivate him to do anything other than hate himself and possibly have a very negative relationship with food

My 15yo son also became slightly overweight this year. I started taking him with me when I went running, and we started talking a lot IN GENERAL about healthy lifestyles, why it's important to invest time in yourself and your physical upkeep, and the benefits of regular exercise. We started out exercising very slowly. We did fun things like plank challenges that started out very simple. We started watching organized sports and discussing the positives of exercise - look how much more energy we have! Look how much better you're sleeping! Did you know running makes your heart stronger? Check out those bicep muscles you're getting! Etc. I couched it all in terms of fun and accomplishment.

Now he of his OWN FREE WILL comes with me on my runs and asks questions about nutrition, health and fitness. He is interested in martial arts now - that's not something I pushed him into, just something he developed out of his own desire to be active. I made it about setting a positive example for a healthy, fun lifestyle. Today we both "graduated" from the Couch to 5K program and he did a little victory dance, he is so proud of himself for it. Going for walks/runs together is also a great parent/kid bonding time, out getting some fresh air and enjoying nature together and carving out some quiet time.

Had I harped on his looks or his weight or nagged him about his eating habits, I would have only alienated him and made him feel bad about himself. Instead, I didn't make it about HIM.

Teenagers are insecure enough as it is, they don't need our help to magnify that.