HE needs to help plan the grocery list and help shop. This way....he gets some things HE wants....AS LONG AS they are healthy. ENCOURAGE trying new foods and make SURE you do the same! NO...ABSOLUTELY NO "Yucks". EVERYONE tries a "courtesy bite" reminding them that they don't have to like it but they won't know unless they try.
If they still balk, ask them about something they like. If they like it.....how do they know......they tried it, of course.
Allowing kids to be involved DOES help. Talk about the nutritional value of foods.....why your body needs protein, why good carbohydrates, etc.
DO NOT feed the child high carb meals at night! THIS IS A MAJOR REASON PEOPLE CANT GET UP THE NEXT MORNING. Don't allow him to eat a bowl of cereal before bed. Protein, vegetables and limited whole grains.
Let him help PREPARE. I teach nutrition and cooking to three & four year olds. THEY LOVE to be involved. I have a multitude of kids who've gone from very picky eaters to trying everything and wanting to be a part of planning, preparing, shopping, etc.
hard to get him to do it when he obviously doesn't understand the value. If he doesn't eat or fuel himself properly, he won't perform as well. If there is $$$ involved on your part....uniforms, fees, etc. I'd flat out tell him you're not paying for the program if he's not going to do his part to do his best. This also helps them understand they play a role in the success, not just by participation, but also in making good nutitional choices.
I DO consultation for moms, kids, & families too.