My almost 2 year old will only eat 1-2 meals a day. She eats a good breakfast(most of the time), never eats lunch and occasionally she skips dinner. She does eat a banana or cheese or other healthy snack before bedtime though.
I asked our Dr about this since I was concerned. Since she is still thriving and growing quite well- at the 95th percentile on weight (not sure how though) he said not to worry. I also make sure I do feed her balanced meals though when she does eat.
I also help her to get the rest of her fruits and veggies in by giving her V8 Fruit Fusion for her drinks during the day. I do this throughout the whole day. In the morning she will get a half serving of it mixed with water. Then the rest of the day I will put just a very small amount in water to just flavor it up for her and she loves it. At nap and bedtime she gets a cup of milk.
One thing I would suggest though, not sure if you do this or not, is to make sure he is sitting down with you at all meals. Even if he does not eat it is there for him if he wants to. I always make my daughter sit at the table with us even if she doesnt touch her food. I really feel that meals are a great time to connect- even though she doesnt participate except to throw food to the dogs or to babble but it is a practice I want to continue as she is older! Plus, a lot of the time, except for lunch, she will start eatting when we are almost done.
Good luck to you and as long as your son is not withering away I would not worry to much! Kids really know when they are hungry from the time they are born. Remember when they would turn the head to the bottle or breast?!?! This is nothing different! Many blessings to you!