The best that you can do is to try and offer your child foods from all five major food groups (grains, fruits, vegetables, milk, meat and beans) at every meal.
It may not always be possible for you to get him to eat the recommended amount from each group every day, but if you keep a healthy variety of foods available, he will eventually get what he needs over the course of a week or two.
It’s a good idea to get him off to a good start in the morning with a bowl of cereal, milk, and fruit or fruit juice.