Two things adversely affect your child's health. One is when a nutrient is missing from her diet. For example, a deficiency of iron can lead to iron deficiency anemia. Iron deficiency often results in learning problems and stunted growth.  Low levels of the important mineral zinc can decrease your child's appetite. And a diet insufficient in magnesium can result in weak bones. 

When something in the diet is toxic to your child's system, this can also cause health issues.  For instance, many children are allergic or intolerant to gluten (ingredient in wheat and barley). As a result, they may have digestive difficulties, such as constipation and pain.

Some children react to artificial colors and/or flavors in foods. These children often display behavior issues such as hyperactivity.

There are steps you can take to determine if your child is being affected by either of these issues.

Here is a good place to start:

Artificial Additives and Our Kids' Health