I personally eat very few grains and then only oats or barley about 1/3 cup per day but many days I don't eat any at all.
Wheat, corn etc are not essential to a healthy diet although they are featured on the bottom of the food groups pyramid as essential foods. A lot of pressure has been applied from different agricultural groups to make this so. Grains are relatively inexpensive due to government subsidies. However they don't provide any nutrients you can't get from other foods. There are many researchers that argue that it is grains not saturated fat that contribute to disease. The latest research claiming that wheat may contribute to diabetes. Refined carbohydrates probably do a lot more harm that saturated fat and being overweight is more harmful than both. Maintaining a healthy body weight is ultimately more important than what percentage of the diet is protein, fat, or carbohydrate.
Information from The Nutrition Data Blog