Nutrition plays a central role in a persons over all health, but achieving a good diet is not as simple as it sounds. Eating the right foods and portion sizes are longer is a win-win when it comes to your health, nor does it ensure proper health. 
Over farming, Excessive Food Processing, the use of addative, chemicals, and toxins that contaminates the food supply does not give us the great foods supply and nutrients of yesterday.
It is very important to pay attention to; not only what foods are eaten, but also to how those foods were grown, treated, and prepared before it reached your table. 
We should consume far less fats, animal proteins, and processed foods and more complex carbs, fruits, and veggies. The American diet over the past two decades have been increasingly filled with processed and contaminated foods. As a result we are now suffering with more Allergies and degenerative disases primarily (atherosclerosis, heart disease, stroke, diabetes, and some types of cancer).
The Surgeon Generals Report on Nutrition and Health Acknowledges, “What we eat may effect our risk for several of the leading causes of death.”