What are the characteristics of a healthy diet?

The Dietary Guidelines for Americans offer concrete science based information for a Healthy Diet and Lifestyle. Generlly speaking:

• Make smart choices from every food group. Your eating plan should include fruits, vegetables, whole grains, and fat-free and low-fat milk and milk products, that includes lean meat, poultry, fish, beans, eggs and nuts, and that's low in saturated fat, trans fats, cholesterol, salt (sodium), and added sugars.
• Find your balance between food and physical activity, by balancing the calories you take in from food with the calories your spend each day.
• Get the most nutrition out of your calories by choosing nutrient rich foods ( foods with more nutrients and fewer calories) from each food group every day. Pick fruits, vegetables, whole grains, and fat-free and low-fat milk and milk products more often. 

The Dietary Guidelines for Americans, 2010, released on January 31, 2011, emphasize three major goals for Americans:

• Balance calories with physical activity to manage weight
• Consume more of certain foods and nutrients such as fruits, vegetables, whole grains, fat-free and low-fat dairy products, and seafood
• Consume fewer foods with sodium (salt), saturated fats, trans fats, cholesterol, added sugars, and refined grains

The Dietary Guidelines for Americans, 2010 include 23 key recommendations for the general population and 6 additional key recommendations for specific population groups, such as pregnant women. The recommendations are intended to help people choose an overall healthy diet. http://www.health.gov/dietaryguidelines/2010.asp