According to the Dietary Guidelines for Americans 2005, nutrient-dense foods are foods that provide substantial amounts of vitamins, minerals, and phytonutrients with relatively few calories.  Vegetables, fruits, eggs, meats and nuts are considered nutrient-dense foods, while products containing sugar, refined carbohydrates, and alcohol are not.  The opposite of nutrient dense foods is “calorie-dense foods” or foods containing empty calories, such as soda, processed and refined starch (such as crackers or white bread) and beer.
Large population studies looking at dietary habits found higher rates of obesity and an assortment of diseases in people consuming calorie-dense foods.  It has been hypothesized that eating more nutrient dense foods would result in less calorie intake, which would potentially aid in maintaining a healthy weight.  Unfortunately, human studies in this area are lacking.
However, research suggests that a number of diseases involve the uncontrolled destruction of various cells.  This process is referred to as oxidation.  Oxidation occurs whenever oxygen interacts with another cell; it is ubiquitous and never stops 24 hours a day.  Our body is armed with some natural defenses that usually control harmful oxidized byproducts, but it is the uncontrolled oxidation of cells that creates disease and pathologies.  Foods that contain “antioxidants” prevent the likelihood of oxidation, and potentially decrease the risk of certain diseases, such as cancer, heart disease, Alzheimer’s disease, and Parkinson’s disease.
Antioxidants are found primarily in fresh veggies (especially cruciferous veggies), fruits, nuts, meat and fish.  Each food contains its own amount of antioxidants and other nutrients.  Therefore, an assortment of nutrient dense foods is necessary to get the most beneficial array of nutrients and antioxidants.  Nuts in particular have a variety of nutrients, but their nutrient concentrations vary by type.  For example, almonds are high in antioxidants, while walnuts contain omega-3 fatty acids, which prevent cardiovascular disease and regulate blood sugar.  Both nutrients are needed for optimal health.  Because few foods contain all needed nutrients to live optimally, variety is essential to achieve favorable health.
In general, fresh, locally grown vegetables are the most nutrient-dense of all food groups.  Certain nutrients found in fresh food decreases over time when exposed to light, heat, and air.  For this reason, it is better to ingest foods that are farmed locally and require minimal time from harvest to plate.  After vegetables, the next groups of nutrient-dense foods are fish, followed by meats and various fruits.  A diet centered on a variety of these foods will lead to a healthier you now and for years to come.