We've all heard the expression, "an apple a day keeps the doctor away," but researchers say that old adage may have more validity than many people realize.

From the days of Hippocrates "let food be thy medicine and medicine by thy food," nearly 2,500 years ago, food has been valued for its health-enhancing benefits. In recent years, there has been a growing interest in how specific foods can act to enhance our health, how components in foods can benefit us physiologically and how foods can be enhanced or fortified for improved health benefits.

The term "functional foods" was first introduced in the mid-1980s in Japan to identify processed foods that contain ingredients or components that, in addition to being nutritious, aid specific bodily functions. Currently, Japan is the only country that has a specific regulatory plan and approval process for these foods.

In the United States, the term "functional foods" is often used to identify raw, unprocessed foods that have health benefits beyond basic nutrition.

Examples include fruits, vegetables, and whole grains. Research has found that biologically-active components naturally occurring in these foods may have the power to improve our ability to fight disease. In some cases, they may actually be able to reverse the damage from disease in our bodies.

An increasing body of research indicates that the specific health benefits of these foods may give us the power to have greater control over our overall health, simply by increasing the amount of these functional foods in our diet.

Researchers working with the United States Department of Agriculture have spent the last several years exploring the benefits of a variety of unprocessed foods.

A study at Florida State University is exploring the value of apples and dried plums in preventing and even reversing bone loss caused by osteoporosis. In this study, women who added 10 dried plums to their daily diet improved their bone density by three percent or more.

Other foods showing promise for their disease-fighting power include apples to increase good cholesterol, watermelon, which has been shown in research to improve circulation, flaxseed, shown to prevent formation of arterial plaque, and soy, for improved joint health.

Among the questions that researchers still haven't answered: how much of these foods do we need to eat to get the most benefit? Future research may provide some answers.