Fresh spring lettuce, succulent fruits in summer, autumn's squash and wild rice, root vegetables in winter. Eating fresh seasonal produce not only is delicious, it is a good way to connect with the rhythms of the natural world. And that, according to Dr. Elson Haas, founder and director of the Preventive Medical Center in San Rafael, California, is essential to good health.

'Your well-being depends upon understanding and integrating your own cycles with those of nature,' Haas writes in his newly reissued book Staying Healthy with the Seasons (Celestial Arts). Originally published in 1981, this classic was one of the first books to integrate Eastern healing traditions with modern Western medicine and helped shape today's burgeoning field of integrative medicine. Haas considers health through the lens of the five seasons (including late summer) and the Chinese Five Element theory, which holds that all energy and substance relate to fire, earth, metal (or air), water, or wood. In the human body, he explains, each element is important for specific body organs, 'which in turn become especially vulnerable with each new season.'

Autumn, the season of the large intestine and the lungs, is the time for concentrating on elimination and cold prevention, as well as building up for winter with proteins, grains, vegetables, nuts, and seeds. Winter's emphasis on the kidney and bladder requires attention to reproductive processes and the warming nutrition of fish, cooked foods, and beans. Spring's dietary emphasis is on citrus, greens, and herb teas because this is the season of the liver and it is all about cleansing. In summer, the season of the heart, it's time to focus on exercise and eating cooling foods like salads, fruits, and liquids. Detoxifying is the core of Haas' approach. 'Most illnesses are a result of excess toxins in the body,' he writes. 'Healing is the elimination or cleansing of these toxins, and then achieving a balance of intake and output.' Unlike fasting, which is defined as water intake only, cleansing is done by drinking only fruit and vegetable juices -- eating no solid foods -- for five to ten days or longer.