They say that, ?An apple a day keeps the doctor away.? Good nutrition plays a key role, not only in keeping you from rushing to the medicine cabinet during the season of cold and flu virus, but also in maintaining a healthy immune system. Lacking in one or more of essential nutrients may prevent the immune system from functioning at its peak.

Functioning as a complex web of mechanisms inside the human body, the immune system is designed to protect and defend against millions of invaders such as allergens, bacteria, viruses, and other potentially harmful organisms, collectively known as antigens.

Serving as the first line of defense against these invaders are the skin and the membranes that line the entrances to the body. These entrances are the nasal passages, the eyes, and the respiratory and digestive tracts. If these antigens make it past the skin, they have to face the specialized white blood cells called T-lymphocytes, which continuously patrol the body in search of these body invaders. Other cells that keep the body protected from these harmful germs are B-lymphocytes, neutrophils, and macrophages. B-lymphocytes are special blood proteins that neutralize or destroy germs. Neutrophils and macrophages, on the other hand, scavenge antigens from the blood for delivery to the lymphatic system, which disposes them. It is our obligation to help these cells to function efficiently in keeping our body protected from bacterial infections.

While essential nutrients are critical for the production and maintenance of key germ-fighting cells in the immune system, a balanced diet also has a strong effect on vascular function. Note that the immune system is dependent on blood flow because the bloodstream is the route along which infection-fighting cells travel throughout the body to where they are needed.

There isn't one specific nutrient or food that can easily vanquish the cold germs and flu virus spells. Maintaining a well-balanced diet and keeping a healthy eating habit are your best assurance to keep the immune system functioning properly.

Fruits and vegetables are rich in vitamins A and C. It also has phytochemicals that lend fruits and vegetables their colors. These food groups also contain antioxidants that promote the body's built-in anti-viral and anti-bacterial functions. These nutrients help ensure that the lymphocytes can divide and reproduce properly in response to a virus, and that the neutrophils and macrophages that engulf and kill invading bacteria can do their job.

Maximizing the variety of vitamins, minerals, and antioxidants can be achieved by eating 5 to 9 servings of fruits and vegetables per day. It is necessary to consume two different colors of vegetables and fruits with each meal, and one-third of lean protein.

Include in your diet a generous amount of protein to ensure production of more white blood cells to help combat the invading antigens. The building blocks of all the body's cells, including the cells that power the immune system, are the amino acids found in protein. Protein and amino acids are essential in increasing immune cell proliferation.

Realizing how important the role of nutrition plays in maintaining a healthy immune system can make the trip to your family doctor easily be re-routed to the kitchen instead. Apples, anyone?