People with chronic obstructive pulmonary disease are often so focused on respiration that other aspects of their health are ignored. That can be a big mistake when it comes to diet.

Good nutrition is critically important in the treatment of COPD because it can have a profound effect on the severity of the disease, experts say.

"We always hope that physicians treating COPD patients refer them to a registered dietitian to review nutrition therapy," says Gail Frank, a nutrition professor at California State University, Long Beach, and a spokeswoman for the American Dietetic Association. "It can make such a difference."

Not that nutritional therapy for COPD is easy. It isn?t. One of the big problems in trying to improve diet is that the symptoms of the disease can make eating healthfully -- or even eating at all -- a challenge.

"It may be difficult to eat," says Frank. "You breathe and swallow through the same tubing system. So you may not want to eat foods that are hard to chew and swallow. Some people can?t swallow liquids well. Liquids can present a problem for people who have nasal tubes or oral tubes or who have oxygen therapy."

Nutritionists often address the needs of COPD patients by examining their body type. Some COPD patients are overweight, for example. This is commonly linked to chronic bronchitis. These individuals often have a problem with fluid retention in their legs and feet.

Being too heavy also makes the heart work harder. And excess abdominal fat can put pressure on the diaphragm, making it harder to draw a full breath.

Other COPD patients are underweight. This body type is more common among people with emphysema. These individuals typically have poor appetites and even begin to lose muscle due to an inadequate caloric intake. Included in this muscle loss are the muscles that aid in breathing.

An inadequate diet often creates serious problems for people with COPD. If the diet is deficient in protein, calories, vitamins and minerals, it?s very hard for the immune system to muster the resources to fight the respiratory infections that plague COPD patients and for it to repair damaged tissue.

Nutritional therapy for COPD doesn?t just focus on food intake to promote weight loss or weight gain, however. The types of foods people eat can make a big difference in respiration, says Frank.

For instance, eating food high in carbohydrates produces carbon dioxide when the food is metabolized. The carbon dioxide is expelled through the lungs.

"The more carbon dioxide you produce, the more demand on the lung," Frank says. "So we generally try to restrict carbohydrate intake in people with COPD."

Many dietitians recommend that COPD patients limit carbohydrate intake to about 150 to 200 grams per day. The next trick is to limit carbohydrates and keep caloric intake adequate.

"You do that by adding more protein or fat," Frank says, adding that patients should first aim to consume about 1 gram of protein per kilogram of body weight. Examine food package labels to find out how many grams of protein are in a serving. To calculate kilograms, multiple pounds by .45. For example, a 150-pound person weighs 67.5 kilograms.

When planning a diet, choose foods that are easy to consume, she adds.

"You want to make sure you are avoiding heavily fried foods, which not only cause a choking problem but take much longer to digest," Frank says. "Nuts, olives and seeds can also cause problems swallowing."

Nutritionists often advise COPD patients to have several small meals and snacks to aid in digestion and to avoid lying down after meals. Some people may also find that they feel better if they avoid gas-forming food, such as broccoli, beans and peppers.

People with COPD also need to pay attention to vitamins and minerals, particularly if their condition is severe and the organs are not functioning well, experts say. Vitamin B, in particular, helps with the digestion and metabolism of fat and carbohydrates. Eggs, beef, yogurt and whole grains are good sources of vitamin B, which is actually many different vitamins. Vitamin A is better to take as its precursor, beta carotene, which is less toxic in large doses than Vitamin A, says Peter Katona, MD, of the University of California, Los Angeles.

Recent studies have found that vitamin A can be extremely helpful in COPD patients who are deficient in it. Individuals should talk to their doctors about vitamin A supplementation before beginning vitamin therapy, however.

It?s also important to drink plenty of fluids to hydrate the body and keep mucus thin. Try to avoid caffeinated drinks, however. Some people may also want to avoid carbonated drinks if they cause gas.

Women with COPD should pay special attention to calcium intake -- especially if steroids are taken as part of their treatment

Finally, COPD patients should strive to plan meals that are satisfying.

"Keeping energy up is important," Frank says. "It?s important to know that food will continue to bring joy, pleasure and nutrition throughout life."