February 2009 Issue

Nutrition and COPD - Dietary Considerations for Better Breathing

By Ilaria St. Florian, MS, RD

Today’s Dietitian

Vol. 11 No. 2 P. 54

A recent survey conducted by the National Heart, Lung, and Blood Institute suggests that despite a growing awareness of chronic obstructive pulmonary disease (COPD), only 64% of respondents had ever heard of it. Yet, according to the Global Initiative for Chronic Obstructive Lung Disease, COPD “is the fourth leading cause of chronic morbidity and mortality in the United States” and an estimated 24 million Americans are affected.1

COPD is a progressive lung disease that makes breathing difficult due to partially obstructed airflow into and out of the lungs. It results from an inflammatory and destructive process in the lungs stimulated by exposure to toxins, primarily due to a history of smoking cigarettes.

Healthy people’s bronchial tubes and alveoli are elastic; thus, when they breathe in and out, they inflate and deflate much like a balloon. In contrast, patients with COPD experience limited airflow through their airways due to either a loss of elasticity and/or inflamed, damaged, or mucous-clogged airways. Because the airways are partially blocked or damaged, breathing becomes difficult, and the lungs begin to lose their ability to effectively take up oxygen and remove carbon dioxide.2,3 “Expiratory airflow limitation” is the hallmark of COPD, and the gold standard for diagnosis is spirometry, which is a simple lung function test that measures how well the lungs exhale.1

Symptoms of COPD include chronic cough, often referred to as “smoker’s cough”; excessive mucous production; wheezing; shortness of breath; tightness in the chest; and a decrease in exercise capacity.2,4 The leading cause of COPD is cigarette smoking; in fact, most patients with COPD are either current smokers or have a history of smoking. According to the American Lung Association, an estimated 80% to 90% of COPD deaths are attributed to smoking, and smoking cessation is the most effective

According to the ADA’s 2008 practice guidelines for COPD, at-risk patients should take at least 1,200 milligrams of calcium and 800 to 1,000 international units of vitamin D daily to minimize bone loss.

A healthy diet for patients with COPD can lead to better breathing and possibly facilitate weaning from mechanical ventilation by providing the calories necessary to meet metabolic needs, restore FFM, and reduce hypercapnia. Carbon dioxide is a waste product of metabolism and is normally expelled via the lungs. However, patients with COPD who have limited and obstructed airflow have a compromised ability to take in oxygen and eliminate carbon dioxide. In patients with COPD, this impaired gas exchange increases patients’ ventilatory demands, as the lungs must work harder to clear excess carbon dioxide. In healthy individuals, increased carbon dioxide levels are easily eliminated.7

The Importance of Proper Nutrition

Proper nutrition can help reduce carbon dioxide levels and improve breathing. Specifically, it is important to focus on the percentages of total carbohydrate, fat, and protein that patients consume to see how their diet composition impacts their respiratory quotient (RQ), which is defined as the ratio of carbon dioxide produced to oxygen consumed. To put it simply, following metabolism, carbohydrate, fat, and protein are all converted to carbon dioxide and water in the presence of oxygen. However, the ratio of carbon dioxide produced to oxygen consumed differs per macronutrient; the RQ for carbohydrate is 1, fat is 0.7, and protein is 0.8. From a nutritional standpoint, this means that eating carbohydrates will yield the most carbon dioxide, while eating fats will yield the least carbon dioxide. That said, prescribing a high-fat, low-carbohydrate diet would reduce patient RQ levels and carbon dioxide production. In fact, patients who have difficulty increasing ventilation following a carbohydrate load or patients with severe dyspnea or hypercapnia may benefit from a high-fat diet.6

A July 1993 study in Chest found that a high-fat diet (55% fat) would be more beneficial to patients with COPD than a high-carbohydrate diet (55% carbohydrate) because it would decrease carbon dioxide production, oxygen consumption, and RQ, as well as improve ventilation. However, there is not a general consensus in the literature to universally recommend a high-fat, low-carbohydrate diet, as it may not be necessary for stable patients and not all patients may be able to tolerate the potential side effects (eg, gastrointestinal and abdominal discomfort, belching, diarrhea). In addition, some patients may have a coexisting heart condition, which could make a high-fat diet contraindicated.6 In fact, 25% of COPD patients develop pulmonary hypertension due to low oxygen levels, which results in enlargement and thickening of the right ventricle of the heart, a condition known as corpulmonale.

Therefore, according to the ADA’s Manual of Clinical Dietetics, it is best to replete energy needs but avoid overfeeding as “excess calories are more significant in the production of carbon dioxide than the