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Tuesday, November 15, 2005, 12:00 p.m. EDT
A new study finds that eating mostly meat, refined starches, and sodium may increase the likelihood of developing chronic respiratory symptoms, including chronic obstructive pulmonary disease (COPD). Researchers found that individuals whose diets are rich in meat, refined starches and sodium are 1.43 times more likely to report new onset of persistent coughs with phlegm than those who consume a diet high in fruit and soy.
"Understanding all the contributing factors, including the role that diet plays in the incidence and development of chronic respiratory symptoms will lead to better prevention and treatment of respiratory diseases," said David A. Schwartz, M.D., the director of the National Institute of Environmental Health Sciences (NIEHS), the component of the National Institutes of Health, that supported the study. "We know that cigarette smoking can be a specific cause of COPD, but now we're learning that avoiding certain foods may help reduce chronic respiratory symptoms, both in smokers and non-smokers."
The results appearing online in American Journal of Respiratory and Critical Care Medicine analyzed data to assess the usual dietary intake of 52,325 participants. Although the study was conducted within a Singaporean population, the dietary patterns are reflective of U.S. eating patterns. The study population consisted of men and women of Chinese ethnicity ranging in ages from 45 to 74 at enrollment.
"These are exceptional data on dietary habits," said NIEHS researcher Stephanie London, M.D., lead investigator on the study. "We are fortunate to have access to high quality dietary data from such a large number of participants to address the potential links with respiratory health."
Dr. Mimi Yu, of the University of Minnesota, founder of the Singapore Chinese Cohort, developed and validated a 165-item quantitative food frequency questionnaire in this population. The participants were presented with a list of 147 food items and 18 beverages and asked about the frequency of consumption of each item over a one-year period. For this paper, researchers used these data to analyze dietary patterns of the population, rather than simply looking at individual foods or nutrients as is usually done.
"We were able to identify two distinct food patterns in our population," said Dr. London. "what we refer to as the 'meat-dim sum pattern' and the 'vegetable-fruit-soy pattern.'"
The meat-dim sum pattern contained 31 food items, predominantly pork, chicken, fish, noodle dishes, and preserved foods, as well as 11 snack items. The vegetable-fruit-soy pattern contained 32 foods, including 23 vegetables, 4 fruit items and five soyfood items.
The meat dim sum pattern was positively associated with new onset cough with phlegm after adjusting for age, gender, smoking, education and other factors. No individual food item could account for the 1.4 fold increase in risk of cough with phlegm from this dietary pattern. "It is difficult to tease out what is accounting for the increases in respiratory symptoms related to the meat-dim-sum diet, and thus using the patterns is useful" said Dr. London.
The researchers explain that there are similarities between the newly identified Chinese patterns and U.S. dietary patterns. Two primary U.S. patterns have been consistently described in the research literature. The "Western" pattern, characterized by red and processed meats, sweets and desserts, French fries, refined grains, has many similarities to the Chinese meat-dim sum diet; and the "prudent" pattern, characterized by fruits, vegetables, legumes, fish, poultry and whole grains, resembles the vegetable-fruit-soy diet.
"As researchers, we rarely look at the impact of dietary patterns on health. We typically look at vitamins and specific foods, but not how overall dietary patterns affect non-malignant respiratory diseases or symptoms," said Dr. London. "These data show us the important contribution that diet can have on the development of diseases, such as COPD. Choosing foods with less saturated fat, lower in refined starches and sodium content is probably a good idea."
Researchers at the National University of Singapore, the University of Minnesota, the University of California at Davis, and Fox-Chase Cancer Center collaborated with NIEHS on this study.
Note to Reporters: World COPD Day 2005 will take place on November 16, 2005. World COPD Day is organized by the Global Initiative for Chronic Obstructive Lung Disease (GOLD) in collaboration with health care professionals and COPD patient groups throughout the world. Its aim is to raise awareness about chronic obstructive pulmonary disease (COPD) and improve COPD care throughout the world.
Reference: LM Butler et al. Prospective study of dietary patterns and persistent cough with phlegm among Chinese Singaporeans. American Journal of Respiratory and Critical Care Medicine. Published ahead of print on November 4, 2005 as doi:10.1164/rccm.200506-901OC.
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