点击显示 收起
Department of Human Nutrition
School of Nutrition and Food Technology
Shaheed Behshti University of Medical Sciences
PO Box 19816-19573
Tehran
Iran
E-mail: esmaillzadeh{at}yahoo.ca
Dear Sir:
In an interesting study of older adults in a recent issue of the Journal, Sahyoun et al (1) reported the association between whole- and refined-grain intakes, the metabolic syndrome, and cardiovascular disease (CVD) mortality. After control for some potential confounding variables, the authors concluded that whole-grain intake is inversely associated with the metabolic syndrome and CVD mortality in this age group.
Metabolic syndrome and CVD mortality in elderly people are certainly worthwhile topics for study, particularly when the intake of whole grains is considered. Although whole grains contain higher amounts of health-protective nutrients than do refined grains (2), little research has been conducted on the physiologic effects of a diet high in whole grains, particularly in older adults. However, we think that there are some difficulties with the study of Sahyoun et al that may confound the results. The authors enrolled their subjects on the basis of their willingness to participate in the study, but they did not select the subjects randomly from a population of older persons. We cannot, therefore, extrapolate the results to other older adults. It is not clear how the authors treated underreporters and overreporters of energy intake with respect to study participation. This point is important because the studied population is elderly; previous studies have shown that underreporting of energy intake increases directly with age (3). Although Sahyoun et al controlled for the effect of energy intake in their analysis, it should be kept in mind that some foods are underreported more than other foods (4), and simply implementing a control for energy intake does not correct for the confounding that may be caused by underreporting. Another important issue has to do with which foods are categorized as whole grains and which ones as refined grains. Furthermore, the authors did not mention whether there was any significant interaction between sex and whole-grain intake. We showed that the association of whole-grain intake and the metabolic syndrome in healthy Tehranian adults is similar in the 2 sexes (5), but it remains to be shown whether similar associations exist between whole-grain intake and the metabolic syndrome in elderly men and women.
The independent association of whole- and refined-grain intakes with chronic diseases should be assessed by control for the effect of other food. For example, recent evidence from 2 parts of a study showed the beneficial effects of dairy products, fruit, and vegetables on body weight (6) and the metabolic syndrome (7). Lack of control for the effects of other foods in the study of Sahyoun et al makes the conclusion misleading. Another major weakness of their study of Sahyoun et al is that they used a 3-d dietary record to collect dietary data. This method of gathering data does not reflect the subjects' usual dietary intake; because a 3-d dietary record measures short-term intake, its use as a predictor of a long follow-up analysis is problematic (8).
It seems that the proportion of women in the highest quartile of whole-grain intake is less than that in the lower quartiles. This finding that more men than women are seating whole grain is unusual, and it may be confounded with energy intake, because men probably eat more food in general than do women. However, energy intake increases with the quartiles of both refined-grain and whole-grain intake. Do the sex-specific data shed any light on this issue? The finding that energy intake increases significantly across quartiles of whole-grain intake, whereas BMI decreases, is also somewhat questionable. Identifying diet-disease relations is extremely important in preventing chronic diseases. However, careful methods should be adopted to avoid incorrect conclusions.
ACKNOWLEDGMENTS
Neither of the authors had a conflict of interest.
REFERENCES