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Division of Metabolic Diseases
University of Naples SUN
Piazza L Miraglia 2
80138 Naples
Italy
E-mail: dario.giugliano{at}unina2.it
Dear Sir:
We read with interest the study of Sahyoun et al (1) reporting a lower prevalence of the metabolic syndrome and a reduced risk of cardiovascular disease (CVD) mortality in older people consuming diets high in whole-grain foods. Although these results are for the most part confirmatory, adding to the existing evidence that whole-grain intake may confer protection against the metabolic syndrome and CVD risk, the message about the healthy benefits conferred by increasing whole-grain intake in an older population is important. One problem with the study is the use of body mass index (BMI) as a measure of waist circumference. BMI may be not equivalent to waist, either in terms of measurement (cm) or in predicting CV risk. The recent data from the INTERHEART Study (2) clearly showed that, worldwide, waist is superior to BMI in relation to the risk of myocardial infarction. Therefore, the results of Sahyoun et al must be viewed with caution, because their report does not specify how many subjects with abdominal obesity (men with BMI < 31 and women with BMI < 27) escaped evaluation or what was the frequency of abdominal obesity (with BMI used as a surrogate measure) in the definition of the syndrome.
Among the biologically plausible mechanisms of the beneficial effects of whole-grain intake on CVD risk, the authors failed to include inflammation. Recent evidence suggests that inflammation may be an important mediator in the association between the consumption of dietary fiber, one important constituent of whole-grain foods, and CVD. In a nationally representative sample of 4900 adults aged 40–65 y, the likelihood of elevation of C-reactive protein (CRP) was significantly lower in subjects in the highest fiber quartile than in those in the lowest quartile (odds ratio: 0.51; 95% CI: 0.27, 0.95), regardless of age and BMI (3). A cross-sectional analysis of 780 diabetic men from the Health Professionals' Follow-up Study (4) showed that high intakes of cereal fiber were associated with higher plasma concentrations of adiponectin, an insulin-sensitizing adipocytokine with anti-inflammatory properties. Meal modulation of circulating inflammatory and anti-inflammatory cytokines may also play a role in the detrimental or beneficial effects of different types of carbohydrates. For instance, the fiber content of a high-carbohydrate meal may influence plasma concentrations of adiponectin and interleukin 18 (IL-18): the greater the quantity of fiber in the load, the greater the inhibition of plasma IL-18 and the stimulation of adiponectin (5). IL-18 is a potent proinflammatory cytokine that may be important in the process of plaque destabilization and hence in predicting cardiovascular death in patients with acute coronary syndromes (6). It is interesting that, in the study by Sahyoun et al, fasting glucose concentrations decreased across increasing quartile categories of whole-grain intake, a finding consistent with a proinflammatory effect of increasing glucose concentrations (7). Increased consumption of high-density and low-quality foods, such as those rich in refined grains and poor in natural antioxidants and fiber, may cause an activation of the innate immune system, most likely by excessive production of proinflammatory cytokines associated with a reduced production of anti-inflammatory cytokines. This imbalance may favor the generation of an inflammatory milieu, which in turn may predispose susceptible persons to a greater incidence of the metabolic syndrome (8).
ACKNOWLEDGMENTS
Neither of the authors had a personal or financial conflict of interest.
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