from Heartwire — a professional news service of WebMD.

January 28, 2008 — Results from a new study have confirmed what many have long suspected, that a Western diet, one rich in meat, refined grains, and fried foods, increases the risk of developing the metabolic syndrome [1]. Dairy consumption, on the other hand, appears to offer some protection against this cluster of cardiovascular risk-factor abnormalities.

"There have been a couple of prospective studies looking at different components of diet and the effect on metabolic syndrome, but this study extends things further as we looked at whole dietary patterns," lead investigator Dr Lyn Steffen (University of Minneapolis, MN) told heartwire . "Nobody eats just one food. With the Western diet pattern as a whole, a diet characterized by red and processed meat, fried food, and refined grains, as well low intakes of fruit and vegetables, fish, and whole grains, we were able to observe an increased risk of developing metabolic syndrome."

The results of the study are published online January 22, 2008 in Circulation.

Fried foods also a major culprit

Speaking with heartwire , Steffen said that while dietary intake has been linked to various components of the metabolic syndrome, a cluster of risk factors defined by elevated measurements of waist circumference, blood pressure, fasting glucose levels, triglycerides, and low high-density lipoprotein (HDL) cholesterol, the role of diet in the development of the syndrome as a whole is still undefined.

To look at the relationship between dietary intake and the metabolic syndrome, the investigators obtained data from 9514 participants in the Atherosclerosis Risk in Communities (ARIC) study, excluding individuals with metabolic syndrome or cardiovascular disease at baseline. The group assessed food intake using a 66-item food frequency questionnaire and used this information to categorize dietary preferences as a "Western diet" or "prudent diet." The Western diet was heavy on refined grains, processed meat, fried food, eggs, red meat, and soda, but skimpy on fish, whole grains, and fruits and vegetables. Those categorized as adhering to a prudent diet ate plenty of vegetables, including cabbage, radish, broccoli, carrots, pumpkin, red peppers, and spinach, as well as fruit, fish, seafood, poultry, whole grains, and low-fat dairy products.

After nine years of follow-up, nearly 40% of the ARIC participants studied developed metabolic syndrome. After adjusting for various demographic factors, smoking, physical activity, and energy intake, the consumption of a Westernized diet was associated with an 18% increased risk of developing the metabolic syndrome, whereas Steffen said the prudent dietary pattern had a neutral effect on metabolic-syndrome development.

Further adjusting for the consumption of meat, dairy, fruits and vegetables, refined grains, and whole grains, the analysis showed that meat, fried foods, and diet soda were all individually associated with a risk of developing metabolic syndrome. Dairy consumption, on the other hand, appears to confer protection against developing the disorder.

Nine-year multivariable-adjusted hazard ratios (95% CI) for 3782 cases of metabolic syndrome

Speaking with heartwire , Steffen said the increased risk of the metabolic syndrome associated with the Western diet is likely driven by the risk associated with increased red and processed meat consumption. For example, the consumption of red meat twice daily, those in the highest quintile of consumption, was associated with a 26% increase in risk of the metabolic syndrome compared with those who ate meat just twice per week, or those in the lowest quintile. Another study highlight was the finding that the consumption of fried foods was associated with a 25% increase in risk in developing the metabolic syndrome.

The investigators also showed, much like a study published last year in Circulation and reported by heartwire at that time [2], that diet soda consumption was associated with an increased risk of developing metabolic syndrome, despite the zero calories and zero sugar.

"We're not exactly sure what is going on with diet pop," said Steffen. "It could be that there is some sort of chemical in it that is promoting insulin resistance, or it could be related to behavior, something people are doing to increase their risk. There's no calories in diet pop so maybe people feel less guilty about eating an extra cookie or slice or cake."

Steffen said that the obesity epidemic, and the increasing prevalence of the metabolic syndrome, makes it important to identify whole dietary strategies, and not just specific foods or nutrients, to reduce the risk of developing the multicomponent syndrome. She said individuals would be served well by following the American Heart Association dietary guidelines, which recommend five to nine servings of fruits and vegetables daily, but very few individuals are doing just that. In addition to the fruits and vegetables, two servings of low-fat dairy and three servings of whole grains are recommended each day.

Sources

1. Lutsey PL, Steffen LM, Stevens J. Dietary intake and the development of the metabolic syndrome. Circulation. 2008;DOI:10.1161/circulationaha.107.716159. Available at: https://circ.ahajournals.org.
2. Dhingra R, Sullivan L, Jacques PF, et al. Soft drink consumption and risk of developing cardiometabolic risk factors and the metabolic syndrome in middle-aged adults in the community. Circulation. 2007;116:480-488.

The complete contents of Heartwire , a professional news service of WebMD, can be found at www.theheart.org , a Web site for cardiovascular healthcare professionals.

Clinical Context

Study Highlights

• In the prospective ARIC study, dietary intake was evaluated at baseline in 9514 participants with use of a 66-item food frequency questionnaire.
• Age range of participants was 45 to 64 years.
• "Western" and "prudent" dietary patterns from 32 food groups were determined with principal-components analysis.
• 10 food groups used in previous studies of the ARIC cohort were evaluated.
• Proportional-hazards regression was used to determine associations with the metabolic syndrome, as defined by American Heart Association guidelines (≥ 3 of the following cardiovascular risk factors: waist circumference, blood pressure, fasting glucose, HDL cholesterol, and triglycerides).
• During 9 years of follow-up, 3782 incident cases of metabolic syndrome were identified (in nearly 40% of participants).
• Consumption of a Western dietary pattern was adversely associated with incident metabolic syndrome (P for trend = .03), after adjustment for demographic factors, smoking, physical activity, and energy intake.
• When further adjustment was made for intake of meat, dairy, fruits and vegetables, refined grains, and whole grains, analysis of individual food groups revealed that foods adversely associated with incident metabolic syndrome were meat (P for trend < .001), fried foods (P for trend = .02), and diet soda (P for trend < .001).
• Compared with individuals in the lowest quintile of meat consumption, those in the highest quintile of meat consumption were at 26% greater risk of developing the metabolic syndrome.
• Intake of hamburger, hot dogs, and processed meat seemed to promote the adverse association between meat and incident metabolic syndrome.
• Compared with individuals in the lowest tertile of fried food intake, those in the highest tertile of intake were at 25% greater risk of developing the metabolic syndrome.
• Compared with individuals in the lowest tertile of diet soda intake, those in the highest tertile of intake were at 34% greater risk for the metabolic syndrome.
• After adjustment, dairy consumption was inversely associated with incident metabolic syndrome (P for trend = .006).
• Compared with individuals in the lowest quintile of dairy consumption, those in the highest quintile were at 13% lower risk of developing the metabolic syndrome.
• There were no apparent associations between incident metabolic syndrome and a prudent dietary pattern or intakes of whole grains, refined grains, fruits and vegetables, nuts, coffee, or sweetened beverages.
• Based on these findings, the investigators concluded that consumption of a Western dietary pattern, meat, and fried foods promotes the incidence of metabolic syndrome, whereas dairy consumption is somewhat protective.
• The strength of the direct association between diet soda intake and incident metabolic syndrome was unexpected, meriting further study.
• Limitations of the study include possible reverse causality or residual confounding explaining the association between diet soda and incident metabolic syndrome; use of a food frequency questionnaire containing only 66 items, which could result in an underestimation of energy intake or misclassification of dietary intake; the possibility that dietary intake may be confounded because eating behaviors tend to cluster; and possible reporting bias.

Pearls for Practice

• Consumption of a Western dietary pattern was adversely associated with incident metabolic syndrome, after adjustment for demographic factors, smoking, physical activity, and energy intake.
• After further adjustment for intake of meat, dairy, fruits and vegetables, refined grains, and whole grains, foods adversely associated with incident metabolic syndrome were meat, fried foods, and diet soda. Dairy consumption was inversely associated with incident metabolic syndrome.

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