A large study surveyed 24-hour dietary fiber intake in a nationally representative sample of the United States population. The investigators also collected anthropometric and laboratory data soon after survey completion. The following results were reported for prevalence of obesity, metabolic syndrome, and elevated inflammatory markers per quintiles of daily dietary fiber intake. Which of the following is the best interpretation of the study results?
A)Higher dietary fiber intake consistently causes a decrease in inflammatory biomarkers
B)Higher dietary fiber intake is beneficial in obese patients with high inflammatory biomarkers
C)Lower dietary fiber intake results in obesity and metabolic syndrome
D)The relative risk of cardiac disease is lower with higher dietary fiber intake
E)There is an association between higher dietary fiber and a lower prevalence of metabolic syndrome

Question

A large study surveyed 24-hour dietary fiber intake in a nationally representative sample of the United States population.  The investigators also collected anthropometric and laboratory data soon after survey completion.  The following results were reported for prevalence of obesity, metabolic syndrome, and elevated inflammatory markers per quintiles of daily dietary fiber intake.  Which of the following is the best interpretation of the study results?
A)Higher dietary fiber intake consistently causes a decrease in inflammatory biomarkers 
B)Higher dietary fiber intake is beneficial in obese patients with high inflammatory biomarkers 
C)Lower dietary fiber intake results in obesity and metabolic syndrome 
D)The relative risk of cardiac disease is lower with higher dietary fiber intake 
E)There is an association between higher dietary fiber and a lower prevalence of metabolic syndrome

Quizplus · Accepted Answer

Explanation: The slope for the metabolic syndrome curve is negative (downward curve), so there is an association between higher dietary fiber intake and decreased prevalence of metabolic syndrome. The corresponding P value is <0.05, so the association is statistically significant. A similar analysis can be conducted for the inflammatory markers and obesity curves. (Choices A and C) The prevalence of inflammatory markers decreases with increasing quintiles of dietary fiber intake, but this association does not mean that higher fiber intake causes this decrease. Similarly, lower fiber intake is associated with a higher prevalence of obesity and metabolic syndrome, but this does not imply causation. (Choice B) A P value for the combined group is necessary to comment on patients with obesity and high inflammatory markers. This study does not provide such information. (Choice D) The relative risk expresses the outcome in one group compared to another. The variables studied are potential risk factors for cardiac disease. However, no information is given regarding the relative risk of cardiac disease. Educational objective: Association does not imply causation.

A Large Study Surveyed 24-Hour Dietary Fiber Intake in a Nationally