May Summary

Trends in Dietary Fiber Intake in the United States, 1999-2008

Dana E. King, MD, MS; Arch G. Mainous III, PhD; Carol A. Lambourne, PhD

The purpose of this study was to determine the level of intake of dietary fiber in a representative adult US population during the past decade, and specifically document progress toward the national goal of increasing intake to USDA/Institute of Medicine recommended levels. Significant public health efforts have focused on increasing fiber intake during the past decade. Much of the available evidence indicates that persons who consume foods high in dietary fiber have a lower prevalence of important risk factors for CVD, including hypertension, obesity, and type 2 diabetes mellitus.      

Data for this study was extracted and differences between groups were determined from the National Health and Nutrition Examination Surveys (NHANES) from the years 1999-2000, 2001-2002, 2003-2004, 2005-2006 and 2007-2008. The surveys are conducted biannually by the National Center for Health Statistics and the Centers for Disease Control and Prevention.  NHANES is a nationally representative, complex, multistage, probability-based survey of the civilian, noninstituationalized population of the United States. The NHANES design for each of the time periods includes an oversampling of minority, low-income, and elderly persons.  Appropriate weighting factors were taken into account when calculating population-based frequency estimates. Variables used in the analyses were drawn from the demographics, examination and questionnaire datasets of NHANES for the five cycles beginning 1999-2000 through 2007-2008 available from the National Center for Health Statistics Web site.  Demographic variables were included to determine the relationship between fiber intake and demographic factors.  Age was transformed into categorical variables with 10-year age intervals.  Other variables used were self-reported health statuses, and body mass index (BMI). 

Participants for the study were adult NHANES participants aged 18 or older who had data collected regarding dietary intake. NHANES database has several advantages, including demographic information, physical examination, and dietary information about the average daily consumption of various foods.

Results showed that there was no trend toward increase fiber intake across the decade and no difference in trends after adjustment for grams per kilocalorie; thus only the unadjusted data are shown (14.8 g/day). Men had higher overall dietary fiber intake than women in all the years examined, but the difference was erased after taking into account different energy intake (measured in kilocalories per day); after adjustment, the fiber intake was 7.0 g/day/1,000 kcal for men vs. 8.1 g/day/1,000 kcal for women. Mexican Americans consistently had the highest average fiber intake, and non-Hispanic blacks the lowest (P<0.0001). Individuals with excellent health status had higher intake than people with poor health status (P<0.0001). Participants with obesity (BMI ≥ 30) consistently reported lower fiber intakes than either normal or overweight individuals across all five cycles after adjustment for energy intake (P<0.0001). With respect to individual food categories that account for the most fiber intake, grains accounted for the largest proportion (43.7%), followed by vegetables (20.8%), fruits (13.0%), dry beans, peas, other legumes, (10.1%), and other (12.4%), based on the most recent NHANES period.  The Goldberg revised method was used to recalculate overall fiber intake for the most recent NHANES cohort to adjust for possible over or underreporting of energy and fiber intake.

The authors concluded that the revised number for average daily dietary fiber intake went down from 15.9 g/day to 14.8 g/day, which is even further from national goals. This study illustrates a lack of meaningful change in average dietary fiber intake during the past decade, which is consistent with other studies that have examined average fiber intake in the United States. These findings are disappointing given that public health messages have been consistently disseminated through a plethora of different media avenues. The national goals have been publicized by several organizations during this past decade only to see a slight decrease in the average intake. It is interesting to note that trends in recent studies of adherence to healthy lifestyle habits have noted declines in fruit and vegetable intake in the United States as well.   

King, D.E., Lambourne, C.A., & Mainous, A.G (2012). Trends in dietary fiber intake in the

United states, 1999-2008. Journal of the Academy of Nutrition and Dietetics, 112(5),

642-648. doi:10.1016/j.jand.2012.01.019.