Study Reports Whole Grain and Dietary Fiber in American Diets
For your information, Kranz, et al., authored the study “Whole Grains Contribute Only a Small Proportion of Dietary Fiber to the U.S. Diet” published in Nutrients. The study evaluated data from the 2003–2004 to 2009–2010 US National Health and Nutrition Examination Survey (NHANES) to examine the relationship between whole grain (WG) foods and dietary fiber (DF) from these foods. The study was conducted to address the question “what are the food sources of DF consumed by the American population, and what proportion of dietary fiber is contributed by WG?” since public health guidance such as the 2015–2020 Dietary Guidelines for Americans recommend increasing the consumption of WG while studies have shown that WG foods vary in dietary fiber content.
Estimates for total grain, WG, and DF intakes were obtained using one day of dietary intake data collected using a 24-hour dietary recall from 34,391 individuals aged 2 years and older participating in the What We Eat In America (WWEIA) dietary component of the NHANES surveys conducted in 2003–2004, 2005–2006, 2007–2008, and 2009–2010. Researchers estimated WG intake, defined as grains that include the bran, germ, and endosperm, using MyPyramid Equivalents Database (MPED) 2.0 for USDA Survey Food Codes, 2003–2004 (MPED 2.0) and the Center for Nutrition Policy and Promotion Addendum to MPED 2.0. Four categories of dietary fiber density food (no, low, medium, or high dietary fiber) and five categories of WG food (not a grain food, a grain food with no WG, a grain food with low amounts of WG, a grain food with medium amounts of WG, and a grain food with high amounts of WG) were used for data analysis. Kranz, et al., also note that consumption patterns were conducted on the food level rather than individual intake since it is estimated that less than 3 percent of Americans meat the dietary guidance for DF and a small proportion meet the guidance for WG intake.
The researchers report the following findings:
- Survey data reflected the US census with approximately 50% of the subject data collected from males, more individuals were Non-Hispanic white and 29 percent having higher than high school education. It was noted that income disparities were noted with a greater proportion of younger individuals from low-income families while the majority of the adult population was from medium or high-income households.
- Approximately 7% of total fiber intake was from foods containing high amounts of both WG and DF.
- Dietary fiber intake was from both grain and non-grain based foods with grain-based foods contributing 54.5% of all DF consumed and 45.5% of DF coming from non-grain food consumption. Regarding grain based foods, approximately 39% of DF came from grain foods that contained no WG, which contain less DF but are consumed in large quantities. All WG-containing foods combined contributed a total of 15.3% of DF in the American diet.
- Distribution of total DF intake provided by low, medium, and high fiber foods (defined by g fiber/100 g food) did not differ between the total population and the age and gender subgroups.
- Low DF consumers obtained approximately 2/3 of their daily average DF from non-grain food sources while diets high in DF had 25% of DF from medium or high WG foods and 35% from non-grain food sources.
The authors note that the study was designed to highlight the difference between WG, high-fiber WG, and sources of fiber that are not from WG since concerns that efforts to improve DF intake will fail if they are based solely on the recommendation to increase WG foods have been expressed. Importantly the authors note that no generalizable models to predict potential DF from WG foods can be established since only a very small proportion of the American population consumes the recommended amount of WG. The authors conclude “The data presented here show that the WG products consumed by Americans are very low in dietary fiber, thus, public health messaging needs to be changed to encourage consumption of WG foods with high levels of DF to address both recommendations.”