Implications of two different methods for analyzing total dietary fiber in foods for food composition databases

Since 1989, total dietary fiber values in USDA databases were determined by the enzymatic-gravimetric (EGF) method (AOAC 991.43), where "fiber" is the residue remaining after samples are subjected to enzymatic treatments mimicking digestion. In 2009 EGF was modified to recover additional non-digestible components (e.g., galacto/fructo-oligosaccharides, polydextrose, resistant starch) (AOAC 2009.01, 2011.25) (mEGF). Limited mEGF data and high cost create a need to identify suitable foods for analysis. USDA's National Food and Nutrient Analysis Program sampled suitable foods for analysis by EGF and mEGF. No detectable difference between EGF and mEGF was found in almonds, wheat bread, oatmeal cookies, tortilla chips, taco shells, kale, fast food French fries, or cooked dried pulses. mEGF exceeded EGF in uncooked dried pulses (5.4-10.5 g/100 g), raw potatoes (13.7 g/100 g), and cooked plantains (3.1 g/100 g), and slightly higher (0.7-2.2 g/100 g) in hummus, canned refried beans, prepared wild rice mix, and frozen raspberry berries, concentrate, and puree. Statistical power was hindered by high analytical uncertainty, especially for mEGF (up to 33% RSD), likely due to cumulative errors in the multiple steps comprising mEGF. mEGF analyses should focus on foods containing significant levels of fiber components not included in EGF, and reporting individual, particularly metabolically active, fiber components.