Potential misinterpretation of the nutritional value of dietary fiber: correcting fiber digestibility values for nondietary gut-interfering material

Abstract

The aim of this review is to identify the origin and implications of a nondietary material present in digesta and feces that interferes with the determination of dietary fiber in gastrointestinal contents. Negative values for ileal and fecal digestibility of dietary fiber are commonly reported in the literature for monogastric animal species, including humans. As negative values are not possible physiologically, this suggests the existence of a nondietary material in the gastrointestinal contents and feces that interferes with the accurate determination of dietary fiber digestibility when conventional methods of fiber determination are applied. To date, little attention has been given to this nondietary interfering material, which appears to be influenced by the type and concentration of fiber in the diet. Interestingly, estimates of dietary fiber digestibility increase substantially when corrected for the nondietary interfering material, which suggests that currently reported values underestimate the digestibility of dietary fiber and may misrepresent where, in the digestive tract, fermentation of fiber occurs. A new perspective of dietary fiber digestion in the gastrointestinal tract is developing, leading to a better understanding of the contribution of dietary fiber to health.

Ileal and hindgut fermentation in the growing pig fed a human-type diet

“…Results of several experiments also indicate low ileal digestibility values for dietary fibre in human ileostomates and ileal-cannulated pigs (11)(12)(13) . Montoya et al (14) discussed that non-dietary gut materials may interfere with dietary fibre determination in ileal digesta and thus lead to underestimation of dietary fibre ileal digestibility. For instance, an estimate of the ileal digestibility of soluble fibre in kiwifruit increased 50 % units when it was corrected for interfering non-dietary materials (15) .…”

The impact of xylanase and body weight, and their interaction, on the utilization of dietary components in swine

“…The decreased AID of fiber observed in our experiment may be due to increased mucin production, which can contaminate dietary fiber analyses. It has been determined that endogenous materials such as glycoproteins, microbes, and sloughed epithelial cells from the lumen of the gastrointestinal tract may be co-analyzed with dietary fiber when using the NDF, ADF, or TDF methods, resulting in an underestimation of dietary fiber digestion (Montoya et al, 2016). Mucins and bacteria are the primary endogenous materials that are included in and interfere with dietary fiber analyses when measured at the small intestine (Montoya et al, 2016).…”

“…The analytical methods used to measure dietary fiber were developed for the measurement of fiber in food products, but have been used by nutritionists for fiber measurements in ileal digesta and fecal samples in order to calculate fiber digestibility (Montoya et al, 2016). Previous reports of negative fiber digestibility values in monogastric animals, which are not physiologically possible, have called into question the accuracy of these methods when measuring dietary fiber in non-food materials (Wilfart et al, 2007;Cervantes-Pahm et al, 2014b).…”

“…When analyzing dietary fiber, researchers must recognize the limitations of the laboratory assays used and, if possible, make an effort to correct for contamination by non-dietary fiber materials. (Montoya et al, 2016).…”

Relationship between Dietary Fiber Fermentation and Volatile Fatty Acids’ Concentration in Growing Pigs

“…Those results support those reported by Bach Knudsen et al [18], who found that the apparent ileal digestibility (AID) of NSP, which is the difference between TDF and lignin, in pigs, ranged from −7% to 40%. Importantly, some studies have reported that both the gastrointestinal digesta and the feces contain a significant amount of endogenous fibrous components from nondietary materials that interfere with the determination of dietary fiber fermentation [19,20]. The fermentation capacity of dietary fiber that is not corrected for the endogenous loss of fiber components can greatly underestimate dietary fiber fermentation.…”