Many intervention studies have tested the effect of dietary fibers (DFs) on appetite-related outcomes, with inconsistent results. However, DFs comprise a wide range of compounds with diverse properties, and the specific contribution of these to appetite control is not well characterized. Thus, the influence of specific DF characteristics (i.e. viscosity, gel-forming capacity, fermentability, molecular weight [MW]) on appetite-related outcomes was assessed in healthy humans. We searched MEDLINE and FSTA for controlled human intervention trials, testing the effects of well-characterized DFs on appetite ratings or energy intake. Studies were included only if they reported: 1) DF name and origin, and 2) data on viscosity, gelling properties, fermentability, or MW of the DF materials or DF-containing matrices. In total, 49 papers meeting these criteria were identified, reporting 90 comparisons of various DFs in foods, beverages or supplements in acute or sustained exposure trials. A high proportion of potentially relevant literature was excluded due to lack of adequate DF characterization. In 51 of the 90 comparisons, the DF-containing material of interest was efficacious for at least one appetite-related outcome. Reported differences in material viscosity, MW, or fermentability did not clearly correspond to differences in efficacy, while gel-forming DF sources were consistently efficacious. The overall inconsistent relationships of DF properties with respect to efficacy may reflect variation in measurement methodology, nature of the DF preparation and matrix, and study designs. Methods of DF characterization, incorporation and study design are too inconsistent to allow generalized conclusions about the effects of DF on appetite-related outcomes, and preclude the development of reliable, predictive, structure-function relationships. Improved standards for characterization and reporting of DF sources and DF-containing materials are strongly recommended for future studies on the effects of DF on human physiology.
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