Better biomarkers and trials needed to show fiber benefits:Review

The study, published in Nutrition Reviews​, suggests that although many synthetic fibers have begun to show promise in delivering health benefits, there is no evidence from long-term studies to suggest that man-made fiber ingredients and supplements work in reducing disease risk – especially if they are substituting whole grain or vegetables which are a naturally rich source of fiber, and contain other nutrients and vitamins.

“Progress is foreseen in this area, but in order for it to occur, the performance of a series of mechanistic intervention studies of both natural and man-made fibers is required,”​ said the researchers, led by Kaisa Raninen from the Department of Clinical Nutrition, at the University of Eastern Finland.

Dietary fiber​

High consumption of dietary fiber has been linked with a reduced risk of diabetes, gastrointestinal disorders, hypertension, cardiovascular disease, and obesity.

“The physiological mechanisms underlying the health-protective properties of dietary fiber have been studied intensively, and a range of functions throughout the gastrointestinal tract have been elucidated,”​ said the researchers.

Epidemiological evidence of the health-protective effects of dietary fiber have been considered convincing enough for the consumption of dietary fiber to be promoted in dietary recommendations, and has led to industrial interest in developing fiber ingredients to increase the fiber content of processed foods.

Raninen and co-workers said that the objective of the review was to compare the physiological effects of three types of dietary fiber with varying compositions, degrees of chemical and structural heterogeneity, origins, and physical properties.

Health benefits​

The reviewers explained that grain fiber, inulin, and polydextrose are examples of very different types of fibers, which are highly variable in both their technical and physiological functionality.

“By comparing the literature on the physiological responses of grain fiber (representing the plant cell wall-associated fiber), inulin (isolated soluble fiber of plant origin), and polydextrose (synthetic soluble fiber), this review attempts to elucidate the “minimum physiological requirements” for food material ​to be classified as dietary fiber,”​ they said.

The reviewers said that published evidence “shows clearly that inulin and polydextrose can exert some beneficial gastrointestinal effects that are similar to those of grain fibers and thus fulfill both of the definitions of dietary fiber in this respect.”​

However they reported that the evidence supporting beneficial effects on postprandial blood glucose and fasting cholesterol levels have been modest for synthetic fibers – whilst natural grain fibers have shown “variable effects.”​

Raninen and colleagues said it is likely that many more health-promoting mechanisms for dietary fiber will emerge in the future – including beneficial effects on immunomodulation and anti-inflammatory properties.

“Accumulating information might help establish a more detailed set of criteria for dietary fiber with regard to its role in different diseases,”​ they said.

“New biomarkers are needed to link the physiological functions of specific fibers with long-term health benefits, such as modifications of glucose and lipid metabolism,”​ they added.

Source: Nutrition Reviews​
Volume 69, Issue 1, pages 9–21, doi: 10.1111/j.1753-4887.2010.00358.x
“Dietary fiber type reflects physiological functionality: comparison of grain fiber, inulin, and polydextrose”​
Authors: K. Raninen, J. Lappi, H. Mykkänen, K. Poutanen