Dietary fibres and appetite : comparing apples and oranges?

Keywords: dietary fibre, satiation, satiety, appetite, energy intake, body weight, viscosity, eating time, gastric emptying, fermentation.

Background and objective:Dietary fibre can contribute in the prevention of overweight and obesity. However, different classes of dietary fibre may have different effects on appetite and energy intake regulation. The aim of this thesis was to investigate the effect of different dietary fibre classes on appetite, and its underlying mechanisms. Both acute and long term effects of dietary fibre classes were explored by diverse study designs, comprising a systematic review, three intervention studies and an observational study.

Methods:First, we systematically reviewed available literature on the relationship between dietary fibre types, satiety, acute and long term energy intake and body weight. Next, in two intervention studies we investigated whether bulking, viscous, and gel forming properties of fibre could be related to satiation (n=121) or satiety (n=29), and whether fibre consumed in different food matrices could be related to satiety (n=29). Then, in a third intervention study (n=32), the role of acute and long term exposure (16 days) to gel forming fibre on satiety and energy intake was explored. Finally, long term (6.4 year) associations between the intake of dietary fibre classes and change in body weight were studied in an elderly population-based prospective cohort (n=1,859).

Results:The literature review of studies in acute settings showed that dietary fibres with viscous properties and dietary fibres consumed in a liquid food matrix increased satiety and lowered subsequent energy intake. In the intervention studies we observed that foods containing a high-dose of gel forming fibre induced earlier satiation and increased satiety. Foods containing bulking and viscous fibres did not affect satiation or satiety. We observed that the earlier satiation and increased satiety were likely mediated by the increased time that was needed to eat the foods. Satiety, but not earlier satiation, was related to a slowed down gastric emptying rate.

The literature review of studies on long term effects indicated that dietary fibre may lower energy intake and body weight, and that not all dietary fibre types are equally effective. Long term changes could, however, not be associated with viscosity, solubility, fermentability or with food matrix properties. In the intervention study we found that a gelled fibre persistently increased satiety compared to control, but did not decrease energy intake or body weight. In the prospective cohort study, a higher intake of total fibre, fibre from different food sources and fibre types were not associated with changes in body weight or waist circumference, although in general inverse associations were observed.

Conclusions:We conclude that fibre classes that are hydrated and thickened result in earlier satiation and increased satiety. These effects are likely mediated by an increased oro-sensory exposure time and a slowed down gastric emptying rate. Dietary fibres may decrease long term energy intake and body weight, yet, we were not able to associate the effects with specific dietary fibre classes or underlying mechanisms.