Dietary fibres are believed to reduce subjective appetite, energy intake and body weight. However, different types of dietary fibre may affect these outcomes differently. The aim of this review was to systematically investigate the available literature on the relationship between dietary fibre types, appetite, acute and long-term energy intake, and body weight. Fibres were grouped according to chemical structure and physicochemical properties (viscosity, solubility and fermentability). Effect rates were calculated as the proportion of all fibre-control comparisons that reduced appetite (n = 58 comparisons), acute energy intake (n = 26), long-term energy intake (n = 38) or body weight (n = 66). For appetite, acute energy intake, long-term energy intake and body weight, there were clear differences in effect rates depending on chemical structure. Interestingly, fibres characterized as being more viscous (e.g. pectins, β-glucans and guar gum) reduced appetite more often than those less viscous fibres (59% vs. 14%), which also applied to acute energy intake (69% vs. 30%). Overall, effects on energy intake and body weight were relatively small, and distinct dose-response relationships were not observed. Short- and long-term effects of dietary fibres appear to differ and multiple mechanisms relating to their different physicochemical properties seem to interplay. This warrants further exploration.

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The objective was to determine the effects of dietary fibre with bulking, viscous and gel-forming properties on satiation, and to identify the underlying mechanisms. We conducted a randomised crossover study with 121 men and women. Subjects were healthy, non-restrained eaters, aged 18-50 years and with normal BMI (18·5 -25 kg/m 2 ). Test products were cookies containing either: no added fibre (control), cellulose (bulking, 5 g/100 g), guar gum (viscous, 1·25 g/100 g and 2·5 g/100 g) or alginate (gel forming, 2·5 g/100 g and 5 g/100 g). Physicochemical properties of the test products were confirmed in simulated upper gastrointestinal conditions. In a cinema setting, ad libitum intake of the test products was measured concurrently with oral exposure time per cookie by video recording. In a separate study with ten subjects, 4 h gastric emptying rate of a fixed amount of test products was assessed by 13 C breath tests. Ad libitum energy intake was 22 % lower for the product with 5 g/100 g alginate (3·1 (SD 1·6) MJ) compared to control (4·0 (SD 2·2) MJ, P,0·001). Intake of the other four products did not differ from control. Oral exposure time for the product with 5 g/100 g alginate (2·3 (SD 1·9) min) was 48 % longer than for control (1·6 (SD 0·9) min, P¼0·01). Gastric emptying of the 5 g/100 g alginate product was faster compared to control (P,0·05). We concluded that the addition of 5 g/100 g alginate (i.e. gel-forming fibre) to a low-fibre cookie results in earlier satiation. This effect might be due to an increased oral exposure time.

Results of this exploratory study suggest that despite different sources and composition, fermentable fibers induce a highly similar mucosal response that may at least be partially governed by PPAR-γ.

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