Background: Dietary fibre-induced satiety offers a physiological approach to body weight regulation, yet there is lack of scientific evidence. This experiment quantified food intake, body weight and body composition responses to three different soluble fermentable dietary fibres in an animal model and explored underlying mechanisms of satiety signalling and hindgut fermentation.
Methods: Young adult male rats were fed ad libitum purified control diet (CONT) containing 5% w/w cellulose (insoluble fibre), or diet containing 10% w/w cellulose (CELL), fructo-oligosaccharide (FOS), oat beta-glucan (GLUC) or apple pectin (PECT) (4 weeks; n = 10/group). Food intake, body weight, and body composition (MRI) were recorded, final blood samples analysed for gut satiety hormones, hindgut contents for fermentation products (including short-chain fatty acids, SCFA) and intestinal tissues for SCFA receptor gene expression.
Results: GLUC, FOS and PECT groups had, respectively, 10% (P < 0.05), 17% (P < 0.001) and 19% (P < 0.001) lower food intake and 37% (P < 0.01), 37% (P < 0.01) and 45% (P < 0.001) lower body weight gain than CONT during the four-week experiment. At the end they had 26% (P < 0.05), 35% (P < 0.01) and 42% (P < 0.001) less total body fat, respectively, while plasma total glucagon-like peptide-1 (GLP-1) was 2.2-, 3.2- and 2.6-fold higher (P < 0.001) and peptide tyrosine tyrosine (PYY) was 2.3-, 3.1- and 3.0-fold higher (P < 0.001). There were no differences in these parameters between CONT and CELL. Compared with CONT and CELL, caecal concentrations of fermentation products increased 1.4- to 2.2-fold in GLUC, FOS and PECT (P < 0.05) and colonic concentrations increased 1.9- to 2.5-fold in GLUC and FOS (P < 0.05), with no consistent changes in SCFA receptor gene expression detected.
Conclusions: This provides animal model evidence that sustained intake of three different soluble dietary fibres decreases food intake, weight gain and adiposity, increases circulating satiety hormones GLP-1 and PYY, and increases hindgut fermentation. The presence of soluble fermentable fibre appears to be more important than its source. The results suggest that dietary fibre-induced satiety is worthy of further investigation towards natural body weight regulation in humans.
Alex’s Notes: I have written about the health benefits of fiber previously, but there are many different forms. I recommend reading my previous write-up for a brief overview of how fibers are different. It’s okay, I’ll wait………..
The current study took a bunch of rats and fed them the exact same normal rat diet with the exception of fiber. Four of the most common fiber types were utilized:
- Cellulose (CELL) found in plants
- Beta-glucan (GLUC) found in cereals (most notably oats and buckwheat)
- Pectin (PECT) found in fruits and vegetables (apples!)
- Fructo-oligosaccharides (FOS) also in fruits and vegetables (inulin; onions)
Each group of rats was given 10% of the wet weight of their food as one of these fibers, and a fifth control group (CONT) was fed 5% cellulose with the difference being extra maize starch. They were fed ad libitum, and after four weeks were killed to measure a bunch of stuff. 10% of the diet seems like a lot, and depending on your eating habits it may very well be. However, this translates to about twice the US recommended daily amount, or roughly 60-70 grams per day.
Looking first at the effects on food intake and body composition, the GLUC, PECT, and FOS groups all ate significantly less (10-19%) than the CONT and CELL groups (which didn’t differ in food intake), had lower bodyweight, lower fat mass, and identical lean mass over the course of the four weeks. It is noteworthy to emphasize here that lean body mass growth was maintained, while fat mass and total bodyweight gain was diminished, which lends support to the notion that soluble fibers play a role in bodyweight and adipose tissue regulation.
For hormonal effects, there were no differences between CONT and CELL, as well as for active GLP-1, CCK, or ghrelin. However, plasma concentrations of PYY and total GLP-1 were greater in the GLUC, PECT, & FOS groups compared to CONT, and GLUC had lower PYY than FOS and PECT, and lower total GLP-1 than FOS. Both GLP-1 and PYY are “satiety hormones” that help regulate food intake and are secreted mainly in the distal small intestine (the portion closer to the large intestine). Given this upregulation was observed in rats fed resistant starch as well, it is interesting to speculate that the satiety effects of dietary fiber only come about with chronic fermentation exposure that provides time and stimulus to change the gut environment. In other words, fiber may only assist satiety if its intake is habitual and if it is fermentable, since the above effects were not observed with cellulose. Also, regarding the lack of change in active GLP-1, it has a half-life of 1-2 minutes so it is expected that it was found unchanged. That is why the researchers also measured total GLP-1, which included both the intact hormone and its primary metabolite, so as to give an “overall” picture of GLP-1 secretion.
The effects on food intake and satiety hormones may in part be from the fiber’s viscosity, which slow the digestion of food and increase gut transit time. However, FOS had similar effects as GLUC and PECT despite not being a viscous fiber. In fact, FOS elicited higher GLP-1 response that GLUC. The thing all three of these fibers did have in common was their ferment ability. Unsurprisingly, total concentrations of fermentation products (i.e. short-chained fatty acids) were significantly greater in GLUC, PECT, & FOS groups than the CELL or CONT.
The overall results of the study at hand are clear-cut. Ignoring the fact that this study was performed with rats, it can be safely suggested that consuming roughly 60-70 grams of fermentable fiber may reduce food intake, bodyweight, and fat mass, preserve lean body mass, and increase satiety. And what is a great source of fermentable fiber? All forms of resistant starch as your best bet, but virtually every vegetable and most fruits are also excellent choices.