Dietary fibre and satiety - Not all fibre is alike

Diets low in energy and fat, such as those typically recommended for obese people are poorly satiating. Adding fibre to low-calorie/low-fat foods may enhance satiety. Consumption of high fibre diets is linked to lower body weight and body fat and less weight gain over time in epidemiological studies. Dietary fibre may impact body weight by many mechanisms including hormonal, intrinsic, and colonic effects. Adding bulk to the diet with fibre will also reduce the energy density of the diet. Satiety signals are generated both pre- and post- absorptively so different types of fibre may be effective by different mechanisms. Viscous fibres have been linked to improved satiety, but insoluble fibres that survive gut transit also are satiating. We conducted an acute, double-blind randomized study to compare the effects of four fibres on satiety. On five separate visits, healthy men and women (n=20) fasting subjects consumed either a low-fibre control muffin (1.6 g fibre) or a high-fibre muffin (8.0 - 9.6 g fibre) for breakfast. Subjects used 100mm visual analogue scales to rate hunger and appetite at baseline and at regular intervals for 180 minutes after muffin consumption. Responses were analyzed as change from baseline. Despite similar amounts of dietary fibre in the four high-fibre muffins, satiety responses varied among treatments. Subjects were significantly less hungry at 180 minutes after consuming either resistant starch or barley with oat fibres than after polydextrose; subjects also felt more satisfied after resistant starch and corn bran than after polydextrose. Additionally subjects were significantly more full after consuming resistant starch, barley with oat fibres, corn bran, and control muffins than after eating the polydextrose muffin. Results from this study support that not all fibres influence satiety equally. Effectiveness of different functional fibres on satiety must be balanced with gastrointestinal tolerance of these fibres. In general, resistant starches are well tolerated while oligosaccharides including fructo- and galacto- may cause gastrointestinal disturbances when consumed in quantities that impact satiety. Other factors to consider when evaluating satiety and fibre are dose of fibre and form of fibre. Generally small doses of any fibre are not effective in altering satiety. Our research with doses of fibre found that mixed fibres in a muffin were only effective at the highest amount of fibre fed, 12 gram dose. A dose response study with fenugreek fibre found that 8 grams of fenugreek fibre was effective in enhancing satiety. Food form studies suggest that whole foods containg fibre are more satiating than beverages, even when isolated fibres are added to the beverages. Thus, public health messages to increase consumption of dietary fibre are widely accepted, although scientific support for isolated fibres impacting body weight are lacking.