Page 15 - Nutrinsight-1

About the value of controlling appetite • NutrInsight
The effects of fibre on satiation and satiety
Today numerous data arising from clinical and animal studies indicate that dietary fibre plays a role in satiation and/or satiety, and suggest that an increase in the intake of fibre could help to regulate bodyweight (67;68;69). Indeed, fibre modifies several of the properties of foods that stimulate satiety such as palatability, texture and energy density (they provide less energy, with a calorie content of between 0 and 2 kcal/g). Foods that contain high levels of fibre also require more energetic and more prolonged chewing, which could reduce the rate of ingestion and increase the gastric volume, thus promoting rapid satiation. However, the property of fibre that has the greatest impact on
satiation is its viscosity.
Thus, soluble fibre (one of the two groups of fibre, the other being that of the
in- soluble fibre) has the ability to absorb water and swell up. During a meal, such fibre could increase the volume of the alimentary bolus and stimulate the receptors sensitive to gastric distension. It also slows the gastric emptying and/or intestinal absorption of nutrients and modulates the secretion of specific hormones throughout the length of the digestive tract; all of these factors promote rapid satiation and stimulate satiety (70;71;72).
However, all types of soluble, viscous fibre do not have the same viscosity properties. Their viscosity potential (ability to form a gel with more or less viscosity with the same quantity of water) and the ability of the gel to resist ingestion and digestion (change in pH and temperature, exposure to enzymes) differ from one form of fibre to another. Guar gum has been investigated in particular, and has been found to be more stable (resistant) during digestion than other common forms of dietary fibre. This is the fibre that has undergone most investigation for its effects on satiety. The very high levels of viscosity of solutions containing guar gum have for example been used in a study simulating digestion in the stomach and small intestine in Man; the findings suggest that guar gum could potentially slow digestion and affect certain physiological responses, such as post-prandial blood sugar levels, lipaemia, prolonging the sensation of satiety (71).
Overall, most of the thirteen studies of guar gum carried out in adults gave positive results with regard to subjective parameters of satiety (73;74).
The value of slowly-digestible carbohydrates
All digestible carbohydrates have the same, moderate calorie content (4 kcal/g), but their metabolic fate can influence satiety during the post-prandial period. The main mechanism of action of digestible carbohydrates on satiety results from the regulation of blood sugar. The consumption of slowly digestible carbohydrates induces a more moderate blood sugar peak during the first phase of the post-prandial period, but above all it permits the sustained appearance of carbohydrates at the end of the post-prandial period (75;76). This uptake of glucose several hours after the meal could provide a better response to the glucose needs of certain tissues, such as the brain (see «glucostatic theory», paragraph 1.2) (9).
At the same time, a more moderate glycaemic peak at the beginning of the post-prandial period induces a secretion of insulin that is also more moderate, which should result in greater utilisation of lipids; the glycogen stored is spared and can be used to maintain the blood sugar at its baseline level throughout the next post-absorptive episode, and until the next meal. These two mechanisms therefore seem to act in a complementary fashion to provide better regulation of blood sugar levels at the end of the post-prandial period and therefore limit the sensations of hunger.
Most foods containing high levels of slowly digestible carbohydrates are starchy foods with a low glycaemic index (GI). Foods with a low GI do not all contain slowly digestible carbohydrates (for example, sodas containing fructose), and not all starchy foods have a low GI (for example extruded cereals) (77;78). Several studies have shown that when obese or overweight subjects are subjected to calorie restriction, a low GI diet facilitates weight loss by factors including better satiety. In subjects with normal bodyweight on a balanced diet, it seems to be easy for them to maintain their bodyweight with this type of low-GI diet (79;80;81).
15