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Gastric Effects of Dietary Fibre on Fullness

The Stomach's Role in Satiety

The stomach plays a crucial role in generating sensations of fullness and satiety. The physical distension (stretching) of the stomach wall is a key mechanism through which the body signals that sufficient food has been consumed. Dietary fibre, particularly insoluble fibre and high-volume, low-energy-density foods, can influence this gastric distension.

Gastric Distension and Volume

Mechanical Filling

Fibre-rich foods, especially those with high water content and low energy density, occupy significant volume in the stomach. Vegetables, whole grains, and legumes contribute bulk to meals without providing excessive calories. This physical volume stimulates stretch receptors in the stomach wall, generating signals that influence satiety perception.

Sensory Signalling

The stretch of the stomach activates mechanoreceptors (stretch-sensitive nerve endings) in the gastric wall. These receptors transmit signals to the brain via the vagus nerve, contributing to the sensation of fullness during a meal. Larger meal volumes from high-fibre foods generate more pronounced distension and thus more robust signalling.

Energy Density Considerations

A key feature of fibre-rich foods is their typically lower energy density. By providing more volume for fewer calories, high-fibre foods create gastric distension—the mechanical stimulus for fullness—without equivalent caloric intake. This represents a distinct physiological mechanism separate from and complementary to caloric content.

Gastric Emptying and Transit Time

Rate of Stomach Emptying

Gastric emptying—the rate at which the stomach releases its contents into the small intestine—is influenced by multiple factors including meal composition, fibre type, and hydration. Soluble fibre, in particular, increases the viscosity of gastric contents, which can slow gastric emptying rate.

Extended Satiety Signalling

When gastric emptying is slowed, the stomach remains distended for a longer period. This extended duration of gastric distension may prolong satiety signalling during and after meals. The slower movement of food through the upper digestive tract sustains the mechanical stimulus on stretch receptors.

Research Observations

Studies examining gastric emptying in response to soluble fibre have generally observed slower emptying rates compared to low-fibre or refined carbohydrate meals. The magnitude of this effect varies based on the type and amount of soluble fibre consumed.

Subjective Fullness in Short-Term Studies

Eating Rate and Consumption Patterns

Fibre-rich foods often require more mastication (chewing) due to their texture and structure. This increased chewing naturally slows eating rate. Research has shown that slower eating rates can allow more time for satiety signalling to develop, potentially influencing subjective fullness ratings during meals.

Meal Duration

The extended time required to consume fibre-rich foods may allow greater opportunity for cephalic and early satiety signals to influence eating behaviour. These early satiety mechanisms operate before significant caloric intake occurs, potentially modulating further consumption.

Subjective Assessments

Short-term feeding studies commonly measure subjective fullness using visual analogue scales or other subjective rating methods. Many such studies report higher fullness ratings following high-fibre meals compared to low-fibre alternatives of similar caloric content. However, these findings are observational and demonstrate association rather than causal mechanisms.

Complexity and Individual Variation

The relationship between gastric distension, fibre intake, and subjective fullness is complex and varies between individuals. Factors including baseline dietary habits, gastric sensitivity, eating patterns, and psychological associations with food all influence how gastric mechanics translate into subjective sensations of fullness.

Key Takeaway

Dietary fibre, particularly insoluble forms and high-volume, low-density foods, influences gastric distension and gastric emptying rate. These mechanical effects represent distinct physiological mechanisms through which fibre may influence satiety signalling and eating patterns in the short term. Individual responses vary based on multiple physiological and behavioural factors.