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Fibre-Induced Release of Satiety Hormones

Introduction to Appetite-Regulating Hormones

Appetite and energy intake are regulated by a complex network of hormonal signals acting across multiple tissues, particularly the gastrointestinal tract and brain. Among the most studied appetite-related hormones are glucagon-like peptide-1 (GLP-1) and peptide YY (PYY), both of which are influenced by dietary fibre.

Glucagon-Like Peptide-1 (GLP-1)

Source and Secretion

GLP-1 is a hormone secreted by L-cells, specialised enteroendocrine cells distributed throughout the intestinal epithelium, with the highest concentration in the colon. The release of GLP-1 is stimulated by multiple nutrient-related and non-nutrient stimuli, including fermentation of dietary fibre.

Mechanisms of Fibre-Induced GLP-1 Release

GLP-1 secretion is triggered by several mechanisms related to dietary fibre:

• Direct nutrient sensing: L-cells possess nutrient receptors that respond to glucose and other nutrients, with responses modulated by fibre content of meals
• SCFA signalling: Short-chain fatty acids produced from fibre fermentation activate GPR43 and other receptors on L-cells, directly stimulating GLP-1 secretion
• Mechanical distension: Physical stretching of the intestinal wall from high-volume, fibre-containing meals stimulates mechanoreceptors on L-cells

Physiological Effects of GLP-1

Once secreted, GLP-1 circulates systemically and acts on receptors throughout the body. Within the gastrointestinal system, GLP-1 slows gastric emptying and suppresses gastric acid secretion. In the central nervous system, GLP-1 acts on receptors in the hypothalamus and other appetite-regulating brain regions, influencing hunger and satiety perception. GLP-1 also influences glucose metabolism and has effects on pancreatic beta cells.

Peptide YY (PYY)

Source and Secretion

PYY is also secreted by L-cells and other enteroendocrine cells distributed along the intestine, with particularly high concentrations in the colon. PYY secretion is similarly stimulated by nutrient presence, mechanical distension, and fermentation-derived factors.

Mechanisms of Fibre-Induced PYY Release

Like GLP-1, PYY is stimulated by multiple mechanisms related to dietary fibre intake:

• SCFA activation: Short-chain fatty acids activate receptors (particularly GPR43) on PYY-secreting L-cells
• Nutrient signalling: L-cells respond to the presence of various nutrients, with fibre-containing meals generating specific nutrient sensing patterns
• Mechanical stimuli: Distension of the colonic epithelium by fibrous content stimulates PYY release

Physiological Effects of PYY

PYY circulates systemically and acts on neuropeptide Y (NPY) receptors distributed throughout the gastrointestinal system and brain. In the gut, PYY influences motility and secretion. Notably, PYY enters the circulation in two main forms: PYY(1-36) and the primary degradation product PYY(3-36). PYY(3-36) is particularly associated with appetite suppression and reduced food intake, acting on Y2 receptors in the hypothalamus.

Complementary Roles in Satiety Signalling

GLP-1 and PYY work in overlapping but distinct ways to influence appetite and food intake. Both peptides are released in response to nutrient ingestion and act to promote satiety sensations and reduce hunger. The coordinated release of both hormones in response to dietary fibre represents a synergistic physiological response to fibre-containing meals.

Individual Variation in Hormone Responses

Genotype and Phenotype Differences

Individual responses to dietary fibre, reflected in GLP-1 and PYY secretion patterns, vary based on genetic factors. Genetic polymorphisms in genes encoding fibre-sensing receptors, hormone receptors, and enzymes involved in nutrient metabolism all contribute to inter-individual variation in hormonal responses to fibre intake.

Microbiota-Dependent Responses

The production of SCFAs from fibre fermentation depends on microbiota composition. Since SCFAs are a primary driver of GLP-1 and PYY secretion from fibre, individuals with microbiota compositions more efficient at fermenting dietary fibre will generate greater SCFA concentrations and potentially greater GLP-1 and PYY responses.

Baseline Metabolic State

Baseline metabolic state, including insulin sensitivity, glucose tolerance, and body composition, influences hormonal responses to nutrients. The same fibre intake may generate different GLP-1 and PYY responses depending on individual metabolic characteristics.

Research Context

Research examining GLP-1 and PYY responses to dietary fibre has generally observed increased secretion of both hormones following fibre-containing meals compared to low-fibre alternatives. However, the magnitude of responses varies considerably between studies and between individuals within studies, reflecting the complexity of these hormonal systems.

Key Takeaway

Dietary fibre influences the secretion of GLP-1 and PYY, hormones involved in appetite regulation and energy homeostasis, through multiple mechanisms including SCFA signalling, direct nutrient sensing, and mechanical stimulation. Individual responses to fibre-induced hormone secretion vary based on genetics, microbiota composition, and metabolic state. These hormonal mechanisms represent important physiological pathways through which fibre influences appetite and energy intake.